UDK 621.3:(53+54+621+66)(05)(497.1)=00 ISSN 0352-9045 Strokovno društvo za mikroelektroniko elektronske sestavne dele in materiale MIDEM 2011 Strokovna revija za mikroelektroniko, elektronske sestavne dele in materiale Journal of Microelectronics, Electronic Components and Materials INFORMACIJE MIDEM, LETNIK 41, ST. 2(138), LJUBLJANA, junij 2011 UDK 621.3:(53+54+621+66)(05)(497.1)=00 ISSN 0352-9045 INFORMACIJE MIDEM 2 o 2011 INFORMACIJE MIDEM LETNIK 41, ŠT. 2(138), LJUBLJANA, JUNIJ 2011 INFORMACIJE MIDEM VOLUME 41, NO. 2(138), LJUBLJANA, JUNE 2011 Revija izhaja trimesečno (marec, junij, september, december). Izdaja strokovno društvo za mikroelektroniko, elektronske sestavne dele in materiale - MIDEM. Published quarterly (march, june, september, december) by Society for Microelectronics, Electronic Components and Materials - MIDEM. Glavni in odgovorni urednik Editor in Chief Dr. Iztok Šorli, univ. dipl.inž.fiz., MIKROIKS, d.o.o., Ljubljana Tehnični urednik Executive Editor Urednik elektronske izdaje Editor of Electronic Edition Dr. Iztok Šorli, univ. dipl.inž.fiz., MIKROIKS, d.o.o., Ljubljana Dr. Kristijan Brecl, univ.dipl.inž.el., Fakulteta za elektrotehniko, Ljubljana Uredniški odbor Editorial Board Časopisni svet International Advisory Board Dr. Barbara Malič, univ. dipl.inž. kem., Institut "Jožef Stefan", Ljubljana Prof. dr. Slavko Amon, univ. dipl.inž. el., Fakulteta za elektrotehniko, Ljubljana Prof. dr. Marko Topič, univ. dipl.inž. el., Fakulteta za elektrotehniko, Ljubljana Prof. dr. Rudi Babič, univ. dipl.inž. el., Fakulteta za elektrotehniko, računalništvo in informatiko Maribor Dr. Marko Hrovat, univ. dipl.inž. kem., Institut "Jožef Stefan", Ljubljana Dr. Wolfgang Pribyl, Austria Mikro Systeme Intl. AG, Unterpremstaetten Prof. dr. Janez Trontelj, univ. dipl.inž. el., Fakulteta za elektrotehniko, Ljubljana, PREDSEDNIK - PRESIDENT Prof. dr. Cor Claeys, IMEC, Leuven Dr. Jean-Marie Haussonne, EIC-LUSAC, Octeville Darko Belavič, univ. dipl.inž. el., Institut "Jožef Stefan", Ljubljana Prof. dr. Zvonko Fazarinc, univ. dipl.inž., CIS, Stanford University, Stanford Prof. dr. Giorgio Pignatel, University of Padova Prof. dr. Stane Pejovnik, univ. dipl.inž., Fakulteta za kemijo in kemijsko tehnologijo, Ljubljana Dr. Giovanni Soncini, University of Trento, Trento + Prof. dr. Anton Zalar, univ. dipl.inž.met., Institut Jožef Stefan, Ljubljana Dr. Peter Weissglas, Swedish Institute of Microelectronics, Stockholm Prof. dr. Leszek J. 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Grafična priprava in tisk BIRO M, Ljubljana Printed by Naklada 1000 izvodov Circulation 1000 issues Poštnina plačana pri pošti 1102 Ljubljana Slovenia Taxe Percue UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana ZNANSTVENO STROKOVNI PRISPEVKI PROFESSIONAL SCIENTIFIC PAPERS M.Koričic, T.Suligoj: Inženiring parametra BVCEO v SOI LBT tranzistorski strukturi z baznim kontaktom na vrhu 77 M.Koričic, T.Suligoj: BVceo Engineering in SOI LBT Structure with Top Contacted Base M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko, D.Miljavec: Strukturiranje mehkomagnetnega kompozitnega materiala 86 M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko, D.Miljavec: Structuring Soft-magnetic Composite Materials B.Mušič, A.Žnidaršič, P.Venturini: Absorberji elektromagnetnega valovanja 92 B.Mušič, A.Žnidaršič, P.Venturini: Electromagnetic Absorbing Materials M.R.I.Faruque, M.T.Islam, N.Misran: Vpliv dodatka metamateriala na absorpcijo EM valovanja v človeški glavi 97 M.R.I.Faruque, M.T.Islam, N.Misran: Analysis of Metamaterial Attachment for EM Absorption in Human Head A.T.Mobashsher, M.T.Islam, N.Misran: Načrtovanje in razvoj kompaktnih mikrostrip anten za uporabo v prenosnih napravah 105 A.T.Mobashsher, M.T.Islam, N.Misran: Design and Development of Compact Microstrip Antennas for Portable Device Applications A.Rezaul, M.T.Islam, N.Misran: Dvojno polarizirana mikrostrip antena za Ku-frekvenčni pas 114 A.Rezaul, M.T.Islam, N.Misran: Dual Polarized Microstrip Patch Antenna for Ku-Band Application M.R.Alam, M.B.I.Reaz, M.A.M.Ali, S.A.Samad: Modeliranje človeškega obnašanja v pametnih hišah 118 M.R.Alam, M.B.I.Reaz, M.A.M.Ali, S.A.Samad: Temporal Modeling of Human Activity in Smart Homes N.Semenič, A.Sarjaš, R.Svečko, A.Chowdhury: Načrtovanje in implementacija RCP sistema v okolju Matlab/Simulink 122 N.Semenič, A.Sarjaš, R.Svečko, A.Chowdhury: Design and Implementation of Rapid Control Prototyping System with Matlab/Simulink K.Benkič, M.Malajner, Ž.Čučej: AeWSN: akademsko izobraževalno brezžično senzorsko omrežje 132 K.Benkič, M.Malajner, Ž.Čučej: AeWSN: Academic Educational Wireless Sensor Network A.Švigelj, J.Trontelj: THZ vizijski sistem za odkrivanje skritih predmetov 139 A.Švigelj, J.Trontelj: THZ Imaging System for Hidden Objects Detections B.Batagelj, L.Pavlovič, L.Naglič and S.Tomažič: Zlivanje mobilnih in fiksnih omrežij s tehnologijo prenosa radijskega signala preko optičnega vlakna 144 B.Batagelj, L.Pavlovič, L.Naglič and S.Tomažič: Convergence of Fixed and Mobile Networks by Radio over Fibre Technology Andrej Ikica, Peter Peer: Anotirana podatkovna baza slik teksta v naravnih scenah CVL OCR DB in njena uporaba 150 Andrej Ikica, Peter Peer: CVL OCR DB, an Annotated Image Database of Text in Natural Scenes, and Its Usability Zapisnik občnega zbora strokovnega društva MIDEM z dne 24. 3. 2011 155 MIDEM Assembly minutes, 24.3.2011 MIDEM prijavnica 158 MIDEM Registration Form Slika na naslovnici: Kolaž fotografij vzetih iz prispevkov v tej številki Front page: Collage of pictures taken from contributions published in this issue VSEBINA CONTENT Obnovitev članstva v strokovnem društvu MIDEM in iz tega izhajajoče ugodnosti in obveznosti Spoštovani, V svojem več desetletij dolgem obstoju in delovanju smo si prizadevali narediti društvo privlačno in koristno vsem članom.Z delovanjem društva ste se srečali tudi vi in se odločili, da se v društvo včlanite. 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Prijavnice pošljite na naslov: MIDEM pri MIKROIKS Stegne 11 1521 Ljubljana Ljubljana, junij 2011 Izvršilni odbor društva UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)1, Ljubljana BVceo ENGINEERING IN SOI LBT STRUCTURE WITH TOP CONTACTED BASE Marko Koričic, Tomislav Suligoj Department of Electronics, Microelectronics, Computing and Intelligent Systems, Faculty of Electrical Engineering and Computing, University of Zagreb, Zagreb, Croatia Key words: SOI, lateral bipolar transistor, extrinsic base, charge sharing effect, common-emitter breakdown voltage, cutoff frequency Abstract: Properties of SOI LBT structure with the base contact on top are analyzed by device simulations. The effect of the extrinsic base width on the common-emitter breakdown voltage (BVCEO) is studied in detail. Charge sharing between extrinsic and intrinsic base acceptors can be controlled to achieve fully depleted collector. Shielding of the electric field across intrinsic junction by the extrinsic base electric field can be used to limit the peak value of the electric field along the current path in the collector-base depletion region and to increase the value of BVCEO. Two peaks of electric field appear in the base-collector depletion region - the first one at the intrinsic junction and the second in the drift region toward extrinsic collector. The area in which breakdown occurs depends on the value of the electric field in two peaks, which can be controlled by the extrinsic base width (wbext). Inženiring parametra BVCEO v SOI LBT tranzistorski strukturi z baznim kontaktom na vrhu Kjučne besede: SOI, bipolarni tranzistor, ekstrinzična baza, deljenje naboja, prebojna napetost s skupnim emiterjem, mejna frekvenca Izvleček: Simulirali smo lastnosti SOI LBT tranzistorske strukture z baznim kontaktom na vrhu. Podrobno smo proučili vpliv širine ekstrinzične baze na prebojno napetost tranzistorja, BVCEO Kontroliramo lahko porazdelitev naboja akceptorjev intrinzične in ekstrinzične baze, da dosežemo popolnoma osiromašen kolektor. Senčenje električnega polja ekstrinzične baze čez intrinzičen spoj lahko uporabimo za omejitev najvišje vrednosti električnega polja vzdolž tokovne poti v osiromašenem področju spoja kolektor-baza, kakor tudi za povečanje prebojne napetosti BVCEO Pojavita se dva vrhova električnega polja v osiromašenem področju spoja baza-kolektor. Področje, kjer pride do preboja, je odvisno od vrednosti električnega polja teh dveh vrhov, ki ju lahko kontroliramo s širino baze, wbext. 1. Introduction Recently, the extremely-thin silicon-on-insulator (SOI) has been marked as a potential CMOS technology for 22 nm node and below, /1/. Small parasitic capacitances inherent for SOI technology, good electrostatic behavior and low variability due to undoped channel promise a good solution for short channel effects (SCE) and scaling properties of such CMOS. This trend in IC industry will force SOI wafer manufacturers to improve wafer production in terms of lower defect density and reduced cost. It can be expected that wafer cost of not only ultra-thin-film SOI, but also thicker film SOI, will be reduced in the near future. In the past years, thin-film SOI technology has been proposed as a potential technology for radio-frequency (RF) system-on-chip (SoC) integration /2/, /3/. Excellent characteristics regarding the device isolation and small parasitic capacitances, as well as higher quality passives compared to bulk-silicon technologies, make this technology appropriate for low-power battery supplied applications like mobile phones, GPS, WiFi, etc. In order to achieve SoC level of integration for RF applications, bipolar transistors are desired in a technology platform due to their superior analog performance such as lower noise figure and higher gain. Vertical bipolar transistors in SOI may become prohibitively expensive due to more complex process /4/, which in addition to the higher cost of SOI wafers may result in a technology that is not economically viable. On the other hand, lateral bipolar transistors (LBTs) in SOI can be fabricated in a process that is less complex with the significant cost reduction compared to the vertical bipolar transistors, either in bulk or SOI substrates. It can be expected that cost of technology will be reduced further with the advance in SOI wafer manufacturing. Due to the nature of intrinsic base fabrication, which relies on the spacer technique and lateral redistribution of impurities, cutoff frequencies (fT) of SOI LBTs above 20 GHz were not reported. The only LBT with reported state-of-the-art electrical performance is Horizontal Current Bipolar Transistor (HCBT) but it is fabricated in bulk-silicon wafers /5/. However, reported AC performance of SOI LBTs is still suitable for applications in microwave frequency range including the most important wireless application standards. Several LBT structures have been proposed so far and can be roughly categorized with respect to the base contact position as laterally contacted /6/, /7/, /8/ and top-contacted structures /2/, /3/, /9/, /10/. One benefit of placing the base contact on the top is that transistor length can be increased in the third dimension by the mask design if higher current drive is needed in the applications. In the case of laterally contacted base, i.e. two-sided base contact, transistor 665 Informacije MIDEM 41(2011)2, str. 77-85 M. Koricic, Tomislav S.: BVceo Engineering in SOI LBT Structure with Top Contacted Base operating current cannot be increased by increasing the emitter length, because the intrinsic base resistance would be increased. The ultimate result is that AC performance of the transistor is degraded through the reduction of maximum oscillation frequency (fmax). To overcome this issue, transistors of unit emitter size can be connected in parallel, which gives less flexibility in the circuit design. In order to achieve a SoC level of integration, transistors with different values of breakdown voltages should be available in a certain technology. In standard vertical transistors it is accomplished by the different parameters of the selectively implanted collector, which implies the usage of additional lithographic masks and results in an increased process complexity and ultimately higher cost of technology. On the other hand, in LBT structures with top contacted base, different values of breakdown voltages can be obtained by the mask design and the control of the width of the base contact region, i.e. extrinsic base width (wbext), without any increase in the process complexity. In this paper, design tradeoff between cutoff frequency (fT) and common-emitter breakdown voltage (BVCEO), specific for SOI LBT structure with top-contacted base are analyzed by the device simulations. Physical mechanisms in the extrinsic base effect on transistor's breakdown voltage are analyzed in detail. 2. Simulation structure A typical LBT structure such as the one reported in /2/ is analyzed by device simulation in MEDICI. The highest maximum oscillation frequency (fmax) and common emitter current gain (b) as well as the lowest base resistance (RB) among all LBTs are reported for this structure. Cross-section of the device with marked geometrical parameters and the doping profile of the intrinsic transistor are shown in Fig. 1 and 2, respectively. Technological parameters are summarized in Table 1. Emitter height (hE) is determined by the thickness of the silicon on insulator film and the small link-base region (lb), which is defined during the extrinsic Table 1. Technological and geometrical parameters of the soi lbt simulation structure E u e o 4a S S o c o u 0.0 0.1 0.2 Distance, (im Fig. 2. Doping profile of the intrinsic transistor. base polysilicon overetching. In this way, the extrinsic base profile, which is diffused from the extrinsic-base polysilicon, does not overlap the upper edge of the emitter, which could reduce the current gain and degrade base current ideality at lower base-emitter voltages due to the high-field effects and band to band tunneling /11/. Intrinsic transistor is formed by ion implantation of the intrinsic base and emitter, which are separated by the spacer formed on the sidewall defined during the extrinsic base polysilicon etching. Later on in the process, dopants are laterally diffused to form the final intrinsic transistor profile. This represents the fundamental limit on the control of the intrinsic base profile and basewidths cannot be scaled below 100 nm as it is routinely done in standard vertical bipolar transistors. Since the emitter region is not implemented in polysilicon, the distance between emitter contact and the base-emitter junction should be larger than the minority hole diffusion length in order to obtain smaller associated component of the base current and the larger current gain. The minimum distance between highly doped n+ collector contact region, i.e. extrinsic collector, and the p+ extrinsic base is limited by breakdown voltages of the transistor. Extrinsic base polysilicon should be highly doped and thick enough to suppress electron diffusion to the extrinsic base region, which could NABext, (cm-3) NdC, (cm-3) Nde, (cm-3) (nm) l k (nm) dpoly, (nm) dE (nm) dc (nm) dOX (nm) 1 • 1 (nm) 10"3 ■ --Simulated lg -Simulated 2-1020 1.51017 1.8-1020 500 70 120 200 300 500 300 10" O Measured 10"5 - A Measured /c dE dc i - B E dpoly p" ext. base poly c ib : hE[ \ n , n dox BOX ' \ / p intr base collector contact region S fc a o Fig. 1. Cross-section of the device simulation structure with marked geometrical parameters. Fig. 0.2 0.4 0.6 0.8 1.0 Base-Emitter Voltage , V 3. Simulated Gummel characteristics. Measured data from /2/ is included for reference. 78 KM. KoriciC, Tomislav S.: BVceo Engineering in SOI LBT Structure with Top Contacted Base Informacije MIDEM 41(2011)2, str. 77-85 increase the base current and degrade the current gain (b). This structure has the base contact placed on the top and the base current is supplied only from one direction. Therefore, one-sided base contact is formed, which is not beneficial regarding the value of the base resistance (RB). Nevertheless, the smallest RB and the highest fmax value among SOI LBTs are reported for this structure, owing to a small thickness of SOI film and silicided base contact, which results in a small intrinsic component of the base resistance and a small contact resistance, respectively. 3. Simulation of electrical characteristics Simulated Gummel characteristics of the transistor are presented in Fig. 3. Measured data is taken from /2/ for the reference. Doping profile in the intrinsic base is adjusted to get reasonable fit of the collector current. Summary of the simulated characteristics is given in Table 2. Table 2. Summary of the simulated electrical characteristics p f (GHz) fmax, (GHz) rb, (") cbc, (fF) 83 12.7 67.1 250 1.55 3.1. Analysis of common emitter breakdown voltage and cutoff frequency Tradeoff between speed and the breakdown voltage in bipolar transistors is well known. In order to suppress base widening at higher collector currents (i.e. Kirk effect) and to increase the cutoff frequency of the transistor (fT), collector doping concentrations are increased, which results in a higher electric field in the base collector depletion region and lower value of breakdown voltages. Common emitter breakdown voltage (BVCEO) is more important since it is typically 2 to 3 times lower than the common base breakdown voltage (BVcbo) and is responsible for evaluation of transistor's safe operating area. The tradeoff is usually evaluated in terms of (fTBVCEO) product, bounded by the Johnson's limit /12/, which approximately equals 200 GHzV and 400 GHzV for implanted base and SiGe epi-base transistors, respectively /13/. Cutoff frequency (fT) and common emitter breakdown voltage (BVCEO) are simulated in MEDICI. fT is calculated from AC analysis. Y-parameters are simulated and converted to ^-parameters. fT is determined as the frequency at which, h21 falls to unity. For evaluation of the common emitter breakdown voltage, base current reversal method in forced VBE measurement is used /13/. Base-emitter voltage (VBE) is set to 0.7 V and collector-emitter voltage (VCE) is swept. BVCEO is determined as the VCE at which the base current changes the sign, i.e. turns from positive to negative. Non-local impact ionization model based on lucky electron model with hard threshold energy /14/ is used in simulations. All BVCEO simulations are done with standard drift-diffusion model and the effects of self-heating are not considered. However, simulations are done for VBE of 0.7 V at which collector current is small and no substantial self-heating is expected. The unique geometry of LBTs with the base contact placed on the top results in a collector region which is surrounded by the extrinsic base from the top, the intrinsic base from one side and buried oxide from the bottom (Fig. 1). In the forward active mode of transistor operation, the base-collector junction is reversely polarized and the electric field is supported by the fixed charge in the depletion region. In the case of top contacted structure, there are two components of the electric field. Vertical component originates from the electric field lines which are terminated between collector donor charge and the extrinsic base acceptors, whereas horizontal component originates from the electric field lines which are terminated on the intrinsic base acceptors. Total amount of the collector charge is limited by the donor concentration in the collector and the thickness of the silicon on insulator film. This two-dimensional effect of collector charge sharing between extrinsic and intrinsic base acceptors, i.e. vertical and horizontal component of the electric field can be controlled in the way that collector becomes fully depleted and breakdown voltage improved for transistors with wider extrinsic base (wbext). At first, dependence of the BVCEO on extrinsic base width (wbext) is investigated. Simulations are done for the structures with different collector concentrations (NDC). Intrinsic base profile is kept the same in the simulations, meaning that intrinsic base is narrower and current gain (b) slightly higher for transistors with higher collector concentration. Results are shown in Fig. 4. For the doping concentrations up to 2.51017 cm-3 the effect of the BVCEO improvement can be observed if the extrinsic base width (wbext) is increased. BVCEO value saturates for extrinsic base width larger than 0.8 pm. Therefore, engineering of the breakdown voltage by the mask design is possible for extrinsic base widths up to 0.8 pm. For collector doping concentrations larger than 2.51017 cm-3, breakdown voltages are sharply reduced and 14 12 10 8 6 4 2 N dc=5x1 0 cm -CrNDC=8x10'W =1017cmJ —k- ndc=1 .5x1 0 cm /1/00=3x10 cm —Q—N =2x1017 cm"3 -o-N„=4x1017cm"3 DC DC -C— N =2.5x1017 cm"3 —r?- N =5x1017 cm": 0.0 0.5 1.0 1.5 Extrinsic Base Width, jim 2.0 Fig. 4. Dependence of BVCEO on the extrinsic base width (wbex) for different collector concentrations. 79 Informacije MIDEM 41(2011)2, str. 77-85 M. Koricic, Tomislav S.: BVceo Engineering in SOI LBT Structure with Top Contacted Base a) VCF=3 V 1x10 E »j c e a o « m - um - »^=0.2 pm - "„„=0.3 pm - "W=°-4 I" "»'»«f0-5Mm Mm ^m .5 pm 5x10 2 4 6 Collector-Emitter Voltage, V b) 2 4 6 Collector-Emitter Voltage, V for: Fig. 5. Simulation of BVCEO dependence on wbext a) Ndc=2.5-1017 cm-3, b) NDC=1.5-1017 cm3. cannot be improved by extending wbext. BVCEO simulations for collector concentrations of 2.5-1017 and 1.5-1017 cm-3 are shown in Fig. 5.a and 5.b, respectively. For collector concentration of 2.51017 cm-3 a plateau in the base current is observed for transistors with wider extrinsic base. These characteristics indicate that electric field has two peak values in the base-collector depletion region. The first peak appears at the intrinsic base-collector junction and approaches the value of the critical electric field at VCE around 3 V. Weak avalanche starts and generated holes drift to the base side reducing the base current. However, peak electric field at the intrinsic base-collector junction is not increased for VCE larger than 3 V and impact ionization is limited as indicated by the plateau in the characteristics for voltages between 3 and 7 V. This is explained by the full depletion of the collector region and the extrinsic base shielding effect. Impact ionization rate in the transistor for VCE of 3 and 9 V is shown in Fig. 6.a and 6.b, respectively. For Vce=3 V, just before full depletion of the collector, maximum impact ionization rate occurs at the intrinsic base-collector junction. When VCE is further increased up to 9 V, another region with high impact ionization rate appears E extrinsic base ___________________^ depletion region edge 1 c Imp actlcmizafcion Signed Log (cm-36-1) 24,«5 24 22 20 L8 A I .¿¿z........._ >- A' BOX peak impact ionization Vrr=9 V E extrinsic base depletion - region edge 1 c TmpactTonization Signed Log (cm-Sa-1) — 24.65 24 22 20 IB \ / BOX 2 peaks of impact ionization Fig. 6. b) Impact ionization rate for structure with NDC=2.5-1017 cm-3 at VBE=0.7 Vand a) VCE=3 V, b) Vce=9 V. in the drift region to the right side of the extrinsic base. Maximum rate occurs in the bottom part near the buried oxide interface since electrons are pushed down by the vertical component of field and current is crowded near the buried oxide interface. Since the holes generated by impact ionization drift to the base side and are injected to the emitter, a positive feedback of electrons due to transistor's current gain (b) occurs and causes BVCEO to be 2 to 3 times lower than BVcbo. Moreover, for BVCEO to occur the critical electric field has to appear along the current path since the avalanche multiplication process is initiated by mobile electrons. Simulated distribution of electric potential, field and impact ionization rate for different VCE in the plane AA' from Fig. 6. are shown in Fig. 7.a-c. From the potential distribution in Fig. 7.a it can be observed that collector is not fully depleted for VCE below 3 V. Potential is constant across neutral collector region below extrinsic base and electric field is zero. Potential drop appears across depletion region and peak electric field is placed at the intrinsic base-collector junction (Fig. 7.b). For VCE of 4 V and above, the collector under the extrinsic base is fully depleted. Characteristics of potential distribution bends and deviates from standard square function in the area below the extrinsic base and electric field magnitude in that area is reduced. Furthermore, the potential drop across the intrinsic-base-collector junction practically doesn't increase with VCE and the peak of the electric field at intrinsic base-collector junction is constant (Fig. 7.b). Since the collector charge under the extrinsic base is completely shared, there is no available charge to support increase of potential and electric field across the intrinsic base-collector junction. The rest of the potential drop appears across the drift-region on the right side with respect to the extrinsic base-collector junction. Electric field vectors for transistors with wbext of 0.5 pm and 1 |jm are shown in Fig. 8.a and 8.b, respectively. Direction of the vectors indicates the direction of the electric field, whereas length of the vectors is proportional to the magnitude of the electric field, i.e. density of the electric field lines in given points of the structure. In case of wbext=0.5 jm, a part of the field lines terminated on the intrinsic base acceptors are originated from donors in the 80 KM. KoriciC, Tomislav S.: BVceo Engineering in SOI LBT Structure with Top Contacted Base Informacije MIDEM 41(2011)2, str. 77-85 a) extrinsic base c £ o Q. ,o £ o « Si 0.5 1.0 Distance , p.m 1.5 b) E S « 3 5 O) I 5 i B o £ ,o £ o £ lu b) E £ « .3 5 O) i 5 u. .o is u j> iu 2.5x10 1 »i. ' ___________ V " /V—v=4v If"œ=2V - Miv^v I \ \ \ \\ -- I UW^ '// Myv^v ■ vc=5 v ' / 1 —^ 0.5 1.0 Distance, \un 2.5x10 5.0x10 0.0 . Wboxt _ i 1 j __,VCE=10V ■ / \ \ WW Tu— v=6V A=5V " -- ----- : ) \ \ V "TT vVvVr Vce=3V Vv-Vrrv<*=2V " 0.0 1.0 0.5 Distance, \nn Fig. 12. Electric field in the transistor 15 nm from buried oxide for structure with NDC=1.5-1017 cm-3, hE=0.2 pm and a) wbex=1 pm, b) wbex=0.5 pm. the extrinsic base shielding is not complete. Peak electric field at the intrinsic base-collector junction increases even for voltages greater than 5 V and can reach the critical value for transistor breakdown. Since part of the electric field lines originated from donors in the drift region to the right side of the extrinsic base are terminated at extrinsic base acceptors, there are more available donor charge below extrinsic base which can support horizontal electric field over the intrinsic base-collector junction. Horizontal field penetrates toward the drift region and the peak at the intrinsic base-collector junction is increased. Avalanche multiplication and transistor breakdown occur at the intrinsic base-collector junction. In addition, for larger wbext current flows over a longer distance under the influence of vertical electric field and is pushed down to the buried oxide interface. Therefore, current flows through the part of the drift region where magnitude of the electric field is smaller compared to the upper part, closer to the p+ extrinsic base region, resulting in a lower impact ionization rate. 25 20 - -O »W=0-2 -¿-«W=0-5|im =0.3 (im —Û— =0.6 (im =0.4 (im 18 nm I (im 15 - X (9 "hT 10 - 5 - 0.00 0.05 0.25 0.30 0.10 0.15 0.20 Emitter Height , |im Fig. 13. Dependence of fT on hE for different wbext. As hE is reduced, the amount of the available donor charge under the extrinsic base is reduced and voltage drop associated with vertical electric field is smaller. Therefore, a larger voltage drop appears laterally across the drift region and critical electric field for avalanche multiplication in the drift region is reached at lower VCE, causing the decrease in BVceo. For the largest values of hE, BVCEO decreases since collector is not fully depleted any more. Simulation results of fT dependence on hE for different wbext is presented in Fig. 13. For larger hE, fT is increased. As hE is increased, cross-section of the neutral collector is increased and current crowding due to vertical field influence is less pronounced. Kirk effect is pushed to higher collector currents as local current density is reduced and fT is increased. The current crowding effects are more pronounced for structures with larger wbext which can be observed as a smaller value of fT in Fig. 13. In addition, electrons are traveling through the wider depletion region increasing the associated transit time. For wbext larger than 0.5 pm the transit time through the depletion region becomes comparable to the base transit time. Furthermore, time constant associated with the collector-base capacitance and the collector resistance i.e. RCCBC is increased for larger wbext, which further reduces fT. 3.3. Link-base length dependence Influence of the link-base length (lb) on BVCEO and fT is also investigated. Emitter height (hE) is kept constant at 120 nm and collector concentration is set to 1.5-1017 cm-3. By increasing lb, thickness of the n-collector under the extrinsic base is increased and a higher collector-emitter voltage is needed to reach full depletion of the collector region. Simulation results for BVCEO dependence on lb with wbext as a parameter are shown in Fig. 14. For larger wbext, shielding by the extrinsic base field is more efficient and higher BVceo values are observed. This dependence is similar to the dependence on hE, since in both cases the amount of collector charge is changed by the variation in the thickness of the n-collector below the extrinsic base. Results of 83 M. Koričic, Tomislav S.: Informacije MIDEM 41(2011)2, str. 77-85 BVCEO Engineering in SOI LBT Structure with Top Contacted Base -O-""m=0.3 nm =0.2 nm —tî—»^=0.5 |im -—«^=0.8(1171 a Ul o i. Q 0.00 0.05 0.10 0.15 Link Base Length , |im 0.20 Fig. 14. Dependence of BVCEO on link-base length (lb) for different wb9Xt. fT dependence on lb are presented in Fig. 15. showing the similar behavior as dependence on hE. Current crowding effects are relaxed by increasing the link-base length and fT is improved. Degradation of fT by current crowding is more severe in the case of larger wbext as seen from Fig. 15. 4. Conclusions LBT structure with the base contact on top is analyzed by the device simulations. Influence of the extrinsic base width (wbext) on common-emitter breakdown voltage (BVCEO) and cutoff frequency (fT) is examined in detail. The effect of collector charge sharing can be used to obtain structures with different values of BVCEO and fT. Total amount of collector charge is determined by the collector concentration and the silicon film thickness, which can be controlled to achieve full depletion of the collector region. In case of fully depleted collector, two peaks of the electric field appear along the current path in the base-collector depletion region. The first one is at the intrinsic-base collector junction and the 0.00 0.05 0.10 0.15 Link Base Length, |im 0.20 Fig. 15. Dependence of fT on link-base length (lb) for different wb9Xt. second one in the drift region toward extrinsic collector. Extrinsic base shielding effect can be used to control the value of the peak electric field at the intrinsic-base collector junction. For smaller wbext, the horizontal field associated with the intrinsic base junction is partially shielded and the peak electric field increases with VCE. In case of larger wbext, shielding is more effective; the peak electric field increases at slower rate with VCE and approaches the critical value for avalanche multiplication at higher VCE. In both cases avalanche occurs at the intrinsic-base collector junction but BVCEO is increased for larger wbext due to smaller increase of the peak electric field with VCE. For very large wbext, horizontal field is completely shielded by the vertical field and the peak electric field at the intrinsic base junction does not increase with VCE. However, the second peak in the drift region increases with VCE and can reach the critical value for avalanche multiplication. Transistor breakdown occurs in the drift region for transistors with larger wbext. It is shown that BVCEO engineering can be achieved for wbext below 0.8 pm. Tradeoff between breakdown (BVCEO) and transistor's cutoff frequency (fT) is presented and design guidelines regarding collector concentration and transistor geometry is given. The potential of BVCEO engineering for top contacted SOI LBT structure without additional increase in cost of technology is demonstrated. References /1/ K. Cheng, A. Khakifirooz, P. Kulkarni, S. Ponoth, J. Kuss, D. Shahrjerdi, L. F. Edge, A. Kimball, S. Kanakasabapathy, K. Xiu, S. Schmitz, A. Reznicek, T. Adam, H. He, N. Loubet, S. Holmes, S. Mehta, D. Yang, A. Upham, S.-C. Seo, J. L. Herman, R. Johnson, Y. Zhu, P. Jamison, B. S. Haran, Z. Zhu, L. H. Vanamurth, S. Fan, D. Horak, H. Bu, P. J. Oldiges, D. K. Sadana, P. Kozlowski, D. McHerron, J. O'Neill, B. Doris, "Extremely Thin SOI (ETSOI) CMOS with Record Low Variability for Low Power System-on-Chip Applications", IEDM Tech. Dig., 2009, pp. 49-52 /2/ H. Nii, T. Yamada, K. Inoh, T. Shino, S. Kawanaka, M. Yoshimi, Y. Katsumata, "A Novel Lateral Bipolar Transistor with 67 GHz fmax on Thin-Film SOI for RF Analog Applications", IEEE Trans. Electron Devices, Vol. 47, No. 7, pp. 1536-1541, July 2000. /3/ M. Sun, W. T. Ng, K. Kanekiyo, T. Kobayashi, H. Mochizuki, M. Toita, H. Imai, A. Ishikawa, S. Tamura, K. Takasuka, "Lateral High-Speed Bipolar Transistors on SOI for RF SoC Applications", IEEE Trans. Electron Devices, Vol. 52, No. 7, pp. 1376-1383, July 2005. /4/ J. Cai, M. Kumar, M. Steigerwalt, H. Ho, K. Schonenberg, K. Stein, H. Chen, K. Jenkins, Q. Ouyang, P. Pldiges, and T. Ning, "Vertical SiGe-base bipolar transistors on CMOS-compatible SOI substrate", Proc. Bipolar/BiCMOS Circuits Technol. Meeting, 2003, pp. 215-218. /5/ T. Suligoj, M. Koricic, H. Mochizuki, S. Morita, K. Shinomura, and H. Imai, "Horizontal Current Bipolar Transistor (HCBT) with a Single Polysilicon Region for Improved High-Frequency Performance of BiCMOS ICs," IEEE Electron Device Lett., in press. /6/ S. A. Parke, C. Hu, P. K. Ko, "A High-Performance Lateral Bipolar Transistor Fabricated on SIMOX', IEEE Electron Device Letters, Vol. 14, No. 1, pp 33-35, January 1993. /7/ T. Shino, K. Inoh, T. Yamada, H. Nii, S. Kawanaka, T. Fuse, M. Yoshimi, Y. Katsumata, S. Watanabe, J. Matsunaga, "A 31 GHz fmax Lateral BJT on SOI Using Self-Aligned External Base Formation Technology", IEDM Tech. Dig., 1998, pp 953-956. /8/,,R. Dekker, W.T.A. v.d. Einden, H.G.R. Maas, "An Ultra Low Power Lateral Bipolar Polysilicon Emitter Technology on SOI", IEDM Tech. Dig., 1993, pp 75-78. 84 KM. Koricic, Tomislav S.: BVceo Engineering in SOI LBT Structure with Top Contacted Base Informacije MIDEM 41(2011)2, str. 77-85 /9/ G. G. Shahidi, D. D. Tang, B. Davari, Y. Taur, P. McFarland, K. Jenkins,D. Danner, M. Rodriguez, A. Megdanis, E. Petrillo, M. Polcari, and T. H. Ning, "A novel high-performance lateral bipolar on SOI", IEDM Tech. Dig., 1991 pp. 663-666. /10/ W. L. M. Huang, K. M. Klein, M. Grimaldi, M. Racanelli, S. Ra-maswami, J. Tsao, J. Foerstner, B. C. Hwang, "TFSOI Complementary BiCMOS Technology for Low Power Applications", IEEE Trans. Electron Devices, Vol. 42, No. 3, pp. 506-512, March 1995. /11/ J. M. Stork, R. D. Isaac "Tunneling in Base-Emitter Junctions", IEEE Trans. Electron Devices, Vol. 30, No. 11, pp. 1527-1534, July. 1983. /12/ E. O. Johnson, "Physical limitations on frequency and power parameters of transistors," RCA Rev., Vol. 26, pp. 163-177, 1965. /13/ J. D. Cressler, G. Niu, Silicon-germanium Heterojunction Bipolar Transistors, Artech House,2003. /14/ C.Jungemann, R.Thoma and W.L.Engl, "A Soft Threshold Lucky Electron Model for Efficient and Accurate Numerical Device Simulation," Solid-State Electronics, Vol. 39, No. 7, pp.10791086, 1996. Marko Koricic*, Tomislav Suligoj Department of Electronics, Microelectronics, Computing and Intelligent Systems, Faculty of Electrical Engineering and Computing, University of Zagreb, Unska 3, HR-10000 Zagreb, Croatia * Corresponding author. Tel.: +385-1-6129671, fax.: +385-1-6129653, e-mail address: marko.koricic@ fer.hr Prispelo: 27.05.2010 Sprejeto: 24.06.2011 85 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)1, Ljubljana STRUCTURING SOFT-MAGNETIC COMPOSITE MATERIALS M.V.Zagirnyak1, V.V.Prus1, V.P.Lyashenko1, D. Miljavec2 1Kremenchuk Ostrogradskiy State Polytechnic University,Kremenchuk,Ukraine 2University of Ljubljana, Faculty of electrical engineering, Slovenia Key words: Powder metallurgy, Soft-magnetic composites, hysteresis losses, eddy current losses, iron losses Abstract: The aim of the proposed paper is to present different procedures for preparation the mixture of soft-magnetic powder material and to show the influence of different manufacturing processes for achieving particular structures and properties of soft magnetic composite (SMC) material. The technique of SMC production with improved mechanical properties and the necessary electrical and magnetic parameters by means of powder metallurgy methods are described. A novel laminated powder structure of SMC material is developed. The content of the paper gives useful hints for specialists dealing with creation and research of new magnetic materials and magnetic systems for electric machines and power electronics. Strukturiranje mehkomagnetnega kompozitnega materiala Kjučne besede: Metalurgija prahov, mehko-magnetni kompozitni material, histerezne izgube, vrtinčne izgube, izgube v železu Izvleček: V članku so predstavljeni različni načini priprave mešanice mehkomagnetnih prahov z dodatki in vplivi različnih tehnoloških postopkov izdelave na končne lastnosti mehkomagnetnih kompozitnih (MMK) materialov. Predstavljen je merilni sistem, ki omogoča določanje magnetnih lastnosti MMK materiala. Opisane so tudi lastnosti nove lamelirane strukture MMK materiala. Vsebina članka podaja koristne napotke specialistom, ki se ukvarjajo z ustvarjanjem in raziskovanjem novih magnetnih materialov ter elektromagnetnih sklopov za elektične stroje in močnostno elektroniko. 1. Introduction Soft-magnetic composites, i.e. ferromagnetic material in the powder form are mainly made by atomization of Fe-Si compound. The material is mostly used for electric micro and small machine cores /1, 2/ and in power electronic for inductor cores. The powder can be pressed to the required shape and thus forming a magnetic core of desired geometric properties. The world production of soft-magnetic composites is limited, which results in a relatively high material cost. The price is lower regarding the 0.1 mm laminated steel, but higher as that of 0.5 mm laminated steel, traditionally used in electric machines manufacturing /3-7/. Existing production techniques ensure the required properties and characteristics of soft-magnetic composite materials due to high quality of expensive primary materials - iron powders and bonding materials, which causes a significant increase of their cost. That is why development of high-quality soft-magnetic materials and decrease of their production cost is a prospective direction of the study /8, 9/. The objective of this analysis is to improve the method of manufacturing the soft-magnetic composites samples with the required mechanical, electrical and magnetic characteristics. That include magnetic saturation Bs, residual magnetization Br, coercive force Hc, electric conductivity, iron losses Pm, mechanical strength and compactness. Taking into consideration the range of change of the analyzed parameters, it is necessary that the measuring equipment and methods of processing the measurement results take into account nonlinear properties of the magnetic material. The measurements must achieve assigned accuracy in a wide range of parameters change, including the condition of high saturation level. In this way the magnetic measurements carried out during researching are different from measurements performed throughout normative testing or during the production monitoring. 2. Preparation and fabrication of soft magnetic composite material Taking into account the peculiarities of the soft-magnetic material structure, a sequence of the main cycles of manufacturing technique by means of powder metallurgy is summarized: 1. Powder is produced by means of an electrolytic method, which provides high powder dispersion and well-developed dendrite shape of grain particles. 2. Preparation of powders for pressing, which includes their pre-firing at the temperature of 250-3500C, formation of a powder sieve structure with preset fractional dimensions, then mixing it with a lubricant and plastic bonding material ensuring maximum electrical isolation between ferromagnetic grains. Powder sieve structure is analogous to the one stated in /10, 11/. 3. Warm pressing under controlled pressure and temperature of 200-450oC, which enables plastic bonding material to cover the grain surface uniformly and to electrically insulate the grains between each other. The process of this stage also influences the formation of the grain structure into final product shape. In the frame of our research we made some specimens of SMC material in the form of rings. The rings were 86 M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko, D. Miljavec: Structuring Soft-Magnetic Composite Materials Informacije MIDEM 41(2011)2, str. 86-91 prepared for microscopic analysis and some of the results are presented below. Separate grains of different size (10+20 mm) are visible in Fig. 1. The grains are separated with inclusions layer. The separation blisters are visible, but the additives are not observed. The separate sintered grains (5+20 mm) and alloyed or sintered grains without a separating interlayer are also shown in Fig. 2. 4. Annealing at temperatures of 1150-12500C provides formation of the necessary grain structure in the product and ensures the required mechanical, electrical and magnetic properties of the soft-magnetic composite structure. For each of the mentioned cycles there are only general recommendations due to a wide range of parameters variation and different modes of performing the cycles. The task of our research is to select of all the parameters, beginning with the ones which influence the analyzed characteristics. This mainly refers to the second and fourth cycle. During the preparation for the pressing cycle the research should be focused on iron powder compositions, choice of the plastic bonding material and a lubricant to improve the necessary mechanical properties, as well as electrical and magnetic parameters. In case of high-temperature annealing it is also necessary to exactly measure the specimen temperature and cycle duration. Further results were obtained by annealing the specimen at the temperature of 2200 C. The texture of soft magnetic iron-based sample was made in this way. Uniform distribution of plastic bonding material on the grains surface was revealed (Fig. 3) by scanning the sample. The X-ray spectrum analysis of specimen (Fig. 4) shows that the electric isolation layer is spread uniformly across the grain surface. The results are presented in Fig. 4. This insulation layers decrease electric conductivity of the material and reduce induced eddy currents. Metallographic analysis was made using NIAPHOT-2 microscope (France). Fracture investigation was made by REM-106I focused beam electronic microscope (Sumy, Ukraine). Fig. 2: The separate sintered grains 5+20 micrometers and alloyed or sintered grains without separating interlayer. x-: r . ■ : m ' ; ■ ' ■ F "À ■ • . - " S V' X A . S ' r ■ / . .. r ' f* î -kM f, ■ < ' : ! y ¿KL : • _ WlJ=9 7min zo mikv Fig. 3: Uniform distribution of plastic bonding material on the grains surface Element % 2700 C Fe 0,00 99,69 2100 Tc ^um 0,31 100 1500 900 Tc 300 i Fe Tc Fe I Fe Energy (KeV) Fig. 4: The X-ray spectrum analysis of a specimen Fig. 1: Separate grains of different size (10+20 mm) with inclusions layer 87 Informacije MIDEM 41(2011)2, str. 86-91 M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko, D. Miljavec: Structuring Soft-Magnetic Composite Materials 3 Measuring system Regarding the requirements of testing equipment /12/, the use of inductive measuring procedure with alternating magnetization of samples with changing amplitude and frequency is the most reasonable one. The structure of the measuring system (MS) is shown in Fig. 5. A tested sample (TS) represents a closed magnetic system with magnetization and measuring windings. The parameters which characterize the testing system are: current i1(t), voltages u1(t) and u2(t). The signals from TS go to current CT and voltage VT2 transducers. Output signal u1(t) from off-line sinusoidal voltage source (PS) is connected to the voltage transducer VT1 and to the tested sample. Fig. 5: Block diagram of the measuring system for testing soft-magnetic composite material samples Signals from the transducers go through input/output module (IOM) to a computer, whose functions are data gathering, storage and processing. The offered MS uses certified testing module E14-440D (L-Card, Russia) as an IOM. Measuring software is realized in software environment Lab View 8.2 with the aim to achieve the reconfiguration flexibility and visualization of measurement process. Due to magnetization of soft-magnetic material in alternating magnetic fields the determination of the magnetic flux density B(t) and the magnetic field strength H(t) frequency spectrum from the linear section of magnetization up to the saturation level is required. Also, the conditions of frequency spectrum decomposition and further composition have to be formulated. Taking into consideration the above described peculiarities of the test, the determination of all the parameters was established on the base of preliminary decomposition of the measured signals applying Fourier transform. The results are used to compute the necessary parameters, such as magnetic flux density, magnetic field strength, hysteresis losses and eddy current losses. The amplitude of magnetic flux density is calculated by: 42 U2 Bm = 2k fNS (1) where U2 is the effective value of measuring winding voltage; Nms - number of measuring winding turns; Sc - mag- netic circuit core cross-section area; f - magnetization frequency. Magnetic field strength is computed by: H = (2) where I1 is the effective value of current in magnetizing winding, Nmg is the number of magnetizing winding turns and l is the average length of magnetic circuit. If B(t) and H(t) are not sinusoidal at a linear section of magnetization curve, the computation is carried out only on the basis of the first harmonic components. Total harmonic distortion of signals is estimated with the help of current i1(t) and voltage u2(t) harmonic factor: (3) where p is the higher harmonic number, k is the number of the considered harmonics, A1 and A2 are, correspondingly, effective values of the first and p-th order harmonics in signal. Losses in magnetic material are derived by N. N, —(ahpau2p +VW/4 (4) Where ai1p, bi1p, au2p and bu2p are, correspondingly, current i1(t) and voltage u2(t) signals squared components. After processing the measured values i1(t) and u2(t) a dynamic hysteresis loop is created. Instantaneous value of the magnetic field strength is found from the relation H(f) = /.,(f)A/mg//. (5) Instantaneous value of the magnetic flux density B(t) is determined by using voltage signal u2(t) by S(f) = 1 u. 2mp NmsSc ^ pto cos(pcof+(p ) (6) Where w = 2pf is signal of the first harmonic angular frequency, U2mp and jp are, correspondingly, voltage u2(t) of the harmonic components amplitude and of the initial phase obtained from the expansion into a Fourier series. A possibility to determine the relationships between magnetic losses measured at different frequencies was investigated, the aim of which was to separate them into hysteresis and eddy current losses at a constant magnetic flux. In this case the voltage amplitude must change proportionally to its frequency U . —= const f , (7) Where U, f are the amplitude and frequency of the supply voltage. The values of hysteresis and eddy current losses components are expressed by relation: Pv=P^+P,eo = Chf+Cecf2 (8) 88 M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko, D. Miljavec: Structuring Soft-Magnetic Composite Materials Informacije MIDEM 41(2011)2, str. 86-91 Where Pm, Pmh and Pmec are total magnetic losses, hysteresis and eddy current losses, accordingly; Ch and Cei corresponding coefficients. are the Specific hysteresis and eddy current losses are found from coefficients Ch and Cec in accordance with the relations: P(Jh1 50 Ch ,0/50 m rB m 1,0 (9) and P[jec1,i 2500 C. ,0/50 m 1,0 \2 (10) where pm >1,0/50 and Pmeci,0/50 are specific hysteresis and eddy current losses at the values of magnetic induction of 1T and frequency of 50 Hz, Bm is magnetic induction for which coefficients Ch and Cec were found and m is a mass of the tested sample. Then, by means of solving the equation system PMh1,0/50 +Pm8c1,0/50 = Pm1,0/50 \ / f \2 / f \(x _________ ^r) + Pued ,0/50 V—; = PM1,0/50 V3T7 bu bu bu (ii) when there are two arbitrary similar values of frequency, the values of specific magnetic losses pm10/50 at magnetic flux density of 1 T, frequency of 50 Hz and at coefficient a are defined. These results are used to define the value of total magnetic losses for the developed SMC structure in the function of magnetic flux density and frequency. 4. Production and analysis of experimental smc samples In our research, the sample produced from Hoganas (Sweden) soft magnetic powder material Somaloy 700 served as a reference. This material has one of the best electrical and magnetic properties at present. During the research process it was taken into consideration that all the mentioned properties are achieved when the composite compactness is increased and also when the additives are added to the iron powder to improve the desired properties. It means that powder can be pressed into a high-density composite, which is easily taken out of a press tool and preserves good quality of the surface. The powder was finished in the form of electrically isolated particles forming soft-magnetic material. Fatty acid amides, colophony and lump rubber were used as electrical insulators. Besides, a phosphorous containing insulating layer was also made. Many samples of SMC rings, with parameters given in Table 1, were made by various methods. Sample No.1 was made from Hoganes (Sweden) material, sample No. 2 is a laminated structure (magnetically oriented powder) with plastic bonding material based on lump rubber with annealing parameters T2 = 11500 C and t2 = 0,5 h, sample No. 3 is an isotropic structure with plastic bonding material based on colophony with annealing parameters T3 = 9000 C and t3 = 2 h, samples No. 4-5 are made as isotropic structures with plastic bonding material based on lump rubber with annealing parameters T4 = 11000 C, t4 = 1 h and T5 = 11500 C, t5 = 0,5 h. Analyzed properties are given in Table 2. Figures 6 - 10 show a family of hysteresis loops for produced samples. The excitation frequency was 50 Hz. Fig. 11 demonstrates the dependence of iron losses in the function of magnetic flux density at this frequency. Table 1: Parameters of the samples Param. Samp. No. 1 Samp. No. 2 Samp. No. 3 Samp. No. 4 Samp. No. 5 Outer diameter /cm 5,5 2 2,14 2,1 2,1 Inner diameter /cm 4,5 1,45 1,5 1,5 01,5 Height /cm 0,98 0,17 0,27 0,33 0,29 Mass /g 60 2 3 3 3 Nmg 85 65 65 65 65 Nms 100 60 100 100 100 Rmg /W 1,6* 0,15 - 0,16 0,17 Rms /W 3,5* 1,54 - 3,18 3,05 * Resistance was measured by U-I method, in other cases by measuring bridge. Table 2: Results of magnetic and electrical parameters for analyzed samples Param. Samp. No. 1 Samp. No. 2 Samp. No. 3 Samp. No. 4 Samp. No. 5 Residual magnetization /T 0,18 0,39 0,22 0,19 0,18 Coercive force /(A/m) 153 379 668 574 553 Saturation point B/H /(T/A/m) 0,42/756 0,62/795 0,31/1160 0,22/735 0,24/1075 Specific iron losses ßm=0,4T, f=50Hz* /(W/kg) 0,45 0,66 3,74 y5,5 y3,8 *For a number of samples there was not possible to determine iron losses at magnetic flux density 1T, because it was physically impossible to reach required level (sample get magnetically saturated before 1T). 89 Informacije MIDEM 41(2011)2, str. 86-91 M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko, D. Miljavec: Structuring Soft-Magnetic Composite Materials Fig. 6: Family of hysteresis loops for a sample made from Hoganes powder material Fig. 7: Hysteresis loops for sample No. 2 Fig. 8: Hysteresis loops for sample No. 3 Fig. 9: Hysteresis loops for sample No. 4 90 Fig. 10: Hysteresis loops for sample No. 5 Fig. 11: Iron losses curves pm samples f(Bm) for the analysed The results show that the nearest sample to the one made from the Hoganas company material is the sample No. 2 presenting a laminated powder structure. This structure is very promising for further research related to material structure improvement and to optimization of manufacturing process. Comparison of the gained results with the known data for the used material show that the error of the parameters measurement is within the permissible limits. Hence, the developed measuring system can be used to determine the properties of soft-magnetic composite materials. 5. Conclusions The procedure of preparing the mixture of soft-magnetic composite material was presented. The influence of different manufacturing processes in achieving particular structures and properties of SMC material was explained. Different samples were prepared and analyzed during the research. The sample produced from Hoganas ferromagnetic powder material served as a reference from the point of mechanical, electrical and magnetic characteristics. A measuring system was developed, which enables to analyze magnetic properties of developed SMC material. The system allows to measure hysteresis loops and iron losses at different excitation levels and frequencies. The results show that the sample No. 2 presenting a novel laminated M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko, D. Miljavec: Structuring Soft-Magnetic Composite Materials Informacije MIDEM 41(2011)2, str. 86-91 powder structure has properties similar to the reference one. Further research will be based on the laminated powder structures as most prospective from the point of view of obtaining the required mechanical, electrical and magnetic characteristics within the focus of material cost reduction. References /1/ H. Kuhn, B. Ferguson: Powder forging. MPIF, Princeton, NJ, 1990. /2/ M. Zagirnyak & all: Proceeding of 2000 PM2TEC International Conference, May 30 - June 3, 2000, New York, USA. /3/ D. Miljavec, B. Zidarič, M. Zagirnyak, "Soft magnetic composite in design of BLDC motor', 16th International conference on electrical machines, Conference proceedings. /Cracow/: ICEM, 2004. /4/ G. Štumberger, M. Hadziselimovic, B. Štumberger, D. Miljavec, D. Dolinar, I. Zagradišnik, "Comparison of capabilities of reluctance synchronous motor and induction motor", J. magn. magn. mater.. /Print ed./, 2006, vol. 304, iss. 2, pp. 835-837. /5/ D. Nedeljkovic, R. Fišer, V. Ambrožič, Time-optimal magnetization of inductors with permanent magnet cores = Časovno-optimalno magnetenje dušilk z jedrom iz trajnega magneta. Inf. MIDEM, 2004, 34, No. 1, pp. 32-36. /6/ M. Bugeza, R. Fišer, Estimation of linear electrical motor performance using finite element method = Vrednotenje obratovalnih lastnosti linearnih električnih motorjev s pomočjo metode končnih elementov. Inf. MIDEM, mar. 2007, 37, No. 1, pp. 42-49, /7/ L. Gašperlin, A. Černigoj, S. Markič, R. Fišer, Additional cogging torque components in permanent-magnet motors due to manufacturing imperfections. IEEE trans. magn., Mar. 2009, vol. 45, no. 3, pp. 1210-1213, / 8/ Standard Test Methods for Metal Powders and Powder Metallurgy Products. MPIF, Princeton, NJ, 1995. /9/ S. ST-Laurent, F. Chargon, Y. Thomas: Proceeding of 2000 PM2TEC International Conference, May30-June 3, 2000, New York, USA. /10/ Powder Testing Center model PTC-03DT, User's manual V-20. KSK Powder Technologies Corp., 1996. /11/ Patent of Ukraine UA 71954 C2 of 25.04.07, International application PCT/5E2004/001865, 20041215. /12/ F. Meizda. Electronic measuring equipment and measurement methods: Translation from English. - M.: Mir, 1990. - 535 p. M.V.Zagirnyak, V.V.Prus, V.P.Lyashenko Kremenchuk Ostrogradskiy State Polytechnic University, vul. Pershotravneva, 20, 39614, Kremenchuk, Ukraine, e-mail: mzagirn@polytech. poltava.ua D. Miljavec University of Ljubljana, Faculty of electrical engineering, Trzaska 25, 1000 Ljubljana, Slovenia, e-mail: miljavec@fe.uni-lj.si Prispelo: 27.09.2010 Sprejeto: 24.06.2011 91 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)1, Ljubljana ELECTROMAGNETIC ABSORBING MATERIALS Branka Mušič1, Andrej Žnidaršič2, Peter Venturini1 1Helios Domžale d.d., Domžale, Slovenija 2Nanotesla Institut, Ljubljana, Slovenija Key words: electromagnetic waves, magnetic composite, ferromagnetic materials, microwaves, measurements Abstract: Around 15 years have passed since the wireless technologies started with rapid development. During that time, different fields of electromagnetic waves have become more active. As a result of rapid advances in technology the use of wireless communication and radar systems is expanding quickly, which leads to a significant increase in the levels of background electromagnetic (EM) radiation /1/. To avoid potential health effects from high exposure to electromagnetic waves, unnecessary EM waves should be eliminated to protect human bodies, especially expectant mothers and children /2/. In European Pre-standard ENV 50166-2:1995 - Human exposure to electromagnetic fields - High frequency, is stated that electromagnetic fields interact with the human body and other systems through a number of physical mechanisms. Therefore, it is necessary to protect all of these systems. As mentioned in ENV standard, it is recognized that additional considerations have been made by some countries, regarding the reference levels as minimum requirements in certain frequency ranges. Those considerations resulted in additional reference margins /3/. This is the reason why is nowhere a background of electromagnetic waves including many reviews of diverse articles on topics of electromagnetic materials. We decided to bring out that summery to deliver this diversified information to all types of readers, both technical and non-technical. Absorberji elektromagnetnega valovanja Kjučne besede: elektromagnetno valovanje, magnetni kompoziti, feromagnetni materiali, mikrovalovi, meritve Izvleček: Okoli 15 let je minilo, odkar se je začel hiter razvoj brezžične tehnologije. Med tem časom so postala bolj aktivna tudi različna območja elektromagnetnih valov. Kot rezultat hitrega razvoja tehnologije, se je uporaba brezžičnih komunikacij in radarskih sistemov naglo razširila. To vodi v znatno povišanje koncentracije elektromagnetnega sevanja v okolici /1/. V izogib potencialnemu vplivu, pri visoki izpostavljenosti elektromagnetnemu valovanju, bi morali elektromagnetno sevanje omejiti oz. odstraniti, da bi zaščitili ljudi, posebno matere in otroke /2/. V evropskem pred-standardu ENV 50166-2:1995 - Izpostava ljudi elektromagnetnemu polju - Visoke frekvence, je navedeno, da elektromagnetno polje vpliva na človeško telo in druge sisteme s številnimi fizikalnimi mehanizmi. Zato je potrebno vse te sisteme zaščititi. Kot je zapisano v ENV standardu, so bile v nekaterih državah narejene dodatne raziskave, o minimalnih varnostnih zahtevah v zvezi z izpostavljenostjo v določenih frekvenčnih območjih. Ugotovitve teh raziskav so vodile v določenih državah do dodatnih, strožjih ukrepov. /3/. Zgoraj omenjena dejstva in ugotovitve so povod, da smo v tem članku opisali ozadje elektromagnetnega valovanja in pregled različnih člankov na temo elektromagnetnih materialov. 1. Introduction We have a different type of electromagnetic sources. The first one is natural source. Electromagnetic fields are present everywhere in our environment. Electric fields are produced by the local build-up of electric charges in the atmosphere and released with thunderstorms. Electromagnetic fields at low frequencies exist whenever a positive or negative electrical charge is present. Besides natural sources, the electromagnetic spectrum also includes fields generated by human-made sources. Various kinds of higher frequency radiowaves are used to transmit information - whether via TV antennas, radio stations or mobile phone base stations and radar produce high RF fields. And for example in the workplace: computers, fax machines, fluorescent lights, printers, scanners, telephone switching systems, electrical instruments, electric engines and other electrical devices. Additional sources are household appliances, such as stereo systems, refrigerators, blend- ers, portable heaters, clothes washers and dryers, coffee makers, vacuum cleaners, toasters, microwave ovens and others. Like electric fields, magnetic fields are strongest close to their origin and rapidly decrease at greater distances from the source. Materials, such as building materials and trees, provide some shielding capability. Therefore, the electric fields from power lines outside the house are reduced by walls, buildings, and trees. Conductors, such as metal, provide very effective shield. However, magnetic fields are not blocked by common materials, buildings' walls, for example. The protection from electromagnetic radiation is an up to date theme. Since the discovery that electromagnetic fields can affect our health, researchers have investigated these phenomena in vivo and in vitro, in animals /4-6/ and humans /7-13/. 92 B. Music, A. Znidarsic, P. Venturini: Electromagnetic Absorbing Materials Informacije MIDEM 41(2011)2, str. 86-91 A multiphase study has been performed to find an effective protection and method to evaluate systems and patients exposure to electromagnetic field (EMF). We have two typical ways. We can shield from EMF or use the absorbing method. But the shielding materials cannot eliminate or weaken EMI radiation, and moreover the reflected wave may interact with the incident wave, which causes disturbance to other devices. Another way is usage of electromagnetic absorbers like multipart materials that absorb incident electromagnetic radiation in limited wave spectrum. Only by using electromagnetic wave absorbing materials and transferring the electromagnetic energy to other forms can the radiation be attenuated to the furthest extent /14/. In physics, absorption of electromagnetic radiation is procedure by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy, for example, to heat. According to the wave absorption mechanism, traditional wave absorbers can be divided into three types as electric loss, magnetic loss and dielectric loss materials. Carbon materials and conductive polymers are electric attenuation absorbents, which have higher electric loss tangent (tan 8S) and the electromagnetic energy is mainly attenuated as resistor. Ferrites and fine powder are magnetic loss absorbents, which have higher magnetic loss (tan 8J, and attenuate and absorb electromagnetic energy by polarisation mechanisms such as hysteresis loss and magnetic domain resonance. Metal fibre and many ceramic materials such as barium titanate belong to dielectric loss absorbents, which mainly attenuate electromagnetic energy by electronic and ionic polarisation. Most of the metal based absorbants used in cement matrix composites are steel fibres and ferrites, for which Japanese institute have made many studies /15/. The reflection curve of an electromagnetic absorber is a function of a complex interplay between the permittivity, the permeability and the thickness of the absorber. From material point of view both permeability and permittivity can be varied, whereas with design an additional degree of freedom is obtained (thickness). incident wave absorptive layer Fig. 1: Scheme of a simple, one-layer absorber. Absorptive layer can be made from either dielectric or soft-magnetic materials with appropriate loss tangent. Usually the absorber layers are made from composite materials, mixtures of dielectric (carbon black, aluminum flakes...) and/or soft-magnetic (ferrites, carbonyl iron) particles in some matrix; however, excellent absorbers can be made from ferrite ceramics for use at lower frequencies. Since every material has advantages and disadvantages, the selection of materials is difficult and depends on actual application. Characterization of absorbers can be made directly with standardized measurements of reflection in free space or indirectly through measurements of constituent materials' electromagnetic properties. The latter method is greatly used in the designing phase, since in general the reflection from the absorber can be analytically calculated from known materials' characteristics and geometry /1/. For simple one-layer absorber with metal backing the equation for reflection is: fi(cffi)=20-log 10 iAtan(kd)-'\ iAtan(kd)+'\ A-je. k = — -^¡xe c where m and e are complex permeability and permittivity respectively, f is the frequency of the incident EM wave, c is the speed of light in vacuum, and d is the thickness of the absorbing layer. From this we can see that the key parameters that can be varied are complex permeability and permittivity of material and thickness of layer, whereas frequency of the incident EM wave is external factor. An example of the reflection curve as a function of frequency is shown in Figure 2. m S..15 c 0 1 J-20 | \ R \ 11 t mm 0.5 1 1.8 2 frequency (GHz) Fig. 2: Reflection of one-layer absorber as a function of frequency. Reflection levels -10 dB and -20 dB correspond to 10% and 1% reflection of energy respectively. 93 Informacije MIDEM 41(2011)2, str. 92-96 B. Music, A. Znidarsic, P. Venturini: Electromagnetic Absorbing Materials In order to characterize the absorber properties three key parameters are used: width of absorption band Df, frequency range where reflection is below some level, usually -10 dB (10% reflection) or -20 dB (1% reflection); frequency of minimum reflection fmjn; and level of reflection at fmn, Rmnn. An evaluation of quality of the reflection curve is rather arbitrary and depends on the desired frequency range and level of absorption, which usually differ for various applications. 2. Review of existing experimental work Electromagnetic materials are advantageous for applications of microwave and millimeter wave protection. Many characteristic can influence on materials absorbing properties. In present article I will mention some significance evaluation of efficiency of electromagnetic absorbing materials dependent on chemical structures, concentrations, sizes, shapes and syntheses. Different characteristic of electromagnetic materials with various methods have been studied by many authors /16-21/. Research group from India investigated the microwave absorption of M-type hexaferrite-polymer composites prepared with different ferrite ratios of 50 wt.%, 60 wt.%, 70 wt.%, 80 wt.% in polyurethane matrix. Investigated have been in 8,2-12,4 GHz frequency range. It was found that the absorption properties in the composites are greatly improved with increasing ferrite contents in the polymer matrix. The composite with 80 wt. % ferrite content has shown a minimum reflection loss of -24,5 dB at 12 GHz with a -20 dB bandwidth over the extended frequency range of 11-13 GHz in a quite thin sample with a thickness of only 1,6 mm /22/. The permittivity, permeability and absorbing properties of coatings with carbonyl-iron particles as absorber and epoxy-silicone resins as matrix was also represented. The properties were investigated with different weight concentrations in the frequency range of 2-18 GHz. The plate shape (flake) particles of a carbonyl-iron have a size of 2-5 pm and about 1 |jm thicknesses. The content of carbonyl-iron particles was 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, 70 wt.% and 75 wt.%. Both the values of the real and imaginary parts of the permittivity increase with the carbonyl-iron weight concentration. The initial permeability increased more or less linearity to 70 wt. % and rapidly increased from 70 to 75 wt. %. A minimum reflection loss value of -42,5 dB was obtained at 10,6 GHz for the containing 55 wt. % carbonyl-iron. When the coating contains 75 wt.% carbonyl-iron particles, the region of reflection loss values less then -10 dB is below 2 GHz /23/. Lots of studied showed that the microwave properties of electromagnetic absorber materials depend on particle size, shape and granulate. The goal of next work was investigation of absorbing properties for different shapes and aggregated states of carbonyl-iron particles dispersed in epoxy resin matrix at various volume concentrations of 0,3-0,6 vol.%. The de-aggregated flake-shaped carbonyl-iron particles have higher permeability, lower permittivity and better absorbing properties in the frequency range of 2-18 GHz then aggregated sphere-shaped particles. The flake-shaped composite for 60 vol.% has the minimum reflection loss value -12,2 dB at 4,4 GHz for a 1 mm thickness layer /24/. Spherical and monodisperse Co20Ni80 particles were prepared, in the micrometer and sub-micrometer size range. The particle are with a mean diameter 1,4 jm, a narrow size distribution, and a low degree of agglomeration. The particles of second sample are smaller with a mean diameter 0,33 jm. Particles were randomly dispersed in epoxy resin. Microwave properties of composites were measured in 0,1-18 GHz. The micrometer size particles exhibit a permeability curve with a single resonance bands. The submicrometer size particles exhibit a behavior with three resonance bands /25/. Some studies indicate that the hexagonal strontium ferrite is also good microwave absorber /26-27/. It is more adaptable than ferrites with spinel and garnet structure in case of a high frequency. However, susceptibility of ferrites at these frequencies is low, which makes it difficult to further improve their microwave absorption property. The susceptibility of metal powder is higher /28-29/ and such materials are typically used for frequencies up to 30 GHz. In literature we can find researchers reports that plated layer on absorbers materials can improve absorbing properties of electromagnetic radiation. Modifying the properties of one material by coating it with another type of material has been a popular approach widely documented in the literature /30-34/. Shanghai's Jiao Tong University worked on the synthesis of anatase coated barium ferrite composite particles suitable for microwave absorption applications. They reported on core-shell (barium-anatase) structures of magnetic particles that exhibit unique magnetic properties. The results of prepared sample with 75 wt.% ferrite in epoxy resin, in the frequency range of 2-12 GHz show that the titanium coverage on barium ferrite has a great influence on its microwave properties. The maximum reflection loss was obtained at the Ti:Ba ratio of 1:10 /35/. It is found that the complex permeability of the sintered ferrite Ni2Y (Y-type hexagonal ferrite, Ba2Ni2Fe12O22) is higher than that of the ferrite composite Ni2Y. Because the ferrite composite is composed of the ferrite particles coated with non-magnetic layer, its complex permeability is decreased. The complex permeability of the ferrite absorber is dependent upon frequency, but the complex permittivity is nearly constant. In those ferrite bodies most of the loss is mainly attributed to magnetic loss, while their dielectric loss is negligible /36/. China's Shanghai University has reported that the best way to solve this problem is fabricating the composite of ferrite and metal powder efficiently. They prepared a new type of Ni-coated strontium ferrite magnetic nanosized powder (Ni/ 94 B. Mušič, A. Žnidaršič, P. Venturini: Electromagnetic Absorbing Materials Informacije MIDEM 41(2011)2, str. 92-96 SrFe12O19) with electroless plating enchased by ultrasonic wave at room temperature. Their results show that the powder possesses excellent microwave absorption properties. The microwave absorption properties were measured from 5 to 15 GHz. They shown that the maximum microwave loss of the composite powder reach -41,3 dB. The bandwidth with the loss above -10 dB was 8 GHz /37/. Japan scientists already presented a NiZn ferrite spin sprayed film, 3 |jm thick, as a material exhibiting strong magnetic loss (reaching 67% attenuation of magnetic field at 3 GHz) and also reflection loss weak (smaller then 7%) enough to be practically applied to noise suppressors operated up to several GHz /38/. Development of new magnetic materials and their understanding on a smaller - nano scale is a cause of advance in many areas of materials science. For a variety of important applications show promise for future, because of its large specific surface areas and the nano particles are much less then the incident wavelength, so it can greatly reduce the reflection from the surface, which make better impedance matching /39/. Researchers from Tokyo University achieved similar results by combining reverse-micelle and sol-gel techniques to create high-performance millimeter wave (30-300 GHz) absorber composed of a series of e-AlxFe2-xO3 nanomagnets with particles size between 25 nm and 50 nm. These materials show natural resonance in the region up to 182 GHz, which is the highest frequency for magnetic materials. The absorption peaks in millimeter wave range for samples: 30 wt. % (x = 0), 26 wt. % (x = 0,06), 24 wt. % (x = 0,09), 30 wt. % (x = 0), 29 wt. % (x = 0,21), 29 wt. % (x = 0,3) and 34 wt. % (x = 0,04) were observed at 112, 125, 145, 162, 172 and 182 GHz, respectively /40/. The a-Fe/C(amorphous) and Fe3C(amorphous) nanocomposites have been prepared. The epoxy resin compacts with 40 vol.% a-Fe/C(amorphous), and ^^(amorphous). were characterized in frequency range of 0,05-26,5 GHz. Powders provided good electromagnetic wave absorption performances (reflection loss < -20 dB) in ranges 4,3-8,2 GHz, and 9-26,5 GHz over absorber thicknesses of 1,8-3,3 mm and 1-2,4 mm, respectively /41/. Behave of materials and device structures whose characteristic feature sizes are on nanometer scale are reported /42/. There are numerous electromagnetic materials on the market designed for a wide variety of applications. This short section show that is in specified field of work many different opportunities for further investigations exist for absorbing materials. 3. Conclusion Electromagnetic materials are becoming more and more important for our society. We can find applicability in many different fields, for example in electronics or medicine. Apply directly to casing 1 irinril In Coupled li nes Reduction ol cou pling Fig. 3: Examples of applications soft-magnetic composites for reduction of electromagnetic noise. Which type of electromagnetic protection should be used depends on the requirements and technical limitations. With electromagnetic absorbing materials we can decrease the effects of EM waves on the human body and other systems. Different scientists from around the word are looking for better and better materials with new, different properties, with higher effectiveness and efficiency. However, as long as there is a possibility to do something better, a need for new materials and their new properties research will exist. Literature /1/ Bregar V.B., Znidarsic A., Lisjak D., Drofenik M., Development and characterization of an electromagnetic absorber. 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E., Porter, W. E., & Bolton, N. E. (1978). The biological effects of magnetic fields on man. J. Am. Ind. Hyg. Assoc., 39, 1-11. /13/ Smith, C.W., & Best, S. (1989). Electromagnetic man. New York: St. Martins Press. /14/ N. Dishovsky, M. Grigorova. On the correlation between electromagnetic waves absorption and electrical conductivity of carbon black filled polyethylenes. Mater. Res Bull 35(3), pp. 403-409 (2000) /15/ Guan, S. Liu, Y. Duan, J. Cheng. Cement based electromagnetic shilding and absorbing building msterials. Cement & Concrete Composites 28, pp. 468-474 (2006) /16/ Hribernik B., »Uvod v magnetne materiale«, 1. izdaja Tehniška fakulteta VTO-ERI, Maribor 1991 /17/ Hamler A., Hribernik B., »Elektrotehnični materiali«, Založniška dejavnost FERI, Tiskarna tehniških fakultet, 2005 /18/ Fiorillo F., »Measurement and characterisation of magnetic materials«, Elsevier Academic Press, 2004 /19/ Berttoti G., Hysteresis in magnetism for physicist, material scientists, and engineers, San Diego; Academic Press, cop. 1998 /20/ Wohlfarth E.P., Handbook of Magnetic Materials; Elsevier: Amsterdam, 1980; Vol.2 /21/ Committee on identification of research needs relating to potential biological or adverse health effects of wireless communications devices, National Research Council. Identification of Research Needs Relating to Potential Biological or Adverse Health Effects of Wireless Communication; National Academies Press: WA, 2008 /22/ S.M. Abbas, A.K. Dixit, R. Chatterjee, T.C. Goel. 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Mater 247:249 /29/ Zhou P.H., Xie L.J., lang D.F., Chen L., Zhao X.Q. (2005) J Magn. Magn. Mater 292:325 /30/ Quirantes A., Plaza R., Delgado A.; J. Colloid Interface Sci. 189 (1997) 236-241 /31/ Ishikawa T., Matijevic E., Langmuir 4 (1988) 26-31 /32/ Zabetakis D., Dinderman M., Schoen P., Adv. Mater. 17 (2005) 734-738 /33/ Watson S., Beydoun D., Amal R., J. Photochem. Photobiol. A: Chem 148 (2002) 303-313 /34/ Park O.K., Kang Y.S., Colloid Surface A 257-258 (2005) 261-265 /35/ Tang X., Zhao B.Y., Tian Q., Hu K.A. Synthesis, characterization and microwave absorption properties of titania-coated barium ferrite composites. Journal of Physics and Chemistry of Solids 67 (2006) 2442-2447 /36/ J.Y.Shin, J.H.Oh, »The Microwave Absorbing Phenomena of Ferrite Microwave Absorbers«, IEEE Transaction on Electromagnetic Compatibility, vol. 29, No. 6 (1993). /37/ Pan X., Qiu J., Gu M. Preparation and microwave absorption properties of nanosized Ni/SrFe12O19 magnetic powder. (2007) J. Mater Sci 42:2086-2089 /38/ Kondo K., Chiba T., Ono H., Yoshida S. Conducted noise suppression effect up to 3 GHz by NiZn ferrite film plated at 90 C directly onto printed circuit board. (2003) Journal of Applied Physics Vol.93, No.10, Parts 2,3. /39/ P. Tablot, A.M. Konn, C. Brosseau, Electromagnetic characterization of fine-scalecomposite materials, J.Magn. Mater 249(3):481-5 (2002). /40/ A. Namai, S. Sakurai, .M. Nakajima, T. Suemoto, K. Matsumoto, M. Goto, S. Sasaki, S. Ohkoshi. Synthesis of an Electromagnetic Wave Absorber for High-Speed Wireless Communication. JACS ARTICLES, Published on Web 12/30/2008 /41/ J.R.Liu, M. Itoh, T. Horikawa, E. Taguchi, H. Mori, K. Machida. Iron based carbon nanocomposites for electromagnetic wave absorber with bandwidth in GHz range. J. Appl. Phy. A 82, pp.509.513 (2006). /42/ P. Tablot, A.M. Konn, C. Brosseau. Electromagnetic characterization of fine-scale particulate composite materials. Journal of Magnetism and Magnetic Materials, 249, pp. 481-486 (2002). mag. Branka Mušič Helios Domžale d.d., Količevo 2, 1230 Domžale, Slovenija e-mail: branka.music@helios.si Telefon: + 386 1 722 40 09; Fax: + 386 1 722 43 50 Doc. dr. Andrej Žnidaršič Nanotesla Institut, Stegne 29, 1521 Ljubljana e-mail: andrej.znidarsic@kolektor.com Telefon: + 386 1 583 31 22; Fax: + 386 1 583 32 31 Doc. dr. Peter Venturini Helios Domžale d.d., Količevo 2, 1230 Domžale, Slovenija e-mail: peter.venturini@helios.si Telefon: + 386 1 722 43 73; Fax: + 386 1 722 43 50 Prispelo: 27.05.2010 Sprejeto: 24.06.2011 96 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana ANALYSIS OF METAMATERIAL ATTACHMENT FOR EM ABSORPTION IN HUMAN HEAD Mohammad Rashed Iqbal Faruque1, Mohammad Tariqul Islam 2, Norbahiah Misran1, 2 1Dept. of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Selangor, Malaysia. institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, Selangor, Malaysia. Key words: antenna, human head model, lossy-Drude model, metamaterials, specific absorption rate (SAR). Abstract: The reducing specific absorption rate (SAR) with metamaterials attachment is investigated in this paper. The finite-difference time-domain method with lossy-Drude model is adopted in this analysis. The technique of SAR reduction is discussed and the effects of attaching location, distance, and size of metamaterials, perfect electric conductor (PEC), and materials on the SAR reduction are investigated. Metamaterials have achieved a 41.47% reduction of the initial SAR value for the case of 1 gm SAR. These results suggest a guideline to choose various types of metamaterials with the maximum SAR reducing effect for a phone model. Vpliv dodatka metamateriala na absorpcijo EM valovanja v človeški glavi Kjučne besede: antena, model človeške glave, lossy-Drude model, metamateriali, specifična absorbcijska stopnja (SAR) Izvleček: v članku opišemo zmanjšanje parametra SAR ( specifična absorbcijska stopnja ) z dodatkom metamateriala. Analizo smo opravili z modelom Drude in uporabo končnih diferenc v časovni domeni. Opisana je tehnika zmanjšanja parametra SAR , raziskani so vpliv lokacije, oddaljenosti in velikosti metamaterialov ter vpliv popolnega električnega prevodnika (PEC) in vrste metamaterialov na zmanjšanje SAR. Z uporabo metamaterialov smo dosegli 41,47 % zmanjšanje začetne vrednosti SAR, ki je bila 1gm SAR. Ti rezultati pomenijo neko vrsto smernic za izbiro materialov za mobilne telefone, ki najbolj zmanjšujejo parameter SAR. 1. Introduction With the rapid and ever more widespread use of mobile phones, public concern regarding the possible health hazards has been growing, which brings an increased requirement on electromagnetic (EM) absorption for mobile phones. The basic parameter in the EM absorption is defined in terms of the specific absorption rate (SAR), or the absorbed power in unit mass of tissue /1/. The SAR is generally evaluated using either phantom measurement or computer simulation. The finite-difference time-domain (FDTD) method is currently the most widely accepted means for the SAR computations /2/. The interaction of handset antennas with the human body is a great consideration in cellular communications. The user's body, especially the head and hand, influence the antenna voltage standing wave ratio (VSWR), gain, and radiation patterns. Furthermore, thermal effects, when tissues are exposed to unlimited electromagnetic energy, can be a serious health hazard. Therefore standards organizations have set exposure limits in terms of SAR /3, 4/. SAR is a measure of the rate at which radio frequency (RF) energy is absorbed by the body when exposed to a radio-frequency electro-magnetic field. SAR is used to measure exposure to fields between 100 kHz and 10 GHz /5-8/. It is commonly used to measure power absorbed from mobile phones and during MRI scans. The value will depend on the geometry of the part of the body that is exposed to the RF energy, and on the exact location and geometry of the RF source. Cellular phone protection and the enforcement of pertinent exposure standards are issues in the current media, and regulatory agencies are motivated to assure that compliance testing is acceptable. IEEE Standard 1528 /3/ and IEC 62209-1 specify protocols and process for the measurement of the peak spatial-average SAR induced inside a simplified model of the head of users of hand held radio transceivers (cellular phones). For example, the SAR limit specified in IEEE C95.1: 1999 is 1.6 W/kg in a SAR 1 gm averaging mass while that specified in IEEE C95.1: 2005 has been updated to 2 W/kg in a 10 gm averaging mass /4/. This new SAR limit specified in IEEE C95.1: 2005 is comparable to the limit specified in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. The interaction of the cellular handset with the human head has been investigated by many published papers considering; first, the effect of the human head on the handset antenna performance including the feed-point impedance, gain, and efficiency /7-9/, and second, the impact of the antenna EM radiation on the user's head due to the absorbed power, which is measured by predicting the induced SAR in the head tissue /10-13/. The most used method to solve the electromagnetic problem in this area is the finite-difference time-domain (FDTD) technique /13-14/. Although, in principle, the solution for general geometries does not require any additional effort 97 M. R. I. Faruque, M. T. Islam, N. Misran: Informacije MIDEM 41(2011)2, str. 97-104 Analysis of Metamaterial Attachment for EM Absorption in Human Head with respect to the standard method, the technique requires the definition of a discretized space by assigning to each cell its own electromagnetic properties, which is not an easy process /15-18/. Specifically, the problems to be solved in SAR reduction need a correct representation of the cellular phone, anatomical representation of the head, alignment of the phone and the head, and suitable design of metamaterials. In /12/,/19/ a perfect electric conductor (PEC) reflector was placed between a human head and the driver of a folded loop antenna. The result showed that the radiation efficiency can be enhanced and the peak SAR value can be reduced. In /15/, /20/ a study on the effects of attaching conductive materials to cellular phone for SAR reduction has been presented. It is shown that the position of the shielding material is an important factor for SAR reduction effectiveness. There is a necessity to make an effort for reducing the spatial peak SAR in the design stage of the ferrite sheet because the possibility of a spatial peak SAR exceeding the recommended exposure limit cannot be completely ruled out. Metamaterials have inspired great interest due to their unique physical properties and novel application /14/, /21/. Metamaterials denote artificially constructed materials having electromagnetic properties not generally found in nature. Two important parameters, electric permittivity and magnetic permeability determine the response of the materials and metamaterials to electromagnetic fields. The negative permittivity can be obtained by arranging the metallic thin wires periodically /22-24/. On the other hand, an array of split ring resonators (SRRS) can exhibit negative effective permeability. The designed SRRS operated at 1.8 GHz and were used to reduce the SAR value in a lossy material. In /12/, the designed SRRS operated at 1.8 GHz were used to reduce the SAR value in a lossy material. The metamaterials are designed on circuit board so it may be easily integrated to the cellular phone. Simulation of wave propagation into metamaterials was proposed in /13/. The authors utilized the FDTD method with lossy-Drude models for metamaterials simulation. This method is a helpful approach to study the wave propagation characteristics of metamaterials /25/ and has been more developed with the perfectly matched layer (PML) and extended to three-dimension problem /26/. At first materials are placed between the antenna and a human head, and then replaced by a metamaterial. In order to study the SAR reduction of an antenna operated at the GSM 900 band, the effective medium parameter of metamaterials is set to be negative at 900 MHz Different positions, sizes, and negative medium parameters of metamaterials for SAR reduction effectiveness are also analyzed. This paper is structured as follows. Section II describes the numerical analysis of the handset together with the SAM phantom head, and the FDTD method is used with positive meshing techniques for quick and correct analysis. will be described in Section II. The SRRS structure, design and simulation of metamaterials results are explained in Section III, Section IV concludes the paper. 2. Simulation model and numerical techniques A. Model Description The simulation model which includes the handset with PIFA type of antenna and the SAM phantom head provided by CST Microwave Studio® (CST MWS) is shown in Fig. 1. A complete handset model composed of the circuit board, LCD display, keypad, battery, and housing was used for simulation. The relative permittivity and conductivity of individual components were set to comply with industrial standards. In addition, definitions in /5-6/, /20/ were adopted for material parameters involved in the SAM phantom head. In order to accurately characterize the performance over a broad frequency range, dispersive models for all the dielectrics were adopted during the simulation /5/. Fig. 2 shows the dispersive permittivity of the liquid in the SAM phantom head for simulation. In Fig. 2, Eps' and Eps" represents dielectric dispersion fit Debye 1st order and 2nd order respectively. The electrical properties of materials used for simulation are listed in Table 1. A PIFA type antenna constructed in a helical sense operating at 900 MHz for GSM application was used in the simulation model. In order to obtain a high-quality geometry approximation for such a helical structure, a predictable meshing scheme used in the FDTD method usually requires large number of hexahedrons which in turn makes it extremely challenging to get convergent results within reasonable simulation time. Fig. 1. Complete model used for simulation including handset and SAM phantom head. 98 M. R. I. Faruque, M. T. Islam, N. Misran: Analysis of Metamaterial Attachment for EM Absorption in Human Head Informacije MIDEM 41(2011)2, str. 97-104 Electric Dispersion :2nd Order Model (Fit) Eps" Eps' 1.5 2 2.5 3 Frequency/GHz 3.1 Fig. 2. Dispersive permittivity of the liquid in the SAM phantom head used for simulation. Table 1: Electrical properties of materials used for simulation Phone Materials £r o(S/m) Circuit Board 4.4 0.05 Housing Plastic 2.5 0.005 LCD Display 3.0 0.02 Rubber 2.5 0.005 SAM Phantom Head Shell 3.7 0.0016 Liquid @ 900MHz 40 1.42 B. Numerical Technique CST MWS, based on the finite integral time-domain technique (FITD), was used as the main simulation instrument. A non-uniform meshing scheme was adopted so that the major computation endeavor was dedicated to regions along the inhomogeneous boundaries for fast and perfect analysis. Fig. 3 shows the mesh for two cut planes of the complete model indicating the area with denser meshing along the inhomogeneous boundaries. The minimum and maximum mesh sizes were 0.3 mm and 1.0 mm, respectively. A total of 2,097,152 mesh cells were generated for the complete model, and the simulation time was 1163 seconds (including mesh generation) for each run on an Intel Core ™ 2 Duo E 8400 3.0 GHz CPU with 4 GB RAM system. The analysis workflow started from the design of the antenna with complete handset model in free space. The antenna was designed such that the S11 response was less than -10 dB over the frequency band of interest. The SAM phantom head was then included for SAR calculation using the standard definition as /7/ SAR- 2p where E is the induced electric field (V/m), p is the density of the tissue (kg/m3), and s is the conductivity of the tissue (S/m). The resultant SAR values averaged over 1 gm and 10 gm of tissue in the head were denoted as SAR 1 gm and SAR 10 gm, respectively. These values were used as a benchmark to appraise the effectiveness in peak SAR reduction. Fig. 3. Mesh view for two cut planes of the complete model showing the non-uniform meshing scheme adopted for simulation. Fig. 4 shows a portable telephone model at 900 MHz for the present study. It was considered to be a quarter wavelength PIFA antenna mounted on a rectangular conducting box. The conducting box was 10 cm tall, 4 cm wide, and 3 cm thick. The PIFA antenna was located at the top surface of the conducting box. Fig. 4. The head and antenna model for SAR calculation. The SAM head model was considered for this research where it consists about 2,097,152 cubical cells with a resolution of 1 mm. The FDTD method was employed in the numerical analysis. Its discretized formulations were derived from the following Maxwell's time-domain equations: m 81 n0nr \i0\ir e0Er (1) (2) where a* =eon0nI.' and a =coe0E" were added for treating magnetically and electrically lossy materials, respectively. A space domain enclosing the human head and the phone model 5 is also shown in Fig. 5. The time step was set to where c 99 M. R. I. Faruque, M. T. Islam, N. Misran: Informacije MIDEM 41(2011)2, str. 97-104 Analysis of Metamaterial Attachment for EM Absorption in Human Head is the speed of light, to guarantee the numerical stability. The time-stepping was performed for about eight sinusoidal cycles in order to reach a steady state. To absorb the outgoing scattered waves, the second order Mur absorbing boundaries acting on electric fields were used. An antenna excitation was introduced by specifying a sinusoidal voltage across the one-cell gap between the helix and the top surface of the conducting box. The antenna output power is defined as Pout Pabs Pferr Pad = - f cLeI2 dv+ — f (cL£f+c1/i|2)dv 2 J ra 1 1 2 tyf 1 1 117 + -Re(¡ExH*.n.ds) 2 Js (3) where Pabs is the power absorbed in the head with a volume of Vh, Pferr is the power dissipated in the ferrite sheet with a volume of Vf, and Prad. is the power radiated to the far-field, which can be calculated by integrating the normal component of the Pointing vector E x H* over a surface S completely surrounding the head/phone model configuration. 3. Reduction of sar using metamaterial The SAR in the head can be reduced by placing a metamaterial between the antenna and the human head. The metamaterial is on a scale less than the operating wavelength. The structures are resonant due to internal capacitance and inductance. The stop band can be designed at the operation bands of cellular phone radiation. The metamaterial are designed on a printed circuit board so it may be easily integrated to the cellular phone. By arranging sub-wavelength resonators periodically we get the metamaterial structure. A. SRRS Structure We establish that metamaterials can be used to reduce the peak SAR 1 gm and SAR 10 gm in the head from the FDTD analysis. In this section, metamaterials operated at the 900 and 1800 MHz bands of the cellular phone were considered. The metamaterials can be attained by arranging SRRS periodically. The SRRS structure consists of two concentric rings of conductive material. There is a gap on each ring, and each ring is situated opposite to the gap on the other ring. The schematics of the SRRS structure that we used in this study as shown in Fig. 6. The significant frequency of the SRRS can be varied toward a higher or lower frequency band by appropriately choosing these structure parameters. B. SRRS Design To construct the metamaterial for SAR reduction, we proposed one model of resonators namely the SRRS as shown in Fig. 6. We design the resonators for operation at the 900 MHz bands. The SRRS contains two square 100 rings, each with gaps appearing on the opposite sides /14/. The SRRS was introduced by Pendry et al. in 1999 /16/ and subsequently used by Smith et al. for synthesis of the first left-handed artificial medium /21/. A lot of effort worldwide has been spent studying single negative metamaterials (SNMs), double negative metamaterials (DNMs), their properties /5-7/, /21/, applications in antennas /7/, /21-22/, and other microwave devices /21- 23/. In Fig. 6, the structures of resonators are defined by the following structure parameters: the ring thickness c, the ring gap d, the square ring size l, the split gap g, and c0 is the speed of light in free space. The resonant frequency f is very sensitive to small changes in the structure dimensions of the SRRS. The frequency response can be scaled to higher or lower frequency by properly choosing these geometry parameters. After an extensive simulation study, we have found out a closed-form formula for the resonant frequencies of the SRRS: W = kl2[4(2^-C°)-g]e:/2 (4) The SRRS is resonating at approximately half the guided-wavelength of the resonant frequency. There are two resonances from the split rings. We have given the formula for the resonance of the outer split ring, which has a lower resonance frequency. Fig. 6. The structure of the SRRS. Numerical simulations that predict the transmission properties depend on the various structure parameters of this system. Simulations of this complex structure are performed with the FDTD method. To construct the resonators for SAR reduction, let us assume that the resonators lie in the xz plane, as shown in Fig. 7. The EM wave propagates along the y direction. The electric polarization is kept along the z-axis and magnetic field polarization is kept along x axis. Periodic boundary conditions are used to reduce the computational domain and an absorbing boundary condition is used at the propagation regions. The total-field/scatter-field formulation is used to excite the plane wave. The regions M. R. I. Faruque, M. T. Islam, N. Misran: Analysis of Metamaterial Attachment for EM Absorption in Human Head Informacije MIDEM 41(2011)2, str. 97-104 inside of the computational domain and outside of the SRRS were assumed to be vacuum. we found that when the thin wires operate at 900 MHz, the size is also too large for practical application. Because the SRRS structures are significant due to internal capacitance and inductance, they are on a scale less than the wavelength of radiation. In this study, it is established that the SRRS can be designed at 900 MHz while the size is similar to that of a cellular phone. Table 3: Comparisons of peak sar at 900 mhz without metamaterial z » Periodic Boundary Condition Absorbing Boundary Condition Tissue SAR value (W/kg) SAR value for /7/ 2.17 SAR value for /14/ 2.43 SAR value for /20/ 2.28 SAR value this work for 1 gm 2.002 Absorbing Boundary Condition Periodic Boundary Condition Fig. 7 Top view of a plane wave incident on the periodic (SRRS). From this study, it is found that both of the two incident polarizations can produce a stop band. As shown in /23-26/, the stop band corresponds to a region where either the permittivity or permeability is negative. When the magnetic field is polarized along the split ring axes, it will produce a magnetic field that may either oppose or enhance the incident field. A large capacitance in the region between the rings will be generated and the electric field will be powerfully concentrated. There is strong field coupling between the SRRS and the permeability of the medium will be negative at the stop band. Because the magnetic field is parallel to the plane of SRRS, we imagine the magnetic effects are small, and that permeability is small, positive, and slowly varying. In this condition, these structures can be viewed as arranging the metallic wires periodically. The stop bands of the SRRS are designed to be at 900 MHz and 1800 MHz. The periodicity along x, y, z axes are Lx = 63 mm, L = 1.5 mm, and Lz = 63 mm respectively. On the other hand, to obtain a stop band at 1800 MHz, the parameters of the SRRS are chosen as c = 1.8 mm, d = 0.6 mm, g = 0.6 mm, and r = 12.9 mm. The periodicity along the x, y, z axes are Lx = 50 mm, L = 1.5 mm, and Lz = 50 mm, respectively. Both the thickness and dielectric constant of the circuit boards for 900 MHz and 1800 MHz are 0.508 mm and 3.38 mm respectively. After properly choosing geometry parameters, the SRRS medium can display a stop band around 900 MHz and 1800 MHz. SRRS producing a good stop band and size are large. Therefore, SRRS are suitable for mobile phones as per size and recital point of view. We have tried to use a high impedance surface configuration /22/ to reduce the peak SAR. However, we found that when these structures operate at 900 MHz, the sizes of these structures are too large for cellular phone application. A negative permittivity medium can also be constructed by arranging the metallic thin wires periodically /24/. However, Fig. 8. The antenna, metamaterials, and head model for SAR reduction. C. Results The designed SRRS were placed between the antenna and the human head. Fig. 8 shows the head used in SAR simulation. The antenna was arranged parallel to the head axis. The distance between the antenna and head surface was 20 mm. The SAR value was calculated for an antenna output power equal to 600 mW. The calculated peak SAR 1 gm without metamaterials was 2.002 W/kg. The SAR simulation is compared with the results in /7/, /14/, /20/ for validation, as shown in Table III. The distance between the antenna feeding point and edge of the metamaterials was A= 3 mm. The size of the metamaterials in the xz plane was 48 mm x 48 mm and the thickness was 6 mm. The SAR value and antenna performance with the metamaterial were analyzed. To evaluate the power radiated from the antenna, the source impedance (ZS) was assumed to be equal to the complex conjugate of the free space radiation impedance (ZS= 102.14+ j83.78W). The source voltage (VS) was chosen to obtain a radiated power in free space equal to 600 mW ( VS = -Jo.6.8.Rm.). When analyzing the effect of 101 M. R. I. Faruque, M. T. Islam, N. Misran: Informacije MIDEM 41(2011)2, str. 97-104 Analysis of Metamaterial Attachment for EM Absorption in Human Head the metamaterials and the human head on the antenna performance, the source impedance and source voltage were fixed at the ZS and VS values. The power radiated from the antenna was evaluated by comparing the radiation impedance in this situation (ZR= Rr+ jXR) and used the following /19/ equation: R R ZD+Z< - 'SI (5) The total power absorbed in the head was calculated by , 2 -abs iLa E\ dv (6) Table 4: Effects of metamaterial on antenna performances and sar reduction at 900 mhz ZR (G) Pr (mW) Pabs (mW) SAR 1 gm (W/Kg) Without material 63.39+j94.53 600 268.83 2.002 1, E= -3 51.93+j99.79 514.6 211.95 1.0897 1, e = -5 54.12+j95.25 532.8 238.45 1.5635 1, e = -7 59.25+j96.14 541.9 251.34 1.732 Different negative medium parameters for SAR reduction effectiveness were analyzed. We placed negative permittivity mediums between the antenna and the human head. First, the plasma frequencies of the mediums were set to be wpe = 9.309X109 rad/s, which give mediums with m = 1 and e = -3 at 900 MHz. The mediums with larger negative permittivity m = 1, and e = -5; m = 1, and e = -7 were also analyzed. We set re = 1.2 X 108 rad/s, suggesting the mediums have losses. Numerical results of SAR value and antenna performance are given in Table IV. The peak SAR 1 gm becomes 1.0897 W/kg with m = 1 and e = -3 mediums. Compared to the condition without metamaterials, the radiated power is reduced by 13.9% while the SAR is reduced by 53.35%. With the use of and mediums, the SAR reduction effectiveness is decreased. However, the radiated power from the antenna is less affected. Comparisons of the SAR reduction effectiveness with different positions and sizes of metamaterials were analyzed. Simulation results are shown in Table V. In case 1, the distance between the antenna and metamaterial was changed from 3 mm to 6 mm. In case 2, the metamaterial thickness was reduced from 6 mm to 3 mm. It is found that both the peak SAR 1 gm and power absorbed by the head increase with the increase of distance or the decrease of thickness. In case 3, the size of the metamaterial was increased from 48 mm X 48 mm to 56 mm X 56 mm. It can be noted that the peak SAR 1 gm is reduced significantly while the dreadful conditions on the radiated power due to metamaterial is insignificant. To further examine whether the metamaterial affected the antenna performance or not, the radiation pattern of the PIFA antenna with the m = 1 and e = -3 metamaterial was analyzed. The use of metamaterials was also compared with other SAR reduction techniques. A PEC reflector and a ferrite material are commonly used in SAR reduction. The PEC Table 5: Effects of sizes and positions of metamaterial on antenna performances and sar values Zr (G) Pr (mW) P,bs (mW) SAR 1 gm (W/Kg) Without material 63.39+j94.53 600 268.83 2.002 ^=1, e =-3 51.93+j99.79 514.6 211.95 1.0897 Case 1 58.37+j95.35 539.4 253.53 1.6105 Case 2 62.19+j96.86 557.2 258.74 1.6893 Case 3 69.15+j107.38 573.33 216.83 1.2346 reflector and ferrite sheet were analyzed. The relative permittivity and permeability of the ferrite sheet were e =7.0-j0.58 and m =2.83-j3.25, respectively. Numerical results are shown in Table VI. A PEC placed between the human head and the antenna is studied. It can be found that the peak SAR 1 gm is increased with the use of a PEC reflector. This is because the EM wave can be induced in the neighbor of a PEC reflector due to scattering. When the size of PEC sheet is small compared to the human head, the head will absorb more EM energy. Similar results of peak SAR increase with PEC placement were also reported in /14/. The use of a ferrite sheet can reduce the peak SAR 1 gm effectively. However, the degradation on radiated power from the antenna is also significant. In addition, compared to the use of a ferrite sheet, the metamaterials can be designed on the circuit board so they may be easily integrated to the cellular phone. Table 6: Comparisons of sar reduction techniques with different materials Zr (G) Pr (mW) SAR 1 gm (W/Kg) 1, e = -3 51.93+j99.79 514.6 1.0897 PEC reflector 66.83+j32.23 509.3 4.6803 Ferrite sheet 169.33+j153.69 519.3 1.043 To study the effect of SAR reduction with the use of metamaterials, the radiated power from the PIFA antenna with m = 1 and e = -3 mediums was fixed at 600 mW. Numerical results are shown in Table VII. It is found that calculated SAR value at 900 MHz, without the metamaterial, is 2.002 W/kg for SAR 1 gm and with the metamaterial, the reduction of the SAR 1 gm value is 1.1917 W/kg. The reduction is 41.47%. Table 7: Effects of comparisons with metamaterials on sar reduction (pr = 0.5 w for 900 mhz) 900MHz SAR 1 gm value for /14/ SAR 1 gm value in this work Without material m =1, e =-3 2.43 2.002 1.89 1.1917 From simulation results, the metamaterials can reduce peak SAR effectively and the antenna performance can be less affected. The metamaterials are resonant due to internal capacitance and inductance. The mediums will display a stop band with a single negative medium parameter. Besides, we need to be more careful in taking the square root of negative 102 M. R. I. Faruque, M. T. Islam, N. Misran: Analysis of Metamaterial Attachment for EM Absorption in Human Head Informacije MIDEM 41(2011)2, str. 97-104 m and e of metamaterial. For example, instead of writing, e = -3 we write e = 3 exp (ip). When the mediums with m = 1 and e = -3 are studied, the propagation constant becomes (3 = w-J|ie|i0e0 = ®V3^i0£0 X exP (¡^2)= (opii0e0 {J) The propagation constant is imaginary and the fields inside the metamaterials will fall off exponentially with the distance from the surface. Fig. 9 shows the simulated SAR distribution for an optimal metamaterial. Fig. 9. SAR distributions after reduction using the metamaterial. This work has achieved 41.47% of SAR reduction whereas the design reported in /14/ achieved 22.63% respectively. This is achieved due to the consideration of different density, different antenna, different size of metamaterial, different type of conductivity and it is because the electromagnetic source is being moved away from the head. 4. Conclusions The EM absorption between an antenna and the human head with metamaterials has been discussed in this paper. Utilizing metamaterial in the phone model a SAR value is achieved of about 0.693 W/kg for SAR 10 gm and 1.1917 W/kg for SAR 1 gm is achieved. Based on the 3-D FDTD method with lossy-Drude model, it is found that for the both cases of peak SAR 1 gm and SAR 10 gm of the head can be reduced by placing metamaterials between the antenna and the human head. Numerical results can provide useful information in designing communication equipment for safety compliance. Acknowledgement The authors would like to thank Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia (UKM) and the MOSTI Secretariat, Ministry of Science, Technology and Innovation of Malaysia, e- Science fund: 01-01-02-SF0566, for sponsoring this work. References /1/ Report of Telecommunications Technology Council for the ministry of Posts and Telecommunications, Deliberation no. 89, "Radio-Radiation Protection Guidelines for Human Exposure to Electromagnetic Fields," Tokyo, 1997. /2/ K. S. Kunz and R. J. Luebbers, "The finite difference time domain method for electromagnetic," Boca Raton, FL, CRC, 1993. /3/ IEEE C95.1-2005. "IEEE Standards for safety levels with respect to Human Exposure to Radio Frequency Electromagnetic fields,3KHz to 300GHz," Institute of Electrical and Electronics Engineers, Inc. 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Mohammad Rashed Iqbal Faruque1, Mohammad Tariqul Islam2, Norbahiah Misran1,2 1Dept. of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia. 2Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia. rashedgen@yahoo.com, titareq@yahoo.com, bahiah@vlsi.eng.ukm.my Prispelo: 06.02.2010 Sprejeto: 24.06.2011 104 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana DESIGN AND DEVELOPMENT OF COMPACT MICROSTRIP ANTENNAS FOR PORTABLE DEVICE APPLICATIONS 1Ahmed Toaha Mobashsher, 2Mohammad Tariqul Islam, 1Norbahiah Misran 1Dept. of Electrical, Electronic and Systems Engineering, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia Key words: HCASA, SSA, COMPACT ANTENNA, portable device applications Abstract: During the last decade, wireless communication system developments have been a major motivator of compact antenna research, most particularly for portable device applications. This paper addresses to a development procedure of designing compact antennas. By a careful observation at the current distribution and folding of slots after calculating the resonating slot length, the compactness of microstrip antenna can be achieved. Two compact slot antennas, namely hollow central annular slot antenna (HCASA) and spiral slot antenna (SSA) are designed and prototyped for validation, where the experimental result agrees well the simulation. The overall volume of these antennas are respectively 0.11 Xox0.11 Xox0.005Xo and 0.08Xox0.08Xox0.005Xo where Xo is the free space operating wavelength, that concludes the reduction of 75 and 86.2% of antenna volume comparing that of an ordinary annular slot antenna operating at the same frequency. Načrtovanje in razvoj kompaktnih mikrostrip anten za uporabo v prenosnih napravah Kjučne besede: HCASA, SSA, kompaktna antena, uporaba za prenosne naprave Izvleček: Razvoj brezžičnih komunikacijskih sistemov je v zadnjem desetletju bil glavna gonilna sila razvoja kompaktnih anten večinoma za uporabo v prenosnih naprav. V članku je opisan postopek razvoja načrtovanja kompaktnih anten do katerih pridemo z analizo tokovne porazdelitve ter rezonančne dolžine in položaja rež. Načrtali in probali smo dva tipa kompaktnih anten z režami, kjer se simulacije ujemajo z eksperimentalnimi rezultati: HCASA -antena s sredinskim obročem in SSA - spiralna antena. Prostornini teh anten so 0.11Xox0.11Xox0.005Xo in 0.08Xox0.08Xox0.005Xo, kjer Xo predstavlja valovno dolžino v vakumu; to pomeni zmanjšanje za 75% in 86,2 % volumna navadnih anten, ki delujejo na enaki frekvenci. 1. Introduction In modern mobile and wireless communications systems, there is a increasing demand for compact antennas that can be easily integrated into the portable devices. In this regard, microstrip antennas are highly preferred because of their characteristics such as ease of fabrication and integration, compactness and low profile. Basically the compactness of the antenna is a trade-off between the size and the performance of the antenna due to the fact that antenna performance is bound with the fundamental limits based on the size of the antenna. This is especially true in the field of radio communications, where reducing the size of an antenna leads to smaller and light-weight systems, thereby enhancing portability and minimizing electromagnetic interference with other electronic devices. One way for miniaturization is to alter the geometry of the antenna, such that the electrical length of the current path is increased /1/. Nevertheless, the size of microstrip patch antenna can be reduced with a dielectric of the high relative dielectric constant. But the dielectric caused the degradation of gain and radiation efficiency, thus we need to develop methods for miniaturization through the structural change of the patch. There are some methods reported to minimize the antenna resonating at some lower frequencies. It has been shown that resonant patch antennas can be miniaturized using artificial magneto dielectrics /2/. Further compactness of these antennas has also been achieved through loading, using dielectrics, resistors, shorting pins, or meandering microstrip lines /3/. However, such loadings can increase their loss, complication or fabrication cost. In portable devices there is PIFA, IFA and printed monopole or loop antennas are very promising and widely used as compact antennas /4-6/. However, such internal mobile antennas usually excite large surface currents on the system ground plane of the mobile phone, which functions as an effective radiation portion. An isolation distance of about 7mm or larger between the antenna and the nearby conducting elements or electronic components in the mobile phone is usually required to avoid large degradation effects on the performances of the internal antenna, due to the large excited surface currents 105 Informacije MIDEM 41(2011)2, str. 105-113 A. T. Mobashsher, M. T. Islam, N. Misran: Design and Development of Compact Microstrip Antennas for ... on the system ground plane, especially in the region near the internal antenna /7,8/.This is a big limitation for the portable devices. In this paper, a design procedure of compact antennas is proposed which is based on calculating the resonating slot length. The process starts from a conventional annular ring slot antenna and ends with two proposed compact antennas. All of the antennas are designed for operation at 920 MHz. On the basis of the current distribution, it has been shown that the antenna slots can also be folded or coiled in spiral to produce lower frequencies in a low profile by maintaining almost the same slot length. However some impedance matching measures has to be taken to optimize the antennas in desired low frequencies. From the view of simplicity and compactness, these miniaturized antennas are also very prognosticating as they do not need big ground planes to provide good radiation patterns. 2. Theoretical evaluation Slot antennas are attractive because they are easy to analyze, design and fabricate. Their radiation pattern can be bidirectional or unidirectional and is possible to have radiation at low elevation angles for an annular slot of the geometry shown in the co-ordinate system of Figure 1 in an infinite and perfectly conducting ground plane, magnetic surface current of the annular distribution can be given by where Ea is the aperture electric field and n is the unit vector normal to the aperture. The general equations for the-far electric field components Eq and & can be written as /9/ Ea ■ jk e -jkR 271 a+W 4n R J J{M(p)sin(f-^)- 0 a E* = jk e -jkR 2% a+W ,cos0. J J{M(p)cos((|)'-<|)) 471 R 0 a + ') sin(<|)' - i>)}.ejpksme cosi^].pdpdi)' where k is the free space propagation constant. + Let us consider the point of observation P is represented in the co-ordinate by R, 0 and f; the inner radius of the annular slot as a; the width of the slot as W and where Ef and Ep are respectively the slot electric field components in f and 0 directions. For a narrow (W <<10) and fixed annular slot the field component equations can be solved as Slot Fig. 1. Annular-slot Geometry kW e~JkR Eq = -jnE0a—--——cos«<|)./JI(a£sin6) W e~jm Ea =j"nE0a--sinn(]).cote.^(izA:siiie) 2 R -Jn{ak sin6) where J'(ak&wQ) = ———m _ " d(aksmQ) However, for a constant slot width and when 0.0015 ^ w/ 10 ^ 0.075 and 3.8 ^ er ^ 9.8 an approximation can be provided to obtain the guided wavelength of the resonance by using Bessel functions as /10/ Xg -Xc -0.01 In 0.9217- 0.277 ln(er) + 0.0322 \0.5 + 0.453 \K j 4.6- 3.65 e^(9.06-100»X) Nevertheless, the dominant TMn1 mode resonant frequency, fn of the slot antenna is determined by nc Jn ~ 2nfi R„ Here, Rm is the mean radius of the annular ring slot, n is the mode number of resonance, eeff is the relative efficiency of the slot line and c is the speed of light in free space. Usually, the resonant frequencies are mainly determined by the mean radius of the annular slot. The mean radius can be defined by Rm = (R, + R0)/2 where, R, is the inner radius and R0 is the outer radius of the annular ring slot. 3. Antenna miniaturization In order to explain the miniaturization technique of the microstrip antenna using current distribution trace, a conventional annular ring slot microstrip antenna has been discussed with a center frequency of 920MHz, shown in Figure 2. The antenna is designed on FR4 substrate of er = 4.4 and tanS =0.02. The antenna dimensions are tabulated 106 A. T. Mobashsher, M. T. Islam, N. Misran: Design and Development of Compact Microstrip Antennas for Informacije MIDEM 41(2011)2, str. 105-113 in Table I. A symmetrical external 50Q microstrip feeding is introduced to provide impedance matching and excite the conventional annular ring slot. As the fundamental TM11 mode is excited the corresponding equation to determine resonance can be found as f =___ '1L +R, * It is noted that this equation is valid as long as a thin substrate is used for the annular ring antenna. Table 1 Design parameters of the conventional annular slot antenna (a) L W Ro R SW FW FL FD 70 70 33 30 3 3 16 35 (a) b) c) 0.9 0.92 0.94 Frequency (GHz) Fig. 2. The (a) top view, (b) bottom view and (c) return loss of conventional annular slot antenna b) Fig. 3. Current distribution at 920MHz of (a) conventional annular ring slot antenna and (b) annular ring slot antenna with side feeding As presented in Figure 2(b), the antenna shows a -10 dB bandwidth of 18.2 MHz having central frequency of 920 MHz. In order to understand the effect of the antenna feeding position, the feeding is displaced from the middle to FD = 52.5 mm. Providing proper impedance matching by varying the feeding length, the modified antenna achieves resonance at 920MHz. As seen from the current distribution pattern of the antennas in Figure 3, at resonance frequency, the current densely flows at the edges of the annular slots, while in middle portions of the circular disks the currents are null. The current flows toward the microstrip feeding at the outside portion of the slot and at the inside portion of the slot the current traces flows from the feeding. These two traces produce null current at mean slot length of about 2nRm/2~0.5Xg where guided wavelength at resonance frequency, = -JEeff and effective dielectric constant zeff +^2=2.7; which makes the current paths symmetrical to the microstrip feeding line /11/. Shifting the antenna feeding line in the upper portion of the antenna increases current density in that region. This introduces the initial step of miniaturization, by cutting the modified antenna in the middle and taking the high 107 Informacije MIDEM 41(2011)2, str. 105-113 A. T. Mobashsher, M. T. Islam, N. Misran: Design and Development of Compact Microstrip Antennas for ... c) Fig. 4. Current distribution at 920MHz of (a) half annular ring slot antenna (b) half double annular ring slot antenna and (c) half double annular ring slot antenna without central disk current density portion into account, which is pictured in Figure 4(a). Moreover, in order to match the impedance accurately 2.5mm width is shorten from the half circular antenna, which makes the mean circumference of the antenna =(2-7t ■31.5)/2-2-2.5 = 0.47Air where 1g is the wavelength at the slot at the resonance frequency. This resolves that the minimized slot antenna fed by a microstrip transmission line radiates as a magnetic dipole /12/. Nevertheless, it is exhibited that the current density largely flows on the two edges of the dipole like slot and in the central portion of the antenna current strength gradually decreases. So as the next step of miniaturization, shown in Figure 4(b), another half ring slot of 2mm is cut on the ground plane providing 1mm distance between the slots. This half double annular ring slot antenna (HDARSA) also resonates at the desired frequency of 920MHz. However, this also shows null current traces in the central portion of the disk. So for the sake of miniaturization, in the next step, depicted in Figure 4(c), the half circular disk is etched from the ground and it was observed that the current distribution remains almost similar. However, the length of feeding line is extended for better impedance matching in the resonating frequency. In the following sections two miniaturized antennas are proposed and their optimization process is presented and discussed. 4. Proposed geometry description The configurations of the two compact microstrip slot antennas are illustrated in Figure 5. Both of the antennas are designed on a low cost substrate, FR4 of height hs = hc = 1.6mm with relative permittivity er = 4.4 and loss tangent tanS =0.02. The first antenna is a hollow central annular slot antenna (HCASA), which consists of an annular slot with the central portion etched out from the ground of antenna. And second spiral slot antenna (SSA) having an optimized spiral slot in the ground plane. Both of the antennas are fed by 50Q microstrip lines, which give suitability for the antennas to embed with the circuit boards. The antenna design parameters of the microstrip-fed miniaturized antennas are given in Table II. In Table III the comparative volume of the miniaturized antennas are also mentioned. (a) b) L. (c) d) Fig. 5. Structure of proposed hollow central annular slot antenna (HCASA) top and side view (a & b), spiral slot antenna (SSA) top and side view (c & d) 108 A. T. Mobashsher, M. T. Islam, N. Misran: Design and Development of Compact Microstrip Antennas for Informacije MIDEM 41(2011)2, str. 105-113 Table 2: Design parameters of the miniaturized antennas Hollow Central Annular Slot Antenna (HCASA) Lc Wc Rci Rc2 SWc SSc FWc FLc FDc e e 35 35 17 14 3 1 3 10 17.5 45 60 Spiral Slot Antenna (SSA) Ls Ws RS1 Rs2 sws SSs FWS FLS FDc 26 26 11.7 2 3 1 3 7 13 Table 3: Comparative volume of the miniaturized antennas Hollow Central Annular Slot Antenna (HCASA) Spiral Slot Antenna (SSA) Antenna Volume (mm) 35x35x1.6 26x26x1.6 Antenna Volume Relative to the Free Space Operating Wavelength (Xo) 0.11 \ x0.11 \ x0.005 \ 0.08 \ x0.08 \ x0.005 \ 5. Analytical study & optimization The goal of the performed analytical parametric studies is to facilitate more elaboration of the design procedures and optimization processes for miniaturized antennas. Various parameters are investigated to examine the effects of the antenna parameters on resonant frequency, return loss as well as the impedance bandwidth of the antenna. This study covers the formulation of the antenna design, influences of varying the slot lengths on resonant frequency and return loss, the implication of choosing the separation angle for the design, the consequence of changing the offset angle for achieving the best optimized minimized antennas. For better convenience of the effect on the performance of the antenna upon changing the parameters, only one parameter is changed at a time, while keeping others unchanged. 5.1. HCASA The mean circumference of the HCASA slot can be illustrated as, C(0) = 2nr - Qr Applying this equation for the designed antenna we get, for 0 = p/8 and r = 15.5, the length C(0) = 91. The length of the circular slot is approximately 0.46lg, where 1g is the wavelength at the slot at the resonance frequency. This properly corresponds to the miniaturized half circular antennas discussed previously discussed. Nevertheless, the angles for the two ends of the slots are optimized to achieve proper impedance matching for the best performance of the antenna. Figure 6 shows the relationship between the angle of separation, 0 between the two edges of the slot with the resonant frequency and return loss at the respective frequency. It is seen that the resonant point of the antenna increases almost linearly when the angle, 0 is increased gradually. In the same time, the respective return loss does not behave so monotonously. This is because of the impedance matching of the antenna with feeding strip. In spite of the ripples we can derive a merely straight line for the relation of 0 and return loss. However it is also observed (not shown in graph) that the bandwidth of the antenna increases with increase of the angle. The reason for this phenomenon can be attributed to the relatively electrically large aperture of the antenna as the resonance frequency also increases, having the physical dimensions of the overall patch remaining almost the same. In this design, the angle, 0 = 45° is taken as the optimized one for attaining the resonance frequency of 920MHz. 45 65 Separation Angle (6) Fig. 6. The effect of different separation angel, 0 on resonant frequency and return loss 10 20 30 40 50 60 70 Offset Angle (By) Fig. 7. The relationship between the offset angle, 0f with resonance and return loss The offset angle of the slot edge, 0f from the line of feeding affects the impedance matching and the resonance frequency dramatically, which is verified by the exhibited graphs of Figure 7 with different values of 0f angle providing other shapes and parameters unchanged. Figure 9 shows 109 A. T. Mobashsher, M. T. Islam, N. Misran: Informacije MIDEM 41(2011)2, str. 105-113 Design and Development of Compact Microstrip Antennas for ... that the antenna meets the desired resonance frequency 920MHz when 0f = 10o with a low return loss, which implies a defective impedance matching of the antenna. However the best impedance matching is achieved when 0f = 45o but the resonating frequency is over 920MHz. When 0f = 60o, the resonance falls once again at 920MHz with a better impedance matching and this is taken as the optimized parameter. Nevertheless, with the increasing of when 0f, the resonance point still goes to higher frequencies with a gloomy return loss. 5.2. SSA Spiral arm can be represented as /13/, r(j) (js < j < je) a j + ra Here, r(j) is the radial distance from the origin to the arbitrary point on the centre line of the spiral, a is the spiral constant, j is the winding angle, js is the spiral start angle, je is the spiral end angle, and ra is the radial distance from the origin to the initial point of the spiral line. The mean arc length of the Archimedean spiral C(js, je) in polar coordinates between js and je is: C(qs,, header files (.h) can be added with the instruction %. Instructions have to be added in the core of BlockTypeSetup function in TLC file. Calls to initialization routines of hardware moduls can be added to the function start. In the function outputs, function call to the custom C function can be noticed, which is a result of previous C-MEX S-function generation. - The model is loaded in Simulink. A project with source and header files in CCS is generated. We look for a custom C function file in the project and uncomment the commented parts of code. - Added part of the code can be debuged as well and in that way the success of operation of the added module can be prooved in the CCS After the mentioned algorithm, a modul that receives values from an external AD converter and a modul for communication with a personal computer were added. Modul for AD conversion was developed, since that kind of system was 128 N. Semenič, A. Sarjaš, R. Svečko, A. Chowdhury: Design and Implementation of Rapid Control Prototyping System ... Informacije MIDEM 41(2011)2, str. 122-131 not possible to realize with basic blocks, mainly because of the complexity of communication through the SPI bus. Modul for communication with a personal computer enables an easier supervision over the sent and received data, since a duration time needed for the execution of the specific part of code can be exactly measured with the CPU timer in the DSP. 5. Example of test plant control A test plant consists of a mechanical framework, pendulum, electrical motor, feeder and a processor with the adapted electrical circuit. The concept of stabilization of an invert pendulum presents a mounted arm on an electrical motor, where at the end, on the bearings, a pendulum is mounted. With a suitable control of the electrical motor, we can affect the position of the arm and indirectly so, the position of the pendulum. State space controller have been designed to achieve stabilization. That way we need the information on all of the internal states od the system. These are the speed and angle of the pendulum and the speed and position of the arm. The speed of pendulum is calculated on the basis of pendulum angle change. Position and speed of the arm is measured with the encoder. Potentiometer is set behind the bearing of the pendulum and it is supplied by voltage of 5 V. The signal in the frame of 0-5 V presents the position of the pendulum 0-360 Due to the nonlinearity of the potentiometer, it is possible to measure in a range of 0-340 ° with ± 3 ° of tolerance. Encoder modul enables measuring of the position and the speed of the arm with event signals received from encoder. Event represents every positive or negative front of the encoder output QEPA or QEPB signals, that are dislocated r1 r2 Sum1 ■ r3 r4 f<) Idle Task Speed Low RPM Speed RPM Arm angle deg Pendulum speed RPM Pendulum angle deg Inverted Pendulum Send data ,0 pc Fig. 5.1: RCP for inverse rotation pendulum among each other by 90 ° (Figure 3.1). Encoder has 1000 lines. Taking that in consideration, due the possibility to register positive and negative fronts, it can be registered 4000 events in one turn. An electrical circuit is located on the external circuit board, which adapts levels of voltage supply between the processor and the motor as well as between the processor and the sensores. On the ecternal circuit board, there is a H-bridge that provides up to 6 A of current for the motor. H-bridge is controled by the processor by the principle of pulse width modulation (PWM). 6. Design of the core program for stabilization of the inverted pendulum A row of hardware interrupts were realized in the DSP. Every interrupt has its own specific time deterministic task. In the center portion of the program core, which is presented by an infinite while loop, functions are carryed out that take care of sending the measuring resaults to the personal computer. Synchronization of the external AD converter with the DSP, is carryed out through an external interrupt. When AD has the current measured data available in the memory data registry, the external pin DRDY falls to 0. This happens exactly evey 0,01 s, which is the sampling time. This event triggers the hardware interrupt in which, through the SPI bus, value of the data register of AD converter is obtained. In that interrupt, the value of the register QUTMR of encoder module is adapted as well. That is the encoder modul timer which is responsible for triggering of the encoder interrupt,. that is also triggered every 0,01 s, respectively the sampling time. With the adaptation of the encoder timer, the synchronization of the encoder interrupt routine with the interrupt of the AD converter is reached. In the interrupt of the AD converter, with the appropriate setting of CpuTimer0 value, the synchronization with the system interrupt is also performed. Through the proper synchronization encoder interrupt occures just before the interrupt of AD converter. System interrupt of Simulink follows both interrupts. The position and the speed of the arm is obtained during the interrupt of the encoder. In the interrupt of the AD converter, the information on the position of a pendulum is obtained, the speed of the pendulum is calculated on the basis of the change of the pendulum position. In the system interrupt, the chosen regulator is calculated and an adequate PWM exit is set (Figure 5.1) The system is designed so that the interrupt of AD converter has a priority over the encoder interrupt. 129 N. Semenič, A. Sarjaš, R. Svečko, A. Chowdhury: Informacije MIDEM 41(2011)2, str. 122-131 Design and Implementation of Rapid Control Prototyping System ... 7. Designing the state space controllers For the control system, inverted pendulum two type of state space controllers were designed. The first type of state space controller was designed through pole placement technique (PPT) and the second type with optimization of the quadratic continuous-time cost functional ( LQR). A mathematical model of third and fourth order was used for design of controllers. Model was adapted from work /12/. Pole placement controller was designed with the closed-loop poles assignment and Matlab command »acker«. LQR controller was designed with the expression »lqr« and the appropriate weightening (Q and R) matrices. Taking into consideration that the controllers were designed for a linear system and tested on a nonlinear model in Simulink, where was checked whether the solutions suit the stability criteria. With the simulations, we could also test until which point the system was stable, if pendulum had deviated. 8. Resaults During the design of PPT controllers, a third order model was used, since the control upon the position of the arm is not significant for the stabilization of the pendulum. During the realization of the controller with the setpoint, a fourth order model and the position of the arm was used as a reference signal. LQR controller was designed with the systems of third and fourth order. As results show, the best designed controllers are those, which are designed with the third order system. That is to say, the controllers do not demand the stabilization of pendulum in exact defined point of the position of the arm. If we compare these two controllers to the controller with the setpoint, it is established that in the maximal deviation of angle of the pendulm, it swings almost twice the amount. It is comprehensive that by the setpoint controller considerations not only about the angle of the pendulum but also the position of the arm like setpoint is taken into account. Pendulum angle using third order pole placement controller Pendulum angle using fourth order setpoint-crossbar position 0 10 20 30 40 SO 60 70 80 90 100 Time [s] Pendulum angle [°] 20 30 Time [s] Fig. 8.2: Controller with the setpoint-crossbar position Pendulum angle using third order LQR controller E 0 < - Pendulum angle [°] 0 10 20 30 40 50 60 70 80 90 100 Time [s] Fig. 8.3: Third order LQR controller Pendulum angle using fourth order LQR controller Fig. 8.4: Fourth order LQR controller Two linear quadratic controllers were calculated. A third order system was used to design the first one. With the second one, a fourth order system and the position of the arm as a reference position were used. If we compare the measurements with previously mentioned controllers, it is visible at first sight that both positions of the pendulum were steadier. If we compare the strenghtening of both regulators with the ones before, it is stated that they are much more sensitive to the position of the pendulum. Fig. 8.1: Pole placement controller 130 N. Semenic, A. Sarjas, R. Svecko, A. Chowdhury: Design and Implementation of Rapid Control Prototyping System Informacije MIDEM 41(2011)2, str. 122-131 9. Conclusion The goal of our work was to carry out the system for rapid prototyping in the Matlab/Simulink environment. It is confirmed that the newer version of Matlab has numerous advantages with the development of Code Legacy Tool modules and the expanded set of TIC2000 library. Individual basic moduls in the library are more complex and enable more precise hardware settings, that are very welcomed since they enable improved functionality. With that, an in-depth knowledge of hardware DSP moduls is neccessary. The system of rapid prototyping, with rich library collection in Simulink, presents a simpler and faster way of adaptation of algorithms that are in the form of block models and a simplified algorithm testing on real plants. The system of rapid prototyping was successfully tested with the stabilization of the rotary inverted pendulum. 10. Acknowledgment Operation part financed by the European Union, European Social Fund. References /1/ L. Baotai, Z. Rongxiang, Rapid Control Prototype Design of the DC/DC Converter for Fuel Cell Electric Vehicles, Power and Energy Engineering Conference, 2009. APPEEC 2009. Asia-Pacific. /2/ R. Duma, P. Dobra, M. Abrudean, M.Dobra, Rapid Prototyping of Control Systems using Embedded Target for TI C2000 DSP, Mediterranean Conference on Control and Automation, July 27-29, 2007, Athens. /3/ W.S. Gan, Y.K. Chong, W. Gong, W.T. Tan, Rapid Prototyping System for Teaching Real-Time Digital Signal Processing, IEEE transactions on education, vol. 43, no. 1, february 2000. /4/ A. Rubaai, M.J. Castro-Sitiriche, A.R. Ofoli, Design and Implementation of Parallel Fuzzy PID Controller for High-Performance Brushless Motor Drives: An Integrated Environment for Rapid Control Prototyping, IEEE transactions on industry applications, vol.44, no.4, July/August, 2008. /5/ S.H. Seo, S.W. Lee, S.H. Hwang, J.W. Jeon, Development of Platform for Rapid Control Prototyping Technique, SICE-ICASE International Joint Conference, October 18-21, Busan, 2006. /6/ K.H. Hong, W.S. Gan, Y.K. Chong, K.K. Chew, C.M. Lee, T.Y. Koh, An Integrated environment for rapid prototyping of DSP Algorithms using MATLAB and Texas instruments' TMS320C30, Microprocessors and Microsystems 24, 349-363, 2000. /7/ Z. Fang, Y. Qi, Q. Zhang, T. Chai, Design and Implementation of a Low Cost DSP Based Rapid Control Prototyping System, Industrial Electronics and Applications, ICIEA 2009. /8/ Z. Fang, N. Song, L. Wang, Design and Implementation of a Novel Fuzzy Controller with DSP for Rotary Inverted Pendulum, Control and Decision Conference, 2009. /9/ Real-Time Workshop, User's Guide Version 7.4, 2009. /10/ Texas Instruments, Incorporated, Reference Guide, TM-S320x2833x, 2823x Enhanced Quadrature Encoder Pusle (eQEP) Module, SPRUG05A, avgust 2008. /11/ Texas Instrumets, Incorporated, Data Manual, TMS320F28335, TMS320F28334, TMS320F28332, TMS320F28235, TMS320F28234, TMS320F28232, Digital Signal Controllers (DSCs), SPRS439F, junij 2007. /12/ Burr Brown Corporation, ADS1212, ADS1213, 22Bit analog to digital converter, USA, april 1998. /13/ Tan Kok Chye, Teo Chun Sang, Rotary inverted pendulum, Scool of electrical and electronic engineering, 1999. /14/ Zdenko Mezgec, Andrej Medved, Amor Chowdhury, Rajko Svečko,. Mobile payments - design of new terminal = Mobilno plačevanje - razvoj sodobnega terminala. Inf. MIDEM, mar. 2008, letn. 38, št. 1(125), str. 53-60. Nikolaj Semenič1, Andrej Sarjaš2, Rajko Svečko2, Amor Chowdhury1 1Margento R&D, Gosposvetska c. 84, 2000 Maribor 2FERI, Smetanova ul. 17, 2000 Maribor E-pošta: nikolaj.semenic@margento.com Prispelo: 01.07.2010 Sprejeto: 24.06.2011 131 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana AEWSN: ACADEMIC EDUCATIONAL WIRELESS SENSOR NETWORK Karl Benkič, Marko Malajner, Žarko Čučej Fakulteta za elektrotehniko, računalništvo in informatiko Maribor, Maribor, Slovenia Key words: Wireless sensor networks, AeWSN, modeling, simulating, evaluating Abstract: Wireless sensor network (WSN) is a collection of wireless sensor nodes with wireless communication capability which is often used for military application, real-time surveillance, and similar time-critical applications. This article offers an overview of a wireless sensor network system called AeWSN. AeWSN is a custom designed WSN with software and hardware support. The proposed system was developed as a byproduct of PhD studies and is intended for use as an academic wireless sensor research platform, offering some sort of a framework for higher (level 3 or higher) ISO/OSI layer development in WSN. It offers network and protocol modeling, developing, simulating and experimental testing as well as evaluating it. Finally we demonstrate AeWSN on a simple application. AeWSN: akademsko izobraževalno brezžično senzorsko omrežje Kjučne besede: Brezžična senzorska omrežja, AeWSN, modeliranje, simuliranje, ocenjevanje Izvleček: Brezžična senzorska omrežja (BSO) so postala zanimivo raziskovalno področje v preteklih nekaj letih. Zaradi določenih razlik s podobnimi tipi omrežij (Ad-hoc, MANET) raziskave potekajo dejansko na vseh plasteh referenčnega ISO/OSI modela. Za testiranje ali razvoj novih algoritmov za uporabo v brezžičnih senzorskih omrežjih je ključnega pomena, da le te najprej simuliramo v simulacijskem okolju, kasneje pa še ovrednotimo in testiramo na realnem brezžičnem senzorskem omrežju. V ta namen je potrebno najprej izbrati dobro simulacijsko okolje in znotraj le tega razviti ustrezen model brezžičnega vozlišča. Obstaja več simulacijskih orodij za simuliranje brezžičnih senzorskih omrežij (OMNET++, OPNET, GloMoSim,...), vsako od njih pa ponuja določene pozitivne in negativne lastnosti. Kljub razširjenosti simulacijskih orodij v bistvu ne obstaja nobena širša študija, ki bi opredelila uporabnost ali prevlado enega od teh. Med izbiro simulatorja za BSO smo najprej izbrali dva potencialno nam najbolj priročna orodja: OPNET in OMNET++. Izbiri OPNET-a je so botrovale izkušnje, ki jih z orodjem imamo in dejstvo, da OPNET ponuja (sicer zaprti) model senzorskega vozlišča ZigBee tehnologije. Za razvoj svoje lastne platforme smo se odločili predvsem zaradi preprostega spreminjanja strojne opreme po potrebi in zaradi pridobivanja znanja in izkušenj, ki ga to delo prinaša. Razvito senzorsko vozlišče SPaRCMosquito med drugim omogoča tudi zamenjavo strojne programske opreme na daljavo, kar velja za eno najbolj priročnih lastnosti vozlišča. Kljub veliki ponudbi programske opreme pa smo zasledili pomanjkanje take, ki omogoča modeliranje BSO in povezovanje sistemov v celoto. Tako je nastala AeWSN (Academic education wireless sensor network) platforma, ki združuje programsko in strojno opremo ter model simulatorja. AeWSN je sestavljen iz treh glavnih sklopov: Strojne opreme (SPaRCMosquito), programske opreme (SPaRCSoft) in simulacijskega modela (SPaRCSimMod). SPaRCMosquito senzorski modul temelji na Cortex 1768 mikroprocesorju in MRF24J40 radijski enoti. Senzorski modul omogoča zamenjavo strojne programske opreme na daljavo ter uporabo različnih senzorjev združljivih z AD, SPI, CAN in I2C vodilom. SPaRCSoft je skupek programske opreme: strojne programske opreme, ki teče na SPaRCMosquito modulih in SPaRCSoft programa (Fig. 4), na katerem je programska oprema, ki kontrolira SPaRCMosquito bazno postajo (BS). SPaRCSoft omogoča, da se SPaRCMosquito obnaša kot bazna postaja, navadna senzorska enota ali vohljač. SPaRCSoft omogoča modeliranje in realno časovni prikaz stanja omrežja (Fig. 5 in Fig. 6), kjer s pomočjo lokalizacije izrisujemo senzorska vozlišča in v določenem razmerju glede na realno omrežje. Delovanje AeWSN sistema smo preizkusili v par različnih aplikacijah, med drugim tudi na problemu določanja lokacije posameznih senzorskih vozlišč. . 1. Introduction Wireless sensor networks has become intensive research field recent years. Due to their difference from conventional Ad-Hoc wireless networks, researches have covered all the layers of an ISO/OSI model. Originally, IEEE as the Working Group for Wireless Personal Area Networks (WPANs) defined the 802.15 standard, and soon the 802.15.4 standard known as low-rate wireless personal area networks was defined. ZigBee alliance /1/ built their wireless sensor network solution called ZigBee on top of the 802.15.4. standard, as used for physical and medium access layer. Primarily the need for wireless sensor networks arose in army applications. Remote battlefield and Base-Camp surveillance became simpler and possible using wireless technology. In the future, military applications and decisions will be based more and more on data gathering, including data from the battlefields. WSN is one of the most promising intelligence data gathering systems /2/. A typical WSN consists of a large number, even a few thousand, nodes equipped with different types of sensors, microprocessors, radio transceivers, and usually an autonomous power supply, deployed randomly within the area of interest with the goal of collecting sensors measured data and transferring it through one or more data sinks called User Access Point (UAP) or a Base Station (BS) to the end users of WSN services. The random deployment of sensors, for example in battlefields or in plantations, usually means that the positions of the nodes are neither known exactly nor accessible for maintenance and local administration. Consequently, they should have the capabilities for self-organization, within an ad-hoc multihop 132 K. Benkic, M. Malajner, Z. Cucej: AeWSN: Academic educational wireless sensor network Informacije MIDEM 41(2011)2, str. 132-138 network fashion. Under normal working circumstances the majority of traffic flows towards BS /3/, since the BS is a data collector. 1.1. Problem formulation When developing new algorithms, it is crucial to test and evaluate them. Testing and evaluating is possible through two phases: simulating and evaluating the algorithms in the simulators and then testing, and evaluating algorithms on a real WSN. When simulating the WSN, it is crucial to have a good wireless sensor network and node model and, of course a suitable simulation tool. There are several network simulators (NS2, OMNET++, OPNET) to choose from but mainly none of them supports WSN natively. OPNET /4/ supports practically all physical radios with many types of modulations and, therefore, it is quite easy to implement a custom PHY layer for wireless communications. Among other models OPNET supports ZigBee and all three types of devices (RFD, FFD and Coordinator). For PHY and MAC layers there is source code available, but for the network and application layers there is only an object code. OMNET++ on the other hand, offers a good discrete simulator and 3 party models for the WSN simulations /5/ with or without the limited support, what is expected, because the majority of simulation models are open source projects, done by non-profit organizations (faculties) or individuals. The authors in /6/ offered answers which simulator is more appropriate for certain types of simulation (for example: they recommend the NS-2 simulator for high-precision PHY layers simulation) and how a simulator differs in the same setup and scenarios. The same comparison was done in /7/ where the authors found great differences in MANET simulations executed in the OPNET Modeler /4/, NS-2 and GloMoSim. For example: OPNET simulates a very high time delay in MANET compared to NS-2 and GloMoSim /7/. After evaluation the OPNET simulation tool was selected for simulating WSN. When selecting the hardware evaluation platform a decision had to be faced: to use one of the existing platforms for wireless sensor networks or develop a new one, despite a few solutions available on the market. AeWSN is developed for education and research work, which at some point include working with images, so the WSN node should use a CPU which is powerful enough. We didn't want to depend on only one CPU, sensor(s) and radio modules; so, the node has to have modular design. Different setup properties and experiments led us to believe that custom hardware would be the smart choice for us. Hardware choice was based on our previous knowledge, and support from different vendors and companies. The third part of the problem was the appropriate support software selection. Because there is practically no similar software for developing protocols and evaluating WSN parameters it was decided to create one. 1.2. Related work There are a lot of manufactures who provide the market with solutions for wireless sensor networks. Some manufactures created a consortium called ZigBee Alliance /1/. Zigbee alliance proposed high layer communication protocol based on IEEE 802.15.4 standard for wireless personal networks (WPAN). The main advantage of a ZigBee is its simpler and cheaper protocol in comparison with Bluetooth, which makes ZigBee very appropriate for wireless sensor networks. Two alliance members, Microchip and Texas Instruments are the world's best-known providers for ZigBee protocols and equipment. As a member of the ZigBee Alliance, Microchip offers its customers a certified ZigBee Compliant Platform (ZCP) for the ZigBee® PRO, ZigBee RF4CE, and ZigBee 2006 protocol stacks. The ZCPs ensure interoperability with the ZigBee industry standard. Microchip's ZigBee Compliant Platforms consist of the 2.4 GHz IEEE 802.15.4 compliant MRF24J40 transceiver products, the PIC18, PIC24, dsPIC, and PIC32 families of microcontrollers, and the certified firmware protocol stacks. TI offers cost effective low power RF solutions for the ISM band, ZigBee hardware and software solutions. TI's product offers include RF transceivers, RF transmitters, RF receivers, System-on-Chips, Front Ends and ZigBee Processors. Some universities and companies use basic hardware to produce their own wireless sensor nodes but, in general, almost all of them use IEEE 802.15.4 compliant hardware. Table 1. shows the that market offers WSN nodes ranging from simple low power CPUs to high performance ARM processors (PXA271). A conclusion can be made that the selection of a WSN node is typically depended on application. Table 1: The comparison of some WSN nodes available on the market. WeC Mote Mica2 Mote MiCAz Medusa MK2 ^AMPS Imote2.NET Radio TR1000 CC1000 CC2420 TR1000 LXM3162 CC2420 MCU AT90LS8535 ATMEGA128L ATMEGA128L ATMEGA 128L AT91FR4081 ARM StrongARM SA-1100 Marvell PXA271 Operating system Tiny OS TinyOS uCos-II eCos Win CE, .NET micro framework Memory 23KB EEPROM 128 + 512K FLASH 128 + 512K FLASH 1MB FLASH 32MB FLASH 32MB SDRAM 133 Informacije MIDEM 41(2011)2, str. 132-138 K. Benkic, M. Malajner, Z. Cucej: AeWSN: Academic educational wireless sensor network 2. AeWSN.NET system 2.1. Hardware - SPaRCMosquito The Laboratory for Signal Processing and Remote Control (SPaRC) has developed its own wireless sensor node platform called SPaRCMosquito. One of the reasons for developing its own platform was the absence of an ARM microcontroller based sensor node platform on the market. Microcontrollers based on ARM architecture are very popular these days for mobile devices due to their small power consumption, efficiency, reasonable prices, etc. Two sensor node platforms have been developed. One for connecting to a PC, used for data gathering (base station), which is named the SPaRCMosquito Base Station. The independent sensor node, deployed for the field (sensor node), is called SPaRCMosquito. Microchip's MRF24J40 radio module /8/ based on 802.15.4 standard and Tl's CC2500 radio module /9/ were chosen for the wireless part. 2.1.1. SPaRCMosquito Base Station The task of a base station is the gathering of data from an entire wireless sensor network, so, the connection to the higher entity is needed. The SPaRCMosquito Base Station can communicate with a PC, laptop, etc. via USB link. The hearth of base station is a low power LPC 1768 Cortex, 32-bit microcontroller. In addition to the microcontroller, the platform consist of USB and LED drivers, JTAG connector, general-purpose connector (includes I2C, SPI, ADC and GPIO) and other. The power supply is assured over the USB connection. Fig. 1 presents the SPaRCMosquito Base Station. Fig. 1: SPaRCMosquito base station 2.1.2. SPaRCMosquito Sensor Node The SPaRCMosquito Sensor Node is based on the same platform as the base station with some modifications. There is no longer USB driver and some LED indicators. Instead a connector for the sensor (for measuring physical phenomena), a DC/DC converter and flash memory have been added (Fig. 2). MRF24J40 Daughter board The MRF24J40 Daughter board from Microchip is a wireless radio originally designed for the PICDEM Z evaluation platform. This module was used for the SPaRCMosquito platforms. MRF24J40 is fully compatible with IEEE802.15.4 (ZigBee and MiWi). Communication between radio module and microcontroller is established over a 4-wire SPI protocol. CSMA-CA, automatic acknowledge and retransmit are implemented physically on a chip. The data rate is up to 250 kb/s with QPSK modulation and center frequency 2,4 GHz. CC2500 Radio Module The CC2500 is a low-power, low cost radio transmitter from Texas Instruments. CC2500 is very appropriate for wireless device like PC mouse, etc. Its embedded modem is designed for a few different modulations: MSK, 2-FSK, GFSK, OOK) and programmable data rates up to 500 kb/s. Power consumption in the receiving mode is 13,3 mA. The surrounding temperature can be measured using a build-in analog temperature sensor. In order to implement the CC2500 radio module only a chip was purchased, because only a chip, few extern passive elements and folded cupper dipole antenna on substrate is needed for the assembly /10/. Fig. 2: SPaRCMosquito sensor node 2.2. Software - SPaRCSoft As mentioned in section 1, wireless sensor networks use at least one base station. A base station is computationally more powerful, with more available resources than standard sensor nodes. In the case of using centralized algorithms (e.g. topology, routing, addressing), the base station normally calculates them. The base station is not normally battery powered, so the energy consumption limitations for the BS do not stand. In a typical sensor network application, the sensor nodes deployed in the field have low CPU power, limited resources and most importantly: limited power supply. The majority of algorithms (MAC, topology, routing) for WSN are designed for preserving battery power. 134 K. Benkic, M. Malajner, Z. Cucej: AeWSN: Academic educational wireless sensor network Informacije MIDEM 41(2011)2, str. 132-138 Fig. 3: Data frames used in AeWSN.NET Frame 00001 Time(us) +1816512 =1816512 Len 15 MAC Frame Control 0x8841 Seq Mum 0x05 Cest PA M 0x1234 De st Addr 0x0005 Source Addr 0x1111 Invalid Data 0x25 0x25 0x25 0x25 FC S RSSI Corr CRC OxEB 0x69 1 Software covering the AeWSN.NET can be divided into three main parts: - Software for the SPaRCMosquito (also referred as node firmware). - Base station software, including BS firmware and communication protocol to the PC. - SPaRCSoft, base station and utility software. SPaRCSoft and all other program components are still the subject of on-going research. Because of this, new modules and algorithms are added weekly. Wireless communication in AeWSN.NET is based on IEEE 802.15.4. standard /11/. All sensor nodes (including base stations) are using the MRF24J40 module for communication. MRF24J40 is a ZigBee compliant transceiver but, in our case, only data frames with short addressing fields are used (Fig. 3) /11/. For developing localization, topology, and routing algorithms, the ZigBee or the MiWi stack is too large and complex; therefore we implemented our own, simple algorithms. 2.2.1. SPaRCMosquito firmware The SPaRCMosquito is, as mentioned in section 2.1.2, based on Cortex 1768 CPU (ARM7 architecture). The programming of a processor is done in ANSI C language with the use of KEIL development tools. The main parts of the software are drivers: for communication with the radio MRF24J40, sensor part drivers, boot loader (a custom boot loader is used for flashing purposes as explained below), and the main application, including topology controls, and routing. When deployed, the sensor node becomes part of the wireless network. Testing, routing, and topology algorithms on already-deployed networks can be difficult if the firmware can't be replaced remotely. It is for this reason that why we are developing sensor node(s) which can be reprogrammed online (upgraded with any new version of the firmware). If we want to upload new firmware on the sensor node, we must reprogram the microcontroller's flash memory with new firmware. The Internal LPC's flash memory 512KB with external 1MB memory flash has been extended for this purpose. We have developed an "extended" bootloader which flashes the ARM from firmware on the external memory flash. New firmware is transferred from base station to each sensor node wirelessly. Each sensor's node stores new firmware in external flash memory. When done, the first byte flashed on the external flash is marked as 0x01 (new firmware). The program running on the ARM resets the ARM. When entering our own bootloader, first, the check of the first byte on the external flash is made. If the first byte is set to 0x00 the ARM boots normally, otherwise (if the first byte on the external flash is set to 0x01), code in our bootloader copies firmware from the external flash to ARM internal flash, clears the first byte on the external flash, and moves the program counter to the start of the program just flashed. 2.2.2. SPaRCSoft SPaRCSoft is the main application in the AeWSN.NET system. WSN modeling, testing, and evaluating is done using this application. It is also a gateway to the WSN base station. SPaRCSoft runs on a PC and can be connected to a WSN base station via USB /12/, /13/. The software is modularly based, and currently consist of eight modules (Fig. 4) working together. The I/O module is the SPaRCMosquito interface. Currently SPaRCMosquito is connected as a virtual com port (VCP) to the PC. The I/O module frames the data from the application module and sends it towards the base station or receives the data, creates an identical data structure, as seen in Fig. 4 and then forwards it to the application module. Application module contains the firmware for the base station. Due to firmware, the BS hardware module can act as a base station, regular module, analyzer module (like Microchips Zena), and a sniffer. All higher modules communicate with the application module. Remote firmware upgrade module reads the binary file using the nodes firmware and distributes it over the network as stated in section 2.2.1. Web server module is used for accessing data over the internet (e.g. reading temperature or moisture). WSN properties module uses evaluation metrics for evaluating protocols if necessary. SPaRCGraph module calculates different topology and routing algorithms and distributes the virtual topology over the network. Data for simulating are available through this module. Meta data module prepares data and information for simulating in OPNET or for firmware development. Internal settings for the modules are, if necessary, all read from the XML. Users can change it to XML or in SPaRCSoft GUI, if offered. Some settings (like com port settings) can only be changed only in XML. 135 Informacije MIDEM 41(2011)2, str. 132-138 K. Benkic, M. Malajner, Z. Cucej: AeWSN: Academic educational wireless sensor network The basic structure of the SPaRCSoft is a mathematically defined undirected graph G = (V, E, W) with vertexes (sensor nodes), edges (communication links between them), and weights (function of channel properties, delay and similar). The graph model is used for all the protocol calculations. SPaRCSoft can work online (connected to the real network) or offline (as a modeling and analyzing tool). When working online, sensors can be visualized as a graph on the SPaRCSoft graphic panel. Nodes are randomly distributed and the link shows the nodes neighbors. Of course, the graph can be imported (for example TSPLIB), created by the user or created randomly (working offline). When the basic structure is created (or imported) calculations can be done on it. The majority of the research work is done according to topology and routing protocols, so the SPaRCSoft is prepared for the mentioned topics. From the ISO/OSI perspective the physical and data link layers are implemented on the MRF modem (PHY and MAC). Higher layers (topology, routing) are implemented in the application module. Fig. 4: SPaRCSoft modules Let's assume that 10 wireless nodes and the base station are in WSN at the moment and the initial phase of creating the network is over. The network topology is shown in Fig. 5. All nodes are transmitting at 100% of their power. The circle around node 10 represents its communication radius without channel properties - the gray color. The communication radius with logarithmic channel model is displayed in the green color. We decided that simple topology routing (minimum spanning tree - MST) would be used. SPaRCSoft firstly calculates MST, after that the software calculates the communication radius reduction for every node that still guarantees the MST topology (Fig. 6). Information about the topology and routing is flushed over the network and the network can be turned into a running mode. It can be seen that node 2 energy was reduced by 50%, and if the free space propagation model is used /14/ Eq.1, energy saving can be simply calculated. P P =C — ^ W r2 (Eq. 1. Where Pr = received power, Cf = transceiver characteristics, Pt = received power, r = distance. Fig. 5: WSN topology Fig. 6: Calculated "virtual" topology Topology control is practically done using changing transmission power. If all the MRF module features were be used, the channel number could be used for topology control (in the sense of creating links with different channel numbers). The SPaRCGraph module, in the case of topology control calculates transmitting power of every node that still enables desirable topology (e.g. Connected, MST, RNG, minR) /14/. Energy consumption, from the topology point of view, mainly depends on the transmitting power. Some examples showed us that two hops are less energy-demanding that only one /14/, but achieving a minimum number of hops within a network can sometimes be one of WSN properties goals. This is why we are convinced 136 K. Benkic, M. Malajner, Z. Cucej: AeWSN: Academic educational wireless sensor network Informacije MIDEM 41(2011)2, str. 132-138 that topology control is an important factor in developing WSN routing. 3. Application example - Localization All data from the sensor's field are usually collected on the base station and this data is usually meaningless without positional information. Therefore, the node's location or position estimation has been a very interesting research topic over the last few years. Position estimation facilitates applications, such as inventory tracking, intruder detection, tracking of fire-fighters or miners, home automation, and patient monitoring. There are many techniques for determining the distances between nodes. Physically, we can measure the time of a signal (acoustic or RF) arrival, the angle of the signal arrival or power of the received signal. Our research focused on measuring the strength of the received signal (RSSI - Received Signal Strength Indicator). The RSSI technique was chosen due to its integration in most 802.11 radio modules. RSSI practically allows us to calculate the received power for each received packet. This parameter can be used together with path-loss and shadowing model for distance estimation. A centralized algorithm is used for calculating the coordinates of the sensor's nodes. The base station sends RSSI parameters from the entire sensors field (all the nodes) to the PC. Then the PC calculates all the coordinates of the sensors within the network. The packets consist of next data: addresses from two neighboring nodes and RSSI between them. The algorithm calculates the average value of the last 20 measured RSSI and calculates the distances between nodes using one of the appropriate path-loss models (Fig. 7). The first three calculated distances be- tween the nodes creates three reference nodes (anchors or beacons). When we have reference nodes it is easy to calculate other node's coordinates. 3.1. Localization error During the experiments we discovered that the relative localization error could reach up to 30%. In a typical radio link transmission, waves are reflected and obstructed by all objects illuminated by the transmitter antenna. Calculating the distance within realistic environment is a very complex task. Relative errors occur because of this. Fig. 8 shows relative errors from three different scenarios calculated from ideal models and real measured values /15/. 25 15 10 0 50 100 150 200 250 300 Distance [cm] Fig. 8: Localization error 4. Conclusion In this article, an overview of a wireless sensor network platform called AeWSN is done. Nowadays wireless sensor networking is a very promising, rapidly growing research field. Therefore, many vendors offer wireless transceivers (based on IEEE 802.15.4) or complete wireless sensor nodes (MicaMote, ¡MOTE2...). Despite this, we decide to develop our own wireless sensor node for the AeWSN platform. Developing our own platform gives us the freedom to simply modify the hardware and/or the software to our needs for research or project work, not to mention the experience and knowledge gained during the hardware and software development. AeWSN is still a subject to an ongoing research and development project. Our main goal is to fulfill an AeWNS platform with OPNET simulator node model, which would have the same characteristics as SPaRCMosquito. When the project is stable enough we are planning to launch a web site and making AeWSN a public open-source platform. Finally a simple localization application example is demonstrated as a case study, as to how AeWSN platform works. Fig. 7: SPaRCSoft module 137 Informacije MIDEM 41(2011)2, str. 132-138 K. Benkič, M. Malajner, Ž. Čučej: AeWSN: Academic educational wireless sensor network Bibliography /1/ Z. Alliance. (2010, Mar.) ZigBee Alliance. /Online/. http://www. zigbee.org/ /2/ B. Ames, »Electronics are central to 21st century warfare tactics,« military and Aerospace Electronics, 2004. /3/ H. Dai and R. Han, »A node-centric load balancing algorithm for wireless sensor networks,« in Global Telecommunications Conference, 2003. /4/ OPNET. (2010, Mar.) OPNET. /Online/. http://www.opnet.com/ /5/ OMNET++. (2010) Simulation Models. /Online/. http://www. omnetpp.org/models /6/ L. Hogie, P. Bouvry, and F. Guinand, "An Overview of MANETs Simulation," Electronic Notes in Theoretical Computer Science, 2006. /7/ D. Cavin, Y. Sasson, and A. Schiper, "On the accuracy of manet simulators," Proceedings of the second ACM international workshop on Principles of mobile computing, pp. 38-43, 2002. /8/ Microchip. (2009) MRF24J40. /Online/. http://www.microchip. com/wwwproducts/Devices.aspx?dDocName=en027752 /9/ T. Instruments. (2009) Low Power RF ICs - 2.4GHz - CC2500 -TI.com. /Online/. http://focus.ti.com/docs/prod/folders/print/ cc2500.html /10/ M. Malajner, K. Benkič, and Ž. Čučej, "Implementacija sprejemno/oddajnega modula CC2500 za uporabo v brezžičnih senzorskih omrežjih," in Zbornik šestnajste mednarodne Elektrotehniške in računalniške konference ERK 2007, vol. A, Portorož, 2007, pp. 140-143. /11/ D. Gislason, ZigBee Wireless networking. Elsevier, 2008. /12/ K. Benkic, M. Malajner, A. Peulic, and Z. Cucej, "Academic education Wireless Sensor Network: AeWSN," in Proceedings ELMAR, Zadar, 2008, pp. 535-538. /13/ K. Benkic, M. Malajner, and Z. Cucej, "AeWSN.NET: framework for the wireless sensor networks," in New Master curricula and EU practice : proceedings, Niš, 2008, pp. 91-94. /14/ P. Santi, Topology control in Wireless Ad Hoc and Sensor Networks. John Wiley & Sons, Ltd, 2005. /15/ M. Malajner, K. Benkič, P. Planinšič, and Ž. Čučej, "The accuracy of propagation models for distance measurement between WSN nodes," in In Proceedings of 16th International Conference on System, Signals & Image Processing, vol. 3, Chalkida, Greece, 2009. mag. Karl Benkič, mag. Marko Malajner, prof.dr. Žarko Čučej Fakulteta za elektrotehniko, računalništvo in informatiko Maribor, Smetanova 17, 2000 Maribor Prispelo: 29.03.2010 Sprejeto: 24.06.2011 138 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana THZ IMAGING SYSTEM FOR HIDDEN OBJECTS DETECTIONS Andrej Svigelj, Janez Trontelj University of Ljubljana, Faculty of electrical Engineering, Ljubljana, Slovenia Key words: THz sensor array, bolometer, THz imaging, Hidden objects detection Abstract: The motivation of the work is to develop a flexible and low cost THz imaging system which can be used for various security applications. The key element is therefore a room temperature operation of THz sensor element capable to be integrated into a sensor array. The selected sensor is antenna-bolometer type which can be fabricated with micro-system and micromachining technologies based on silicon wafer substrate allowing low-cost mass production. These fabrication technologies are available in Laboratory for Microelectronic at Faculty of Electrical Engineering. Additional electronic and signal processing is described in the paper providing THz image. The complete system is described and results of THz images are presented. THZ vizijski sistem za odkrivanje skritih predmetov Kjučne besede: Polje THz senzorjev, bolometer, THz vizijski sistem, detekcija skritih predmetov Izvleček: Cilj dela je razvoj prilagodljivega in cenovno ugodnega THz vizijskega sistema ki se lahko uporablja v številnih aplikacijah, predvsem pa v varnostne namene. Ključni element sistema je delovanje THz senzorskega elementa pri sobni temperaturi in možnost integracije elementa v polje THz senzorjev. Izbrani senzor je tipa antena-bolometer, ki je lahko izdelan s tehnologijo mikrosistemov na osnovi silicija, ki omogoča nizkocenovno masovno proizvodnjo. Takšna tehnologija je na voljo tudi v Laboratoriju za mikroelektroniko na Fakulteti za elektrotehniko. V prispevku je opisan celoten sistem, skupaj z dodatno elektroniko in procesiranjem signalov, ki omogoča izdelavo THz slike. Na koncu so prikazani tudi rezultati slik dobljenih z opisanim sistemom. 1. Introduction One of the most important benefits of the THz radiation is that its photons have low energies and do not cause harmful photo-ionization in biological matter. The mm Waves are also known for good penetration through different materials, like clothes, paper, plastic, ceramic. /1/ Different materials can also be identified by their specific spectral response in THz region. This makes mm waves very useful in many applications such as industrial process inspection, pharmaceutical product inspection, radar applications, high speed communications, biomedical imaging and security purposes like explosive detection and THz imaging instead of X-ray imagers. A THz low cost imaging system for hidden objects detection which is capable of detecting a hidden object through multiple layers of different types of clothes is presented. It is capable of producing the image of size up to 32x32 pixels. The image is processed and observed on laptop computer with near real time image refresh rate. 2. THz imaging system design The concept of a THz vision system is based on the reflected pattern of THz waves from the target. In figurel the complete system is shown. It consists of a THz continuous wave source emitting at 0,3THz with an output power nominally 1mW. The reflected waves from the target are gathered with a Fresnel type lens with diameter of 250mm. The detector pixel array of 16 detectors positioned in a horizontal line is processed in parallel, while the vertical scanning is processed sequentially to cover the array of 16 x 16. The goal is to obtain a full 256 pixel array. The physical size of the detector array is therefore 27 mm x 27 mm. The signals from the array are processed with a laptop using National instruments USB-6251 Mass Term 16-Bit, 1.25 MS/s M Series Multifunction DAQ and Lab View based software. ïftir« •'.y'1-. Fig. 1: THz imaging system 2.1. Pixel design For the THz pixel a bolometer operating at room temperature has been chosen. In the literature the best NEP figures for a bolometer are in the range of hundred of pW^Hz. As our target is in 1.5m - 3m away from the THz source and detector, such figures are not acceptable. A novel antenna and bolometer THz pixel has been developed with a NEP value in the range of 20 - 30 pW^fe. /3/ Such figure is actually extending state of the art for room temperature THz sensors. The bolometer is fabricated on a silicone-dioxide foil with a thickness of 2 pm, the bolometer element is lifted above it with the dimensions of 10um x 1um. The sensitivity figure for such element is close to 100V/W, the bolometer resistance is 300Q. It has been proved that the noise voltage corresponds to Johnson noise of 300Q resistor. The bias current of the bolometer is 1mA which increases the operating temperature for about 30 139 Informacije MIDEM 41(2011)2, str. 139-143 A. Švigelj, J. Trontelj: THZ Imaging System For Hidden Objects Detections degrees above the ambient temperature. Fig.2 shows the antenna bolometer photog Fig. 2: Photomicrograph of antenna-bolometer 2.2. 4x1 pixel array An array of 4 x 1 pixel array has been designed and fabricated to provide a building block for larger array. The antenna dimensions are roughly 1mm x 1mm, providing effective area of 1mm2. The 4X1 pixel array was fabricated in LMFE using its micro system and micromachining facilities. The pitch was selected to be 1,7mm to allow an easy way to join the 4x1 to a larger pixel matrix. Figure 3 shows a test PCB containing the 4x1 pixel array. Fig. 3: 4x1 pixel array 2.3. 16x1 pixel array A Linear array of 16 pixels, assembled with four parts of 4 X 1 arrays, together with connection wires and capacitors for ESD protection is shown on Figure 4. To minimize the number of electrical joints, the contacts from bolometers are bonded directly to PCB board which has to be gold-plated to allow gold wire ball bonding. Figure 5 shows a photo of the final 16 pixel array together with the associated bolometer biasing and amplifying electronics. Fig. 5: linear array of 16 pixels with pixel electronic 2.4. Amplifier The most critical element is LNA (Low noise amplifier) /2/ which should generate lower noise compared to bolometer nose. The measured noise of the amplifier is close to 5nV^fe at 300 Hz which is the chopping frequency of the THz source. The amplifier is AC coupled with the gain transfer bandwidth characteristic shown in figure 7. The LNA Is connected in a close loop configuration with high pass filter to avoid the LNA offset amplification and a low pass filter to suppress high frequency noise. In figure 6 the schematics of complete electronics for one pixel is shown. 5V 330pF GND i r -AAV > I -5V Fig. 6: Complete pixel electronic schematic Fig. 4: Linear array of 16 pixels 140 A. Svigelj, J. Trontelj: THZ Imaging System For Hidden Objects Detections Informacije MIDEM 41(2011)2, str. 139-143 Fig. 7: Gain transfer bandwidth characteristics of amplifier Fig. 11: FFT of signal with poor reflection 2.5. Signal Processing Figure 8 shows a typical signal obtained on the pixel in the case that there is a fair reflected signal. If there is no reflected signal there is almost no 300Hz signal as shown on Figure 9. As seen the signal to noise ratio would need to be improved. This was done by using Fast Fourier Transform (FFT) which gave quite good result as shown in figure 10 and 11. 0; | Um- ï. 16m- ■Ilm- Km: 6 o y.ixjj u.tu OOjj t—N 0.0J V.Ott U,IH (J.W! M Fig. 8: Pixel signal with good reflection Fig. 9: Pixel signal with poor THz reflection 2.200m 7,000m-j^M I .«Cm j^V: 1.600m 1 m 1 * ' um 1 MOOmH^Hj t 3.000m -^^Kr ttC.L.T-j 1 1 JOO.OOOU-I^El 7 S W i25 150 IB JW Ö à ¿5 M ]25 3» 2.6. Mechanical scanner To get a square matrix of 16 x 16 pixels an electro-mechanical micromanipulator is used to move the pixel array of 16 x 1 in vertical direction in 16 steps. To get a symmetrical image, the vertical step must be 1.7mm, which is the same as pixel array pitch. The scanning rate is adjustable by controlling software. The fastest scan rate is 4 seconds for full screen which gives us near real time acquisition of the THz scene. For good signal to noise ratio a longer acquisition time is recommended. It has been introduced an increase of a pixel array to a size of 32 x 32 with additional electro-mechanical micromanipulator which moves the 16 x 1 array of sensors in horizontal direction for a half of a pixel pitch and scanning in a vertical direction has to be done twice with 32 steps of half of pitch of the pixels 2.7. Image processing In the described project some effort was invested into the image processing algorithms also. Each pixel is represented as a square in the image. For each square a 300 Hz component from the FFT of the measured signal is represented with 256 shades of grey. Because the difference in signal levels can be very high, compared to 256 levels, two algorithms were implemented. At first all values can be normalized in the way, that the highest value is 255. To present a larger value Fig. 10: FFT of reflected signal Fig. 12: Optical photo of the target 141 Informacije MIDEM 41(2011)2, str. 139-143 A. Svigelj, J. Trontelj: THZ Imaging System For Hidden Objects Detections span, all values can also be exponentiated which provides the same effect as gamma correction in standard video signals 3. Results The raw image suffers from well known resolution limitation which is governed by the ratio of lens diameter and THz wavelength. In our case the expected resolution was no better than 1mm. An optical photo of the target is shown on figure 12 and its THz image on the figure13. For this image the pixel count was increased to 32 x 32 and only a resolution enhancement was implemented. i 1 _ J _ 1 1 ; _ ■ 1 fl ■ 1 _ ■ s Fig. 13: THz image of the targed Two layers of clothes are covered over the target as shown on figure 14 and its THz image is shown on figure 15. An additional two layers of T-shirt and a towell are covered over the previous two layers of clothes as seen on figure 16. The THz radiation can penetrate through all these layers, as it can be seen from the figure 17. Fig. 14: Optical photo of covered target 142 I I I II II II II J I rrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrr R iff "i M rrr rrrn rrrrrrrrrrrrrrrrrrr PtT^ ibtt^Mrrui rrri rrrrrl rrrrrl rrrrrl rBTrrrrnrrr^l ' :. ; ' Kiriti _ r s ■■■ - r ' Pi H ppirNLUT i i ■■ | I i h h i i i r OSflKi:'in rrr[-rr ttKB^tP!'"Ft .Li rrrrr fflMEU ■ rrjpjjiifr FrFFFrrrrrrrFrFnSî r h T i r ;rr I ] i r rr r r c rrrrrrrrrrrrrrrrrrr n rrrrrrrrrrrrrrÉrr rrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrr ^rrrrr "rrrrr "rrrrr rrri irrn -rm n^rn rrrrr r, rrr "rrrrr "rrrrr "rrrrr TFrr "rrrrr "rrrrr "rrrrr _rrrrr rrrrr irrrri Tr rr "rrrpf" "rrrrr "rrrrr "rrrrr rrrrrr r rrrrr rrrrrr rrrrrr rrrrrr rrrrrr rrrrr rr—rr rrrrr rrrrr rrrrr rrrrr rrrrr Fig. 15: THz image of covered target Fig. 16: Optical photo of multiple layer covered target Fig. 17: THz image of multiple layer covered target A. Švigelj, J. Trontelj: THZ Imaging System For Hidden Objects Detections Informacije MIDEM 41(2011)2, str. 139-143 4. Conclusions A low cost THz antenna-bolometer type imaging sensor array of 1x4 and 1x16 has been designed, fabricated and demonstrated at room temperature conditions. A system for near real time imaging has been introduced with capability of producing the image of up to 32x32 pixels. Additional signal processing has been performed on laptop computer and the detection of the target under multiple layers of different clothes has been achieved. 5. Acknowledgements This work has been financed and supervised by Slovenian Ministry of Defense under contract number: RR-07-013 6. References /1/ ULRICH R. Pfeiffer, Erik Ojefors. Terahertz Imaging with CMOS/ BiCMOS Process Technologies. Proceedings of the 36th European Solid-State Circuits Conference 14-16 Sep. 2010,Seville, Spain, pp. 52-60 /2/ TRONTELJ, Janez, SEŠEK, Aleksander. Ultra low noise PAGC amplifier for microsystem sensor signal processing. Inf. MIDEM, vol. 35, no. 1, pp. 8-12, 2005 /3/ Dr. Leon Pavlovič, Dr. Drago Kostevc, Dr. Anton Pleteršek, Dr. Marijan Maček, Dr. Aleksander Sešek, Dr. Janez Trontelj.300 GHz Microbolometer Parallel-Dipole Antenna for focal-Plane-Array Imaging, NATO RTO MP SET159 Andrej Švigelj, univ. dipl. ing. el. Univerza v Ljubljani, Fakulteta za elektrotehniko Tržaška 25, SI-1000 Ljubljana E-mail: andrej.svigelj@fe.uni-lj.si Tel: (01) 4768 - 340 Prof. Dr. Janez Trontelj Univerza v Ljubljani, Fakulteta za elektrotehniko Tržaška 25, SI-1000 Ljubljana E-mail: janez.trontelj1@guest.arnes.si Tel: (01) 4768 - 333 Prispelo: 20.10.2010 Sprejeto: 24.06.2011 143 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana CONVERGENCE OF FIXED AND MOBILE NETWORKS BY RADIO OVER FIBRE TECHNOLOGY Boštjan Batagelj, Leon Pavlovič, Luka Naglič and Sašo Tomažič University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia Key words: Radio over Fibre, remote antenna unit, cellular architecture, fibre access, fixed and mobile convergence Abstract: This article presents a solution for the convergence of mobile and fixed access networks on the physical level that allows different service providers to share the same mobile infrastructure. A mobile cell solution is presented which features a fibre optic access infrastructure that is independent of the standard and allows the transmission of different types of broadband telecommunication traffic. For an efficient broadband network frequencies in the millimetre-wave range need to be used (30 - 300 GHz) and the cell size needs to be reduced to a pico (100 m) or even femto (10 m) of a cell. The network presented is based on the transmission of a radio signal over optic fibre, namely 'Radio over Fibre' (RoF). The goal is to transfer complex signal processing functions from the base station to the central station. This decreases the costs of remote antenna units in the base station, making a larger number of picocells a viable solution. Uneconomical radiofrequency signal processing functions such as (de)modulation, synchronisation, multiplexing, frequency hopping, spread spectrum technology and other technologies are now located in the central station. The RF signal created in the central station is distributed through remote base station antenna units which cover the picocells used by mobile users. This article also presents the key building blocks of the RoF system, such as a photodiode with an integrated antenna, an electro absorption modulator, an optic millimetre-wave generator with a phase-locked loop and an optic-controllable antenna. Zlivanje mobilnih in fiksnih omrežij s tehnologijo prenosa radijskega signala preko optičnega vlakna Kjučne besede: prenos radiofrekvenčnega signala prek optičnega vlakna, oddaljena antenska enota, celična arhitektura, vlakenski dostop, fiksno in mobilno zlivanje Izvleček: V članku je predstavljena rešitev za zlitje mobilnih in fiksnih dostopovnih omrežij na fizičnem nivoju, kar omogoča različnim ponudnikom storitev souporabo iste prenosne infrastrukture. Predstavljena je mobilno-celična rešitev z optično vlakensko dostopovno infrastrukturo, ki je neodvisna od standarda in omogoča prenos raznovrstnega širokopasovnega telekomunikacijskega prometa. Za učinkovito širokopasovno omrežje je potrebno uporabiti frekvence v milimeterskem valovnem področju (30 - 300 GHz) in zmanjšati velikost celice na piko (100 m) ali celo femto (10 m) celice. Osnova predstavljenega omrežja je prenos radijskega signala preko optičnega vlakna (angl. Radio over Fiber - RoF), katerega cilj je premestitev kompliciranih funkcij za obdelavo signalov iz bazne postaje na centralizirano postajo. S tem se zmanjšajo stroški oddaljene antenske enote v bazni postaji, tako da je večje število pikocelic smotrna rešitev. Potratne radiofrekvenčne signalno procesne funkcije, kot so (de)modulacija, sinhronizacija, razvrščanje, frekvenčno skakanje, tehnike razširjenega spektra in ostale morebitne so izvedene v centralni postaji. V centralni postaji pripravljen RF signal je razdeljen med oddaljenimi antenskimi enotami baznih postaj, ki pokrivajo pikocelice, kjer se nahajajo mobilni uporabniki. V članku so predstavljeni tudi ključni gradniki RoF sistema, kot so fotodioda z integrirano anteno, elektroabsorpcijski modulator, optični generator milimeterskih valov s fazno sklenjeno zanko in optično vodljiva antena. 1. Introduction The main representatives of today's and future /1/ wireless radio communications are mobile communications and nomadic communications where the user is somewhat less mobile. There are also fixed directional radio connections and fixed one-to-multiple point radio connections, however fibre connections are the most suitable for the stationary user. This renders fixed radio connections obsolete except in cases where optic fibre lines have not yet been laid, or where telecommunication network redundancy needs to be ensured. A fibre optic link is superior to a radio connection in both parameters of significance which determine the value of telecommunication lines /2/. The first is the range of the telecommunication line measured in units of length, where optic fibre is the absolute winner with the attenuation of 0.2 dB/km. The second parameter is link capacity which measures the amount of information transmitted in units of time, where the optic fibre's broadband properties make it a practically bandwidth unlimited medium. Fixed-mobile convergence is a phenomenon which involve services, applications, devices and networks. Meanwhile the service and application convergence have started already /3/, device and network convergence are still on hold since fixed and mobile industry are not ready to merge and to build an integrated radio-optical platform for efficient end-to-end service delivery with guaranteed performance. Although network convergence seems far away from nowadays techno-economical reality, this paper presents technical solutions for the convergence of mobile and fixed access network. Since the end user want to have wireless broadband access, the access network is main convergence point of interest. Today, most base stations are connected to central stations via fibre optics, using the Plesiochronous Digital Hierarchy (PDH), Asynchronous Transfer Mode (ATM) or IP transfer systems. The base station is where conversion 144 B. Batagelj, L. Pavlovic, L. Naglic, S. Tomazic: Convergence of Fixed and Mobile Networks by Radio over Informacije MIDEM 41(2011)2, str. 144-149 to radio frequency occurs, bringing a broadband signal to the user's mobile station, as illustrated in Figure 1. Across greater distances, transmission from the central station to the base stations is achieved via fibre optics. Across smaller distances within the cell area transmission from the base station equipped with an antenna unit to the user is achieved wirelessly using radio waves. Fig. 1: Network segmentation by picocells. For short-range communications, the frequency range of around 60 GHz has been identified, which is the absorption peak of oxygen molecules. Since atmospheric attenuation for millimetre waves is high, radio propagation is limited to small area. For an efficient broadband network frequencies in the millimetre-wave range need to be used (30-300 GHz) and the cell size needs to be reduced to a pico (100 m) or even femto (10 m) radius of a cell. In the new radio frequency plan prepared by Electronic Communications Committee (ECC) within the European Conference of Postal and Telecommunications Administrations (CEPT) /4/, it is clearly evident that frequency bands from 57 GHz to 66 GHz are used for broadband data transmission. The 62 GHz to 63 GHz band is reserved for land mobile broadband connections. The 60 GHz band is highly suitable for use in home communication /5/ where we can already see the first examples of its commercial use. 2. Radio over Fibre The basic idea of technology which allows the transmission of a radio frequency (RF) signal over fibre (Radio over Fibre - RoF) is a simple combination of fixed fibre and mobile RF transmission. The transmission of an RF signal over fibre using optical media /6/ is viable where the network is accessible to the end-user wirelessly using the cellular network. The common principle, which has been in use for a number of years and can be seen in most currently available commercial cellular networks, is illustrated in Figure 2. Optical fibre is used as an effective substitute for a twisted pair or coaxial cable. Through an optical line, comprising an emitting laser diode (LD) and photodiode (PD) transmission is achieved with PDH or ATM, which in recent times are being replaced by IP. With this type of solution the transition from wired to wireless transmission requires a complex signal conversion at each base station. Frequency mixers and a reference RF oscillator are used to up-convert the baseband signal into the modulated carrier needed for the wireless transmission. This network architecture is complex and uneconomical due to its large number of cells. Fig. 2: Transmission over fibre in the baseband and signal processing at the base station. A fibre optical line with a large bandwidth allows the transmission of data signals directly over the RF carrier. In this way complex signal conversions at the base station side can be avoided. The complex signal processing functions are transferred from base stations to the central station. Thus, radiofrequency signal processing functions such as (de)modulation, synchronisation, multiplexing, frequency hopping, spread spectrum technology etc are now carried out at the central control station. The transmission of broadband signal above described is illustrated in Figure 3. In a practical network with a large number of terminal base stations and a small number of central stations, the above type of RoF transmission brings a significant economical advantage. Fig. 3: RF signal transmission over fibre and signal processing at the central station. A transmission from the central station to individual base stations can be made also over a single optic fibre using wavelength-division multiplexing (WDM), as shown in Figure 4. However, from a practical standpoint the dual-fibre concept is easier to implement. Fig. 4: RF signal transmission via an optic WDM connection. It makes sense to use the same antenna for signal transmission and reception at the base station where the transmission and reception signals are joined/divided via a 145 Informacije MIDEM 41(2011)2, str. 144-149 B. Batagelj, L. Pavlovic, L. Naglic, S. Tomazic: Convergence of Fixed and Mobile Networks by Radio over ... micro-wave circulator (Figure 5). In this case, the base station contains a laser, photodiode, circulator, RF amplifiers, control unit and power circuitry. Although it is all packed into a small casing, the unit is still quite complex. Fig. 5: RF signal transmission via fibre optic and transmission and reception via a single antenna. In order to reduce the number of elements, it was proposed to replace the laser, photodiode and circulator with a single semiconductor electroabsorption modulator (EAM) /7/. This device can act as both a receiver and transmitter. The advantage of such a solution is that a laser source is no longer necessary at the base station. This makes a remote antenna unit much less complex and costly /8/. A remote antenna unit can be further simplified (Figure 6) if radio coverage is limited to a small area. This eliminates the need for RF amplifiers and the electroabsorption modulator can operate without any biasing. In this case, the base station consists only of an electroabsorption modulator and antenna /9/. Fig. 6: RF signal transfer via fibre optic and the use of an electroabsorption modulator. The use of carrier re-modulation at the base station rather than a local light source is promising technique. Avoiding stabilisation and provisioning issues associated with a laser at base station is a good way of reducing installation and maintenance costs. An electroabsorption modulator integrated with a reflective semiconductor optical amplifier (R-SOA) can provide optical amplification and optical modulation in a single device /10/. As shown in Figure 7, the implementation of R-SOA with EAM into RoF system is replacing dual fibre link by only one single Fig. 7: RF signal transfer via fibre optic and the use of an electroabsorption modulator and R-SOA. It should be noted that there are certain disadvantages of processing the RF signal at the central station. Due to the broadband nature of the RF signal, it is often impossible to directly modulate the laser and therefore an external Mach-Zehnder modulator (MZM) is required. Furthermore, the amplitude modulation is highly sensitive to chromatic dispersion of the optical fibre which accumulates with the length of fibre /11/. As the optical signal is transferred across the fibre with the carrier and double sidebands, the chromatic dispersion causes a different phase delay on each of the spectral components, as shown in Figure 8. Fig. 8: Chromatic dispersion changes the phase relationship between the optical carrier and upper and lower sideband. The phase delay depends on the fibre length, modulation frequency and dispersion coefficient. The power of detected signal is length dependent /12/ ^(A/mod)00 COS izLcD / \2 \ f J mod /c o y where L is the fibre length, c is the speed of light in free space, D is the fibre dispersion coefficient, f0 is the optical carrier frequency, and fmod is the frequency of subcarrier. If the phase delay between the sidebands at the end of the fibre line is 180°, the destructive mixing on the photodiode will negate the entire RF signal, as shown in Figure 9. For an example of the standard single-mode optical fibre with a 17 ps/(nm km) dispersion at 1550 nm, a 3 dB RF signal degradation for double sideband modulation occurs at 6 km, at a 20 GHz modulation frequency. At a 60 GHz Fig. 9: Power penalty of the RF signal depending on the fibre length and modulation frequency. 146 B. Batagelj, L. Pavlovič, L. Naglič, S. Tomažič: Convergence of Fixed and Mobile Networks by Radio over Informacije MIDEM 41(2011)2, str. 144-149 modulation frequency a 3 dB degradation already occurs at 0.7 km /13/. Direct modulation is only applicable for frequencies up to 10 GHz. For higher frequencies the limiting dispersion occurrence can be reduced by using a single sideband modulation /14, 15/ with an optic filtration or specially controlled MZM. With detailed knowledge of the dispersion characteristics of the RoF system, the disruptive phenomenon can be used to one's advantage. In the special case of the optical regulation of an antenna array, the phenomenon is welcome as it enables control over the antenna array beam /16/. In cases where a high level of resistance to dispersion is desired on the connection between the central and base station, the final signal processing must once again be transferred to the base station. Another reason for this is the limiting direct modulation of the laser source. Simultaneity, warless systems which are based on orthogonal frequency-division multiplexing (OFDM) are requiring RF signal source with high stability located in temperature regulated enviroment. Because greater complexity of the base station is undesirable, the optic generation of the carrier RF signal is recommended, as shown in Figure 10. The RF signal generation through optical photomixing eliminates the need for frequency stabilisation of the local oscillator due to the thermal dependence of the oscillation frequencies. Unfortunately, in case of presence of PMD in the transmission fibre, efficiency of RF signal is reduced or even equal to zero in the worst case. Consequently, low PMD fibre is required. Fig. 10: Illustrations of RF signal generation through photomixing. With separate optic carriers, the signal is transmitted from the central station over the baseband frequency. At the remote base station, the optical signals are mixed on the photodiode, creating a RF signal suitable for frequency conversion of the data signal in the mixer. The technology which uses separate optic lines for the data signal and for mixing signal is displayed in Figure 11. All optical lines can also be joined in a single optic fibre using WDM technology. Unfortunately, power supply for amplifier and RF mixers is needed in base station location. Complication with electric power delivery can be avoided by using photonic power delivery /17/. In this case, the base station can be readily energized by high-power laser which illuminate optical energy and photovoltaic converter, as shown on Figure 12. Fig. 11: Transmission by RF signal generation. Photovoltaic cells can convert up to 50% of the incident light into electrical energy. If the wavelength of low fibre attenuation is used optical power can be transmitted up to 10 km. This approach offers total electrical isolation and independence of base station. Fig. 12: Photonic power conversion delivers electric power to base station. 3. Key elements for Radio over Fibre technology If we wish to create an RF signal through photomixing, the used photodetector needs a sufficient bandwidth for the relevant frequency area. Travelling wave photodiodes are currently the most suitable option for this /18/. The optical carriers for photomixing can be obtained from two separate lasers where the signals are joined into a single optical fibre using an optical coupler. A dual-line laser can be used, which oscillates on two wavelengths simultaneously. A heterodyne OPLL (Figure 13) allows the slave laser to be phase-locked to the master laser by a frequency deference equal to the frequency of the microwave reference. The offset frequency can in principle be arbitrary, but in practice is restricted by the bandwidth of the photodetector or microwave components. When the used optic sources are phase-locked there is no error signal at the phase detector output and the obtained RF signal is clear in terms of the spectrum and the phase noise. An electro-optical phase-locked loop /19/ is used for the phase locking of separate 147 Informacije MIDEM 41(2011)2, str. 144-149 B. Batagelj, L. Pavlovic, L. Naglic, S. Tomazic: Convergence of Fixed and Mobile Networks by Radio over ... laser sources. Even when using very narrow linewidth solidstate lasers, the complete loop delay has to be kept very small to avoid cycle slips. An electro-optic phase-locked loop is not necessary if a dual-line laser is used as the laser's structure itself ensures phase harmonisation. usable operating frequency range is above approximately 70 GHz. The calculated radiation pattern of this structure at 100 GHz is illustrated in Figure 16. Fig. 13: Heterodyne optical phase-locked loop with frequency divider. At the output of the photodetector, the issue of choosing a suitable waveguide arises due to the great bandwidth. In order to avoid the waveguide from the photodetector to the antenna, the photodiode can be placed on the antenna itself. As the antenna is much larger than the photodetector, the photodiode can be placed directly on the antenna's supply junction (Figure 14). The antenna's working frequency range needs to cover the frequency area of the RF signal coming from the photodetector. As we are dealing with a broad frequency spectrum from several GHz to several THz, the antenna needs to be broadband to accommodate this. Fig. 14: Layout of the photodetector integrated with the planar antenna. At the moment, the most appropriate option has proven to be the planar spiral antenna as it has a well-defined radiation pattern and relatively constant impedance over a broad frequency range. The spiral antenna rests on a hemispherical silicone lens (Figure 15). If the diameter of the spiral antenna is about 2 mm on a lens with the diameter of 4 - 8 mm the Fig. 15: Planar spiral antenna on a dielectric lens. The antenna emits the main beam in the direction of the lens axis through the substrate and the lens. Side beams are relatively low. The gain is around 7 dBi at 100 GHz. The antenna's impedance is relatively constant and changes between 20 Q and 80 Q, which fits well to the impedance of the travelling wave photodetector. Fig. 16: Simulated radiation pattern of the spiral antenna on a hemispherical silicon lens at 100 GHz. 4. Conclusion This article presents the convergence of mobile and fixed access network on the physical level. It describes a mobile solution based on a fibre optic access infrastructure which is standard independent. Presented convergent network 148 B. Batagelj, L. Pavlovič, L. Naglič, S. Tomažič: Convergence of Fixed and Mobile Networks by Radio over Informacije MIDEM 41(2011)2, str. 144-149 architectures are able to transfer any telecommunication protocol. With the aim of reducing the costs of a remote antenna unit of a picocell network, the solution is based on RoF technology. The RoF system transfers complex radio frequency signal processing functions from the base station to the centralised control station. However, all signal processing concentrated at central station brings some limitations manly due to fibre chromatic dispersion. Among the presented uses of fibre optical lines for the distribution of radio frequency signal from the central location to the remote antenna units, the most attractive solution involves the large-scale integration of electro optical components. A simple base station consisting only of an elec-troabsorption modulator integrated with reflective SOA and antenna is certainly the best solution and supports different types of traffic. The use of carrier re-modulation at the base station rather than a local light source has been suggested as a way of reducing installation and maintenance costs. I the case when RF signal is generated by optical mixing in base station, power supply can be delivered as photonic power what further reduce implementation costs. The presented key building blocks of the RoF system, such as the photodiode with an integrated antenna, electroab-sorption modulator, optic millimetre-wave generator with a phase-locked loop and an optic-controllable antenna have been developed as prototypes and are ready for industrialization and use in both system solutions and networks. Acknowledgements The work presented in this article was created in collaboration with the Slovenian Research Agency (ARRS) as part of the "Algorithms and optimisation procedures in telecommunications" programme and the EU project IPHOBAC "Integrated Photonic mm-Wave Functions for Broadband Connectivity" project. 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Ahmed, Overcoming chromatic-dispersion effects in fiber-wireless systems incorporating external modulators, IEEE Transactions on Microwave Theory and Techniques, vol.45, no.8, pp.1410-1415, Aug 1997. / 16/ Patrik Ritoša, Boštjan Batagelj and Matjaž Vidmar, Optically steer-able antenna array for radio over fibre transmission, Electron. Lett., Aug. 2005, vol. 41, no. 16, p. 917-918. / 17/ J.-G. Werthen, M. Cohen, Photonic Power: Delivering Power Over Fiber for Optical Networks, International Conference on Photonics in Switching, 2006, pp 1-3. / 18/ A. Stoehr, A. Malcoci, A. Sauerwald, I. Camera, R. Guesten, D. Jager, "Ultra-Wideband Travelling-Wave Photodetectors for Photonic Local Oscillators", IEEE J. Light. Tech, vol. 21, no. 12, 2003, pp. 3062-3070. / 19/ Luka Naglič, Leon Pavlovič, Boštjan Batagelj and Matjaž Vidmar, Improved phase detector for electro-optical phase-locked loops, Electron. Lett., Jun. 2008, vol. 44, no. 12, p. 758-760. dr. Bostjan Batagelj University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia Tržaška cesta 25 1000 Ljubljana Tel. 01 4768 400 Gsm. 031 31 8760 e-mail. bostjan.batagelj@fe.uni-lj.si Prispelo: 31.07.2010 Sprejeto: 24.06.2011 149 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana CVL OCR DB, AN ANNOTATED IMAGE DATABASE OF TEXT IN NATURAL SCENES, AND ITS USABILITY Andrej Ikica, Peter Peer Computer Vision Laboratory (CVL), Faculty of Computer and Information Science, University of Ljubljana, Ljubljana, Slovenia Key words: computer vision, text detection, optical character recognition, natural scenes Abstract: Text detection and optical character recognition (OCR) in images of natural scenes is a fairly new computer vision area but yet very useful in numerous applicative areas. Although many implementations gain promising results, they are evaluated mostly on the private image collections that are very hard or even impossible to get. Therefore, it is very difficult to compare them objectively. Since our aim is to help the research community in standardizing the evaluation of the text detection and OCR methods, we present CVL OCR DB, a public database of annotated images of text in diverse natural scenes, captured at varying weather and lighting conditions. All the images in the database are annotated with the text region and single character location information, making CVL OCR DB suitable for testing and evaluating both text detection and OCR methods. Moreover, all the single characters are also cropped from the original images and stored individually, turning our database into a huge collection of characters suitable for training and testing OCR classifiers. Anotirana podatkovna baza slik teksta v naravnih scenah CVL OCR DB in njena uporaba Kjučne besede: prenos radiofrekvenčnega signala prek optičnega vlakna, oddaljena antenska enota, celična arhitektura, vlakenski dostop, fiksno in mobilno zlivanje Izvleček: Detekcija teksta in optična razpoznava simbolov (OCR) na slikah naravnih scen je razmeroma novo področje računalniškega vida, pa vendar zelo uporabna na številnih aplikativnih področjih. Mnoge implementacije dosegajo spodbudne rezultate, vendar njihova evalvacija večinoma poteka na privatnih zbirkah slik, ki so težko dostopne ali celo nedostopne, zato je metode med seboj zelo težko objektivno primerjati. Naš namen je pomagati raziskovalni skupnosti pri standardizaciji evalvacije omenjenih metod. Zato predstavljamo CVL OCR DB, javno bazo anotiranih slik teksta v naravnih scenah, ki so zajete pod različnimi vremenskimi in svetlobnimi pogoji. Vse slike v bazi vsebujejo informacijo o lokacijah prisotnih tekstovnih regij in posameznih črk, kar omogoča testiranje in evalvacijo tako metod detekcije teksta, kot tudi metod razpoznave simbolov. Vsi posamezni znaki so dodatno izrezani iz originalnih slik ter individualno shranjeni, kar naredi našo podatkovno bazo ogromno zbirko znakov, primerno za učenje in testiranje klasifikatorjev OCR. 1. Introduction Due to a broad range of applicative areas, text detection and OCR in natural scene images have gained a lot of research interest in the last decade. Since the research area is just beginning to evolve, there are obviously no widely accepted standards for both evaluation methodology as well as the common evaluation database, as it is typical in other computer vision areas such as face detection and recognition /1,2/. Indeed, there already exist image databases of text in natural scenes such as the ICDAR database /3/. These collections, however, include only a couple of hundreds of images and are more or less intended for private use or for competitions, whereas our idea is to establish a public collection of thousands of images that would organically grow over time. Our approach has several advantages. First, all the existing methods can be validated and objectively compared to each other on the same dataset and against the same ground-truth data. Second, with CVL OCR DB it is easy to compare the new text detection and OCR approaches with the state-of-the-art methods. Many authors claim to achieve better results compared to other (older) methods, although they often do not explicitly reveal which datasets have been used for evaluation or they simply evaluate methods on their private datasets. Finally, CVL OCR DB is a public database, which hopefully will be expanded by a diverse number of researchers and volunteers, so all the image data will actually represent a vast variety of possible scenarios. Many researchers, unfortunately, establish their private image datasets with the drawbacks of their methods in mind. Thus, they (not being aware of) avoid integrating "worst-case scenario" images into their datasets. We already tried to avoid this issue in the process of collecting and annotating image data by intentionally including the volunteers who had no previous experience in text detection and OCR whatsoever. Therefore, the collected data were actually the images seen by an average human observer, not a computer vision expert. The results were often contrary to our expectations and included complicated fonts and styles, very complex backgrounds, characters substituted by other symbols, text skews, rotations etc. The article is organized as follows. First, the CVL OCR DB construction life-cycle is described in section 2, followed by the description of the capturing methodology in Section 3. The conceptual model of annotation and the model implementation are presented in Section 4 and Section 5, respectively. In Section 6 the annotation process is described and in Section 7 we present the practical aspects of our database and evaluation results of several text detection 150 A. Ikica, P. Peer: CVL OCR DB, An Annotated Image Database of Text in Natural .... Informacije MIDEM 41(2011)2, str. 150-154 Fig. 1. The CVL OCR DB construction life-cycle. methods on the CVL OCR DB subset. Finally, the article is concluded with the discussion and the terms for using CVL OCR DB in Section 8. 2. Construction life-cycle The CVL OCR DB construction life-cycle is divided into 6 stages as shown in Fig. 1. After defining the coarse capturing methodology, the image data was collected and organized. Through the process of collecting and organizing the image data the methodology was constantly refined in order to capture as broader set of different scenarios as possible in the best possible way. The conceptual model of annotation developed afterwards was used for the actual implementation and the ground-truth data annotation. Finally, the last stage is dissemination and usage of the database for evaluation of different computer vision algorithms. 3. Capturing methodology In the image data collecting stage both the authors and the volunteers were involved. We captured a great number of images of text in natural scenes, including images of signboards, shop names, traffic signs and jumbo posters (Fig. 2). All the images were captured at varying weather and lighting conditions with either a compact camera (up to 7 mega pixels) or a mobile phone (up to 5 mega pixels), but were eventually resized to fit the computer screen. There are three main reasons for resizing the images. First, the resized (smaller) images contain enough visual information, therefore, the original (bigger) images would unnecessarily occupy the disk space. Second, smaller images can be processed much faster. The third reason, however, lies in the fact that precise annotation (selecting bounding polygons and cropping characters) can be performed much easier on the images that do not stretch beyond the computer screen dimensions. All the collected images are divided into three main categories: "day", "night" and "artificial" (tree structure in Fig. 3). The "day" category corresponds to the images captured at daylight, the "night" category corresponds to the images captured at night time and, finally, the "artificial" category corresponds to the images captured on locations where only artificial light is present (eg. shopping centers). Further on, the "day" category is divided into 4 subcategories: "normal" (normal sunlight), "sun" (very intense sunlight), "fog" and "rain". Similarly the "night" category is divided into 2 categories: "dusk" and "night" (the actual night time). This top level structure is maintained in a directory structure (Fig. 3). Every leaf node of the diagram in Fig. 3 corresponds to the actual image repository for a given category/subcategory. In other words, all the images of the particular category/subcategory are physically stored in these repository directories. We will refer to these directories as data folders. (c) (d) Fig. 2. Examples of captured text images. Fig. 3. File organization of CVL OCR DB. Each data folder contains a list of annotation files. The annotation file naming convention is the following: The filename starts with one of the following prefixes: "d_n" (day/ normal), "d_s" (day/sun), "d_f" (day/fog), "d_r" (day/rain), "a" (artificial), "n_d" (night/dusk) and "n_n" (night, night), depending on the category/subcategory of the data folder. The prefix is followed by the underscore and a 5-digit image index (including the leading zeros). For example: an annotation file for a 325th image in the day/fog category is named as "d_f_00325". Similarly a 12345th annotation file in the artificial category is named as "a_12345". The 5-digit index has an upper bound of maximum 99,999 images in a certain data folder, which is more than enough for the purpose. 151 A. Ikica, P. Peer: Informacije MIDEM 41(2011)2, str. 150-154 CVL OCR DB, An Annotated Image Database of Text in Natural..... Every annotation file is linked to an actual image and a list of character images in it (Section 6 describes the process of getting the character images in the annotation stage). Both are stored in a subdirectory of the particular data folder. We will refer to these subdirectories as the image folders. The image folder naming convention is the same as the annotation file naming convention. The actual images in the image folders are stored as JPEG files. Their naming convention is again simple and very similar to the naming convention used so far. The full image is named after the image folder it resides in and is concluded with the "_full.jpg" suffix. For example, a full text scene image in a "d_f_00325" subdirectory is named "d_f_00325_full.jpg". Single character naming convention is a little more complicated, since the single characters can occur more than once. For instance, the text scene image in Fig. 2b contains 2 letters "C", 4 letters "a" and 3 letters "A". Every character image filename starts with a subdirectory prefix followed by the "_char___<3_digit_index>.jpg" (see dashed rectangle in Fig. 3 for details), where "lc" corresponds to the lowercase and "uc" to the uppercase. For example, if our imaginary image "d_f_00325_full.jpg" consisted of 2 letters "C", 1 letter "a" and 1 letter "A", the corresponding character image filenames would be: "d_f_00325_char_C_uc_001.jpg", "d_f_00325_char_C_uc_002.jpg", "d_f_00325_char_a_lc_001.jpg", "d_f_00325_char_A_uc_001.jpg". The "lc/uc" labels are used to avoid treating the upper and lowercase character filenames as the same filename. Without these labels some operating systems would treat "d_f_00325_char_a_001.jpg" and "d_f_00325_ char_A_001.jpg" as the same filename. Moreover, the "lc/uc" labels are a great advantage when, for example, researcher wants to find all the uppercase letters in the database. The given naming convention allows a maximum of 999 of same characters per single full image, which is more than enough for the purpose. It might seem that the proposed naming convention introduces redundant data into our methodology - the image prefixes and folder names, for example, contain the same attributes. There are two main reasons why we proposed such a naming convention. First, the category is included in the filename to exploit the operating system functionality for simple queries - all the images of a certain category/ subcategory can be obtained via simple filename operating system search. Second, we want our database to be consistent even in the case of human errors - for example, when some image files are accidentally moved to other folders. 4. Conceptual model of annotation Another added value of CVL OCR DB is the annotated ground-truth data, ie. the annotation files which correspond to the text in images. For every image in the database there exists a corresponding annotation file. As shown on the left side in Fig. 4, every annotation file ("AnnotationFile" class) is linked to the actual image ("TextScenelmg" class) and multiple single character images ("Charlmage" class) cropped from the image. Single characters can be used for OCR classifier training and testing. Fig. 5 shows an example of an image with three text regions. For clarity, cropped characters of the first region are displayed as well on the right side of the figure. Fig. 4. The CVL OCR DB conceptual model. NOKIA RICSSONi <8> MOTOROLA Fig. 5. Text regions (left) and single characters of the first text region (right). The annotation file (see the right side in Fig. 4) contains two main classes: the "Info" class and the "AllTextRegions" class. The "Info" classincludes the actual image filename ("filename"), its location ("subdir") and the size constraints (min. and max. dimensions) of the text regions present in the particular image. In the database usage stage, all the text regions detected by the text detection methods violating the size constraints are simply ignored, making the evaluation process equally fair for all the methods. "AllTextRegions" class is a list of all text regions present in the image. Each text region, namely "TextRegion" class, corresponds to the physical text region in the image and is described with a bounding polygon ("boundingPoly") and a list of characters it contains. For example, the first text region in Fig. 5 contains characters "N", "O", "K", "I" and "A". Each character "Charlnstance" in the "CharList" is described with the UTF-8 character code, its filename and again with the bounding polygon. 152 A. Ikica, P. Peer: CVL OCR DB, An Annotated Image Database of Text in Natural .... Informacije MIDEM 41(2011)2, str. 150-154 5. Model implementation Since the XML files represent a very flexible, easy-to-read data format, they are a reasonable choice for describing the annotation files. Therefore, the conceptual model was implemented in the XML Schema Definition (XSD) Language /4/. The schema defines the grammar and the XML documents that follow its rules are nothing more than words in language defined by the schema. An implementation decision was taken as well, to follow a recommendation that all tags be elements with no attributes /5/. Fig. 6 shows an XSD schema for the XML annotation files derived from the conceptual model of annotation. Fig. 6. XML implementation of the conceptual model - XSD schema for XML annotation files. 6. Annotation For the annotation purposes a program for fast and effective annotation, namely TextAnnotator, was implemented. An average user can select multiple images, mark the text regions (with bounding polygons) and crop the individual characters. The annotation program automatically stores the image data in the appropriate data/image folders and creates new XML annotation files or updates the existing. In order to preserve database consistency, all XML annotation files are validated against the XSD schema (Fig. 6). Since the images are often affected by perspective and projective transformations, the text can appear rotated and skewed. To solve these issues, a 4-point bounding polygon is chosen (instead of a rectangular bounding box) to represent the text regions. Moreover, the rotated single characters pose a serious problem to OCR classifiers, so the cropped characters can be rotated by a human annotator by simply dragging the mouse in the desired direction. Currently there are much over 1,000 annotated images of text in natural scenes in the CVL OCR DB. We encourage other researchers to participate in expanding the database by annotating and uploading new text scene images (see Discussion and URL sections of the article for participation details). 7. Using cvl ocr db in practice CVL OCR DB has an enormous practical potential, since it is a step towards standardizing the evaluation approach for text detection and OCR methods on images of text in natural scenes. It is of vital importance to be able to objec- tively compare methods on the same input images and the same ground-truth data. CVL OCR DB has already been used to compare several text detection methods /6/. We compared our proposed text detection method based on the projection profiles /7,8/ against two other text detection methods, namely Ezaki /9/ and Shivakumara /10/ methods. The evaluation results in terms of precision p, recall r and quality measure f /6/ are shown in Table 1. Table 1. Practical example of CVL OCR DB usage: evaluation results of different text detection methods (bigger number means better result). Text detection method P r f Shivakumara /8/ 58,7% 51,0% 54,6% Ezaki /7/ 58,0% 53,1% 55,4% Proposed method /4/ 70,9% 55,2% 62,1% 8. Discussion In this article we presented CVL OCR DB, a public annotated image database of text in natural scenes. CVL OCR DB has several advantages. First of all, the database is public and can therefore be expanded with new images. Second, CVL OCR DB comes with the TextAnnotator program which is easy to use and enables fast database expansion without affecting the structure and internal relationships. And finally, CVL OCR DB was constructed through several iterations and revisions, so the exceptions, special cases and boundary conditions are taken into account. It is important to understand that CVL OCR DB differs from the raw image databases that contain only images and no ground-truth data whatsoever. Our database is ground-truth annotated -not only in terms of region and character locations, but also in terms of capture and lighting conditions. The important aspect is definitely its multi-functionality, since it can serve for both text detection and OCR purposes. Our aim is to try to contribute to the research community by proposing a functional and easy-to-use framework for evaluating and comparing text detection and OCR methods. We would like to encourage the research community to participate in CVL OCR DB usage - not only for the evaluation purposes but also as active contributors who help expanding it by adding and annotating new images. All the necessary material, including text annotation program, documentation and usage agreement can be downloaded from the CVL OCR DB web portal: URL CVL OCR DB web portal: http://www.lrv.fri.uni-lj. si/~peterp/CVLOCRDB/. References /1./ Resources for Face Detection (2010). Retrieved December 20 2010 from http://vision.ai.uiuc.edu/mhyang/face-detection-survey.html#face-database 153 A. Ikica, P. Peer: Informacije MIDEM 41(2011)2, str. 150-154 CVL OCR DB, An Annotated Image Database of Text in Natural..... /2./ Face Databases (2010). Retrieved December 20 2010 from http://web.mit.edu/emeyers/www/face_databases.html /3./ S. M. Lucas, A. Panaretos, L. Sosa, A. Tang, S. Wong, and R. Young, "ICDAR 2003 robust reading competitions", Proc. of 7th Int. Conf. on Document Analysis and Recognition (ICDAR 2003), Vol. II, 3-6 August 2003, pp. 682-687 /4./ XML Schema Definition (XSD) Language (2010). Retrieved December 20 2010 from http://www.w3.org/TR/xmlschema-0/ /5./ XML tags and attributes (2010). Retrieved December 20 2010 from http://www.oasis-open.org/cover/elementsAndAttrs.html /6./ A. Ikica, P. Peer, "An improved edge profile based method for text detection in natural images", Eurocon 2011 /7./ J. Park, G. Lee, E. Kim, J. Lim, S. Kim, H. Yang, M. Lee, S. Hwang, "Automatic detection and recognition of Korean text in outdoor signboard images", Pattern Recognition Letters, 2010. /8./ T. N. Dinh, J. Park, G. Lee, "Korean Text Detection and Binariza-tion in Color Signboards", Proc. of The Seventh Int. Conf. on Advanced Language Processing and Web Information Technology (ALPIT 2008), pp. 235-240 /9./ N. Ezaki, M. Bulacu, L. Schomaker, "Text Detection from Natural Scene Images: Towards a System for Visually Impaired Persons", Int. Conf. on Pattern Recognition (ICPR 2004), vol. II, pp. 683686 /10./ P. Shivakumara, T. Q. Phan, C. L. Tan, "Video text detection based on filters and edge features", Int. Conf. on Multimedia & Expo (ICME 2009), pp. 514-517 Andrej Ikica, Peter Peer Computer Vision Laboratory (CVL) Faculty of Computer and Information Science, University of Ljubljana Tržaška 25, Ljubljana, Slovenia andrej.ikica, peter.peer}@fri.uni-lj.si Prispelo: 27.05.2010 Sprejeto: 24.06.2011 154 UDK621.3:(53+54+621+66), ISSN0352-9045 Informacije MIDEM 41(2011)2, Ljubljana ZAPISNIK OBČNEGA ZBORA STROKOVNEGA DRUŠTVA MIDEM 24. 3. 2011 Predlagani dnevni red: 1. Otvoritev občnega zbora in ugotovitev sklepčnosti 2. Sprejem predlaganega dnevnega reda ter zapisnika prejšnjega občnega zbora 3. Izvolitev delovnega predsedstva, dveh overovateljev zapisnika in volilne komisije (3 člani) 4. Poročilo o delu društva v zadnjem mandatu (S. Amon, I. Šorli, I. Pompe) 5. Finančno poročilo (I. Šorli) 6. Poročilo nadzornega odbora (F. Smole) 7. Poročilo častnega razsodišča (J. Furlan) 8. Razprava o podanih poročilih in glasovanje o razrešnici dosedanjim organom društva 9. Predlogi in volitve novih organov društva 10. Poročilo volilne komisije o izidu volitev 11. Nagovor novega predsednika in predstavitev programa dela za naslednje obdobje, predlogi članov za nadaljnje delo društva in sprejem programa dela 12. Razno 1. TOČKA: Otvoritev občnega zbora Nagovor in pozdrav gospoda prof. dr. Andreja Žemve, prodekana UL FE. Ugotovljeno je bilo, da sklepčnosti ni, zato se je počakalo pol ure. V skladu s statutom društva MIDEM je po pol ure občni zbor društva postal sklepčen. 2. TOČKA: Sprejem dnevnega reda ter zapisnika prejšnjega OZ Dnevni red je bil sprejet brez pripomb. 3. TOČKA: Izvolitev delovnega predsedstva Dr. Slavko Amon predlaga za predsednika delovnega predsedstva dr. Janeza Trontlja, za dva overovatelja dr. Janeza Krča in dr. Iztoka Šorlija. Za člane volilne komisije pa predlaga dr. Kristijana Brecla, dr. Boštjana Glažarja in g. Miho Filipiča. Sledilo je glasovanje glede predlaganih kandidatov. Predlagani so bili soglasno potrjeni. SKLEP št. 1: Občni zbor je izvolil vse zgoraj navedene kandidate. Dr. Janez Trontelj kot izvoljeni delovni predsednik prevzame vodenje občnega zbora. 4. TOČKA: Poročilo o delu društva v zadnjem mandatu (S. Amon, I. Šorli, I. Pompe) Poročilo predsednika društva (S. Amona) Dr. Slavko Amon je kot predsednik društva opisal delovanje društva med obema občnima zboroma (od 22.6.2010 do 24.3.2011). Opisal je delovanje društva, IO in sekretariata na področju izdajanja revije, organizacije konferenc, poslovanja in administracije. Omenil je sodelovanje društva z drugimi institucijami (IMAPS, CO NAMASTE, TC SEMTO). Glej priloženo poročilo. 5. TOČKA: Finančno poročilo (I. Šorli) Dr. Šorli je dopolnil predsednikovo poročilo s konkretnimi podatki. Najprej je predstavil VSEBINSKO FINANČNO POROČILO od leta 2007 do 2009. Društvo je takrat poslovalo pozitivno, s presežkom prihodkov nad odhodki. Presežek se prišteje v društveni sklad. Največji delež prihodkov predstavljajo subvencije ARRS, nato plačane kotizacije s konferenc, nazadnje šele plačane članarine. Največje stroške društva predstavljajo plačani računi za revijo Informacije MIDEM, stroški organizacije konferenc in izplačani avtorski honorarji. KONFERENCA MIDEM Dr. Šorli je nadalje predstavil zgodovino organiziranja konferenc s strani društva od leta 1992 do 2010. Od leta 1998 se na pobudo dr. Dejana Križaja na konferencah en dan nameni delavnici. Vsako leto se konferenca organizira na različni lokaciji v Sloveniji. Udeležba na konferencah je med 60-80 udeleženci (tuji in domači). Število predstavljenih referatov niha med 50 -70, več je domačih kot tujih. Zaradi tega tudi ARRS obravnava konferenco kot domačo konferenco z mednarodno udeležbo. Želja je, da se poveča udeležba na 100 udeležencev na konferenco in da se jo popularizira. Od vsega začetka se držimo cilja, da se konferenco dobro organizira in izvede od začetka do konca. Poudariti moramo tudi to, da se pred konferenco zberejo vsi referati, ki so na njej predstavljeni in se izda zbornik referatov, ki ga udeleženci konference dobijo ob prijavi na mestu konference. To se je do zdaj izkazalo za zelo dobro potezo. REVIJA INFORMACIJE MIDEM Predstavljena je bila zgodovina izhajanje revije Informacije MIDEM. Revija se je najprej imenovala Informacije SSOSD 155 Informacije MIDEM 41(2011)2, str. 155-157 (Savezni odbor za elektronske sastavne delove), nato se je preimenovala v Informacije SSESD (Strokovna sekcija za elektronske sestavne dele in materiale pri Jugoslovanski zvezi ETAN), leta 1986 se revija preimenuje v Informacije MIDEM. Od leta 1988 je dr. Šorli glavni in odgovorni urednik revije, ki ostaja vse do danes. Leta 1998 postane faktor vpliva (IF) revije od 0 različen. Faktor vpliva se izračunava že 12 let, od leta do leta pa precej variira. Revija ima nizek faktor vpliva in vedno obstaja možnost, da se ga poviša. Ob tej priložnosti je bil narejen apel na prisotne in na njihove kolege, naj v svojih prispevkih, člankih citirajo revijo MIDEM. Podana je bila tudi samokritika, da revija izhaja z zamudo zaradi kroničnega pomanjkanja časa urednika. Revija se v fizični obliki in elektronski verziji tudi pošilja v večje knjižnice (npr. Thompson Scientific, Ebsco Industries,...), kjer hranijo znanstvene publikacije. Glej priloženo poročilo. Poročilo tajnika (I. Pompe) G. Igor Pompe je predstavil strukturo trenutnih članov društva (460). Povedal je, da je na leto od 100 do 200 plačanih članarin. Društvo ima tudi elektronsko bazo članov, v kateri je 200 imen in na katere se pošiljajo razna obvestila o delovanju društva. Podal je predlog, da bi se število članov lahko povečalo preko sodelovanja oziroma včlanjevanja tudi oseb, študentov,. npr. z Univerze v Mariboru. Dobro bi bilo tudi nasploh povečati število članov v društvu. Omenil je tudi, da ima društvo status posebnega družbenega pomena, kar bi bilo potrebno vzdrževati. Prisotni niso imeli nobenih ugovorov na poročila. 6. TOČKA: Poročilo nadzornega odbora (F. Smole) V poročilu je v imenu nadzornega odbora dr. Franc Smole ugotovil, da je društvo v iztekajočem mandatnem obdobju izpolnjevalo ustaljene naloge v skladu s programom in pravili društva. Pri pregledu finančnega poslovanja ni ugotovil nepravilnosti. Glej poročilo. 7. TOČKA: Poročilo o delu častnega razsodišča v zadnjem mandatu (J. Furlan) Zaradi upravičene odsotnosti je poročilo dr. Jožeta Furlana prebral dr. Slavko Amon. Častno razsodišče v zadnjem mandatu ni zaznalo nobenih nepravilnosti pri delovanju članov društva in od članov ni dobilo nobene pobude za ukrepanje. Glej poročilo. 8. TOČKA: Razprava o poročilih Razprave ni bilo, saj ni bilo dodatnih vprašanj ali komentarjev. Sledilo je GLASOVANJE O RAZREŠNICI DOSEDANJIH ORGANOV DRUŠTVA (izvršilni odbor, nadzorni odbor, častno razsodišče, sekretariat, predsednik, podpredsednik,...) Pri glasovanju noben ni bil proti in noben se ni vzdržal. Dosedanji organi društva so bili soglasno razrešeni. Poročila so bila prav tako soglasno sprejeta (noben ni bil proti, noben se ni vzdržal). SKLEP št. 2: Občni zbor soglasno sprejema poročila za minulo obdobje in vsem organom društva se soglasno podeli razrešnica za minulo obdobje. 9. TOČKA: Predlogi in volitve novih organov društva 10. TOČKA: Poročilo volilne komisije o izidu volitev Glasovnice (priloga) so se razdelile prisotnim na občnem zboru. Po pregledu vpisanih na seznam prisotnih, je bilo število prisotnih članov 17. Izpolnjene glasovnice so se pobrale in v pregled in štetje jih je vzela volilna komisija, ki je bila izvoljena v 4. točki programa in zapisnika občnega zbora. Ugotovitve so naslednje: - v 14 primerih so bili izvoljeni vsi predlagani kandidati v skupinah izvršilni odbor društva, nadzorni odbor društva in častno razsodišče društva, - v 3 primerih je bil dodatno potrjen še kot predsednik dr. Marko Topič, - v 3 primerih dodatno potrjen dr. Franc Smole kot član nadzornega odbora društva, - v 2 primerih dodatno potrjen dr. Jože Furlan kot član častnega razsodišča, - v 1 primeru dodatno potrjen g. Franc Jan kot član častnega razsodišča. NOVO IZVOLJENI ORGANI DRUŠTVA SO : IZVRŠILNI ODBOR DRUŠTVA: predsednik društva: prof. dr. Marko Topič, univ. dipl. inž. el., UL Fakulteta za elektrotehnikopodpredsednica: prof. dr. Barbara Malič, univ. dipl. kem., Institut Jožef Stefan podpredsednik: dr. Iztok Šorli, univ. dipl. fiz., Mikroiks d.o.o., Ljubljana tajnik: Igor Pompe, univ. dipl. inž. el., upokojenec blagajnik: prof. dr. Janez Trontelj, univ. dipl. inž. el., UL Fakulteta za elektrotehnikočlan: Darko Belavič, univ. dipl. inž. el., HIPOPT-RR, d.o.o., Šentjernej 156 Informacije MIDEM 41(2011)2, str. 155-157 član: prof. dr. Bruno Cvikl, univ. dipl. fiz., UM Fakulteta za gradbeništvočlan: Leopold Knez, univ. dipl. inž. el., Iskra TELA d.d., Ljubljana član: dr. Miloš Komac, univ. dipl. kem., UL Fakulteta za kemijo in kemijsko tehnologijočlan: Jožef Perne, univ. dipl. inž. el., Zavod TC SEMTO, Ljubljana član: prof. dr. Slavko Amon, univ. dipl. fiz.; UL Fakulteta za elektrotehnikočlan: prof. dr. Miran Mozetič, univ. dipl. fiz. , Institut Jožef Stefančlan: prof. dr. Marija Kosec, univ. dipl. kem., Institut Jožef Stefan član: dr. Werner Reczek, Infineon AG, Austrija član: prof. dr. Giorgio Pignatel, University of Perugia, Italija član: prof. dr. Leszek J. Golonka, Technical University, Wroclaw, Poljska NADZORNI ODBOR DRUŠTVA: prof. dr. Franc Smole, univ. dipl. inž. el., UL Fakulteta za elektrotehnikomag. Andrej Pirih, univ. dipl. inž. el., Iskra zaščite d.o.o., Ljubljana dr. Slavko Bernik, univ. dipl. kem., Institut Jožef Stefan ČASTNO RAZSODIŠČE: zasl. prof.dr. Jože Furlan, univ. dipl. inž. el., upokojenec prof. dr. Radko Osredkar, univ. dipl. inž. el., UL Fakulteta za računalništvo in informatiko Franc Jan, univ. dipl. fiz., upokojenec SKLEP št. 2: Občni zbor potrjuje rezultate volitev in izvolitev novih članov društvenih organov za naslednje triletno mandatno obdobje. 11. TOČKA : Nagovor novega predsednika društva midem Sledil je govor novoizvoljenega predsednika društva g. Marka Topiča. Zahvalil se je dosedanjemu vodstvu, zaželel uspešno delo novi sestavi in opisal prihodnje cilje društva: - predlagal povečanje prepoznavnosti in obiska konferenc, - vzpostavitev elektronske izdaje revije - povezovanje z drugimi znanstvenimi revijami, ki imajo faktor vpliva večji kot 1, - pohitritev izdajanja revije, - izboljšati informiranje in komunikacijo društva, - povezati posamezne laboratorije preko strokovnih izletov ali sejmov, ki jih organizira posamezen laboratorij, - povečati vpetost podjetij v članstvo društva, - budno spremljanje razpisov,... Za dodatne informacije glej poročilo g. Topiča. 12. TOČKA: Razno Dr. Trontelj je dal predlog novemu vodstvu o pomlajevanju članstva tako, da mladi raziskovalci, študenti, ne bi plačevali članarine. Dr. Topič je omenil (tudi predlog novega vodstva), da bi se ob 25. letnici ustanovitve društva (1986-2011) podelila priznanja dolgoletnim članom in dosedanjim predsednikom društva. Organiziral bi se dogodek v Ljubljani (verjetno kar na Fakulteti za elektrotehniko), na kateri bi bilo organizirano vabljeno predavanje (mogoče dr. Koščeve), nato bi sledila svečana podelitev priznanj in na koncu druženje. Dogodek bi se organiziral v spomladanskem času, verjetno v mesecu maju ali juniju. Vsi prisotni so se s predlogom strinjali. Občni zbor je bil zaključen ob 15:15. Zapisala: Polona Šorli Predsednik delovnega predsedstva OZ prof. dr. Janez Trontelj Dosedanji predsednik društva Prof. dr. Slavko Amon Novoizvojeni predsednik društva Prof. dr. Marko Topič Overovitelja zapisnika: prof. dr. Janez Krč dr. Iztok Šorli PRILOGE: - poročilo predsednika MIDEM o delu društva v obdobju med občnima zboroma (22.6.2010-24.3.2011) - poročilo o delu častnega razsodišča v zadnjem mandatu - poročilo nadzornega odbora društva MIDEM - poročilo o delu društva program dela in smernice delovanja društva v prihodnje 157 Informacije MIDEM 41(2011)2, Ljubljana Informacije MIDEM Strokovna revija za mikroelektroniko, elektronske sestavine dele in materiale_ NAVODILA AVTORJEM Informacije MIDEM je znanstveno-strokovno-društvena publikacija Strokovnega društva za mikroelektroniko, elektronske sestavne dele in materiale - MIDEM. Revija objavlja prispevke s področja mikroelektronike, elektronskih sestavnih delov in materialov. Ob oddaji člankov morajo avtorji predlagati uredništvu razvrstitev dela v skladu s tipologijo za vode-nje bibliografij v okviru sistema COBISS. Znanstveni in strokovni prispevki bodo recenzirani. Znanstveno-strokovni prispevki morajo biti pripravljeni na naslednji način: 1. Naslov dela, imena in priimki avtorjev brez titul, imena institucij in firm 2. Ključne besede in povzetek (največ 250 besed). 3. Naslov dela v angleščini. 4. Ključne besede v angleščini (Key words) in podaljšani povzetek (Extended Abstract) v anglešcčini, če je članek napisan v slovenščini 5. Uvod, glavni del, zaključek, zahvale, dodatki in literatura v skladu z IMRAD shemo (Introduction, Methods, Results And Discsussion). 6. Polna imena in priimki avtorjev s titulami, naslovi institucij in firm, v katerih so zaposleni ter tel./Fax/Email podatki. 7. Prispevki naj bodo oblikovani enostransko na A4 stra-neh v enem stolpcu z dvojnim razmikom, velikost črk namanj 12pt. Priporočena dolžina članka je 12-15 strani brez slik. Ostali prispevki, kot so poljudni cčlanki, aplikacijski članki, novice iz stroke, vesti iz delovnih organizacij, inštitutov in fakultet, obvestila o akcijah društva MIDEM in njegovih članov ter drugi prispevki so dobrodošli. Ostala splošna navodila 1. V članku je potrebno uporabljati SI sistem enot oz. v oklepaju navesti alternativne enote. 2. Risbe je potrebno izdelati ali iztiskati na belem papirju. Širina risb naj bo do 7.5 oz.15 cm. Vsaka risba, tabela ali fotografija naj ima številko in podnapis, ki označuje njeno vsebino. Risb, tabel in fotografij ni potrebno lepi-ti med tekst, ampak jih je potrebno ločeno priložiti članku. V tekstu je treba označiti mesto, kjer jih je potrebno vstaviti. 3. Delo je lahko napisano in bo objavljeno v slovenščini ali v angleščini. 4. Uredniški odbor ne bo sprejel strokovnih prispevkov, ki ne bodo poslani v dveh izvodih skupaj z elektronsko verzijo prispevka na disketi ali zgoščenki v formatih ASCII ali Word for Windows. Grafične datoteke naj bodo priložene ločeno in so lahko v formatu TIFF, EPS, JPEG, VMF ali GIF. 5. Avtorji so v celoti odgovorni za vsebino objavljenega sestavka. Rokopisov ne vračamo. Rokopise pošljite na spodnji naslov. Uredništvo Informacije MIDEM MIDEM pri MIKROIKS Stegne 11, 1521 Ljubljana, Slovenia Email: Iztok.Sorli@guest.arnes.si tel. (01) 5133 768, fax. (01) 5133 771 Informacije MIDEM Journal of Microelectronics, Electronic Components and Materials_ INSTRUCTIONS FOR AUTHORS Informacije MIDEM is a scientific-professional-social publication of Professional Society for Microelectronics, Electronic Components and Materials - MIDEM. In the Journal, scientific and professional contributions are published covering the field of microelectronics, electronic components and materials. Authors should suggest to the Editorial board the classification of their contribution such as : original scientific paper, review scientific paper, professional paper... Scientific and professional papers are subject to review. Each scientific contribution should include the following: 1. Title of the paper, authors' names, name of the institution/ company. 2. Key Words (5-10 words) and Abstract (200-250 words), stating how the work advances state of the art in the field. 3. Introduction, main text, conclusion, acknowledgements, appendix and references following the IMRAD scheme (Introduction, Methods, Results And Discsussion). 4. Full authors' names, titles and complete company/institution address, including Tel./Fax/Email. 5. Manuscripts should be typed double-spaced on one side of A4 page format in font size 12pt. Recommended length of manuscript (figures not included) is 12-15 pages 6. Slovene authors writing in English language must submit title, key words and abstract also in Slovene language. 7. Authors writing in Slovene language must submit title, key words and extended abstract (500-700 words) also in English language. Other types of contributions such as popular papers, application papers, scientific news, news from companies, institutes and universities, reports on actions of MIDEM Society and its members as well as other relevant contributions, of appropriate length , are also welcome. General informations 1. Authors should use SI units and provide alternative units in parentheses wherever necessary. 2. Illustrations should be in black on white paper. Their width should be up to 7.5 or 15 cm. Each illustration, table or photograph should be numbered and with legend added. Illustrations, tables and photographs must not be included in the text but added separately. However, their position in the text should be clearly marked. 3. Contributions may be written and will be published in Slovene or English language. 4. Authors must send two hard copies of the complete contributon, together with all files on diskette or CD, in ASCII or Word for Windows format. Graphic files must be added separately and may be in TIFF, EPS, JPEG, VMF or GIF format. 5. Authors are fully responsible for the content of the paper. Contributions are to be sent to the address below. Uredništvo Informacije MIDEM MIDEM pri MIKROIKS Stegne 11, 1521 Ljubljana, Slovenia Email: Iztok.Sorli@guest.arnes.si tel.+386 1 5133 768, fax.+386 1 5133 771 158 Informacije MIDEM 41(2011)2, Ljubljana MIDEM 1 1 DRUSTVO-SOCIETY C Î Slovenia Chapter M I D E M Strokovno društvo za mikroelektroniko, elektronske sestavne dele in materiale MIDEM pri MIKROIKS Stegne 11, 1521 Ljubljana SLOVENIJA TEL.: +386 (0)1 5133 768 FAX: +386 (0)1 5133 lll Email I WWW iztok.sorli@guest.arnes.si http:||paris.fe.uni-lj .si|midem| MIDEM SOCIETY REGISTRATION FORM 1. First Name ................................................................Last Name........................................ Adress................................................................................................................................... City....................................................................................................................................... Country.....................................................................Postal Code..................................... 2. Date of Birth............................................................. 3. Education (please, circle whichever appropriate) PhD MSc BSc High School 3. Profession (please, circle whichever appropriate) Electronics Physics Chemistry 4. Company............................................................................ Student Metallurgy Material Sc. Adress City .... Country.....................................................................Postal Code Tel.: ............................................................................FAX: ........... Email............................................................................................... 5. Your Primary Job Function Fabrication Engineering Management Purchasing Facilities Consulting QA/QC Other 6. Please, send mail to a) Company adress b) Home Adress 7. I wil regularly pay MIDEM membership fee, 25,00 EUR/year MIDEM member recive Journal "Informacije MIDEM" for free !!! Signature .......................................................................Date.................... 159 Informacije MIDEM 41(2011)2, Ljubljana 160 ORGANI DRUŠTVA MIDEM - BOARDS OF MIDEM Predsednik društva MIDEM MIDEM President Prof. dr. Marko Topič, univ. dipl. inž. el., UL Fakulteta za elektrotehniko, Ljubljana, Slovenija IZVRŠILNI ODBOR MIDEM - MIDEM EXECUTIVE BOARD Podpredsednika Vice-presidents Prof. dr. Barbara Malič, univ. dipl. kem., Institut Jožef Stefan, Ljubljana, Slovenija Dr. Iztok Šorli, univ. dipl. inž. fiz., MIKROIKS, d. o. o., Ljubljana, Slovenija Tajnik Secretary Igor Pompe, univ. dipl. inž. el., Ljubljana, Slovenija Člani izvršilnega odbora MIDEM Executive Board Members Prof. dr. Janez Trontelj, univ. dipl. inž. el., UL Fakulteta za elektrotehniko, Ljubljana, Slovenija, blagajnik Darko Belavič, univ. dipl. inž. el., HIPOPT-RR, d.o.o., Šentjernej, Slovenija Prof. dr. Bruno Cvikl, univ. dipl. fiz., UM Fakulteta za gradbeništvo, Maribor, Slovenija Leopold Knez, univ. dipl. inž. el., Iskra TELA d.d., Ljubljana, Slovenija Dr. Miloš Komac, univ. dipl. kem., UL Fakulteta za kemijo in kemijsko tehnologijo, Ljubljana, Slovenija Jožef Perne, univ. dipl. inž. el., Zavod TC SEMTO, Ljubljana, Slovenija Prof. dr. Slavko Amon, univ. dipl. fiz.; UL Fakulteta za elektrotehniko, Ljubljana, Slovenija Prof. dr. Miran Mozetič, univ. dipl. fiz. , Institut Jožef Stefan, Ljubljana, Slovenija Prof. dr. Marija Kosec, univ. dipl. kem., Institut Jožef Stefan, Ljubljana, Slovenija Dr. Werner Reczek, Infineon AG, Austrija Prof. dr. Giorgio Pignatel, University of Perugia, Italija Prof. dr. Leszek J. Golonka, Technical University, Wroclaw, Poljska Nadzorni odbor Supervisory Board Prof. dr. Franc Smole, univ. dipl. inž. el., Fakulteta za elektrotehniko, Ljubljana Mag. Andrej Pirih, univ. dipl. inž. el., Iskra - Zaščite, d. o. o. , Ljubljana Dr. Slavko Bernik, univ. dipl. inž. kem., Institut "Jožef Stefan", Ljubljana Častno razsodišče Court of Honour Zasl. prof.dr. Jože Furlan, univ. dipl. inž. el.,Ljubljana, Slovenija Prof. dr. Radko Osredkar, univ. dipl. inž. el., UL Fakulteta računalništvo in informatiko, Ljubljana Franc Jan, univ. dipl. fiz., Kranj, Slovenija Sponzorji MIDEM MIDEM Sponsors JAVNA AGENCIJA ZA RAZISKOVALNO DEJAVNOST RS, Ljubljana INSTITUT "JOŽEF STEFAN", Odsekza elektronsko keramiko, Ljubljana FAKULTETAZA ELEKTROTEHNIKO - LMFE, Ljubljana FAKULTETA ZA ELEKTROTEHNIKO - LMSE, Ljubljana FAKULTETAZA ELEKTROTEHNIKO - LPVO, Ljubljana MIKROIKS,d.o.o., Ljubljana TCSEMTO, Ljubljana ISKRA ZAŠČITE d.o.o., Ljubljana RLS, d.o.o., Ljubljana Informacije MIDEM, 41(2011)2, Ljubljana, JUNIJ 2011, ISSN 0352-9045, UDK621.3:(53+54+621+66)(05)(497.1)=00 Strokovna revija za mikroelektroniko, elektronske sestavne dele in materiale Journal of Microelectronics, Electronic Components and Materials Publikacija informacije MIDEM izhaja po ustanovitvi Strokovnega društva za mikroelektroniko, elektronske sestavne dele in materiale - MIDEM kot nova oblika publikacije Informacije SSOSD, ki jo je izdajal Zvezni strokovni odbor za elektronske sestavne dele in materiale SSOSD pri Jugoslovanski zvezi za ETAN od avgusta 1969 do 6. oktobra 1977 in publikacije Informacije SSESD, ki jo je izdajala Strokovna sekcija za elektronske sestavne dele, mikroelektroniko in materiale - SSESD pri Jugoslovanski zvezi za ETAN od 6. oktobra 1977 do 29. januarja 1986. Časopis Informacije MIDEM je vpisan v register časopisov pri Ministrstvu za informiranje pod registrsko številko 809.