Increasing of RFID system read range

Inc easing o RFID sys em ead ange 171 INCREASING OF RFID SYSTEM READ RANGE P. Ves enický Depa men o Con ol and In o ma ion Sys ems, Facul y o Elec ical Enginee ing, Uni e si y o Žilina, Uni e zi ná 1, 010 26 Žilina, Slo akia e-mail: pe e . es enicky@ el.u c.sk Summa y This pape desc ibes some compu a ions needed o inc ease RFID sys em ead ange wice wi hou any changes in RFID eade . The inc easing o ead ange is done only by p ope selec ion o RFID ma ke pa ame e s – coil diame e and numbe o u ns. Ano he way – gene a ing s onge magne ic ield om eade – can no be used because equi emen s o some limi a ions gi en by alid s anda ds mus be aken in o accoun . 1. INTRODUCTION Two yea s ago he pape s [1] and [2], which desc ibe solu ion o some echnical p oblems o digi al RFID ma ke and eade (loca o ) de elopmen we e published. Pa ame e s o de eloped loca o a e ully compa able wi h simila equipmen s p oduced in USA and Ge many. Ma ke can be loca ed om dis ance o 2 m and iden i ica ion code om RFID chip in ma ke can be ead om dis ance o 1.5 m. This pape analyzes possibili ies how o inc ease he ead and localiza ion anges wice ( om 1.5 m o 3 m) because some enginee ing ne wo ks (mos ly wa e and sewe age pipes) ma ked by RFID ma ke s a e bu ied mo e han 3 m unde g ound su ace. A he same ime alid s anda ds which limi magne ic ield in ensi y gene a ed by loca o mus be obse ed so ha he equipmen could be ope a ed unde Gene al License VPR-06/2005 issued by Telecommunica ion O ice o Slo ak Republic. 2. LIMITS FOR THE RADIATED MAGNETIC FIELD Fo RFID applica ions in used equency band om 80 o 150 kHz nex s anda ds and egula ions a e accep ed: • Gene al License VPR-06/2005 issued by Telecommunica ion O ice o Slo ak Republic • Recommenda ion ERC/REC 70-03, annex 9, issued by ERC (Eu opean Radiocommunica ions Commi ee) • Decision ERC/DEC/(01)13 issued by ERC • S anda d ETSI EN 300 330-1 issued by ETSI [3]. Tab. 1. Magne ic ield limi s a 10 m dis ance F equency [kHz] HMAX [dBµA/m] HMAX [µA/m] 83.0 42.0 125.9 101.4 42.0 125.9 121.6 58.8 871.0 134.0 58.4 831.8 145.7 37.7 76.7 The limi s o adia ed magne ic ield measu ed a 10 m dis ance om loca o an enna and o di e en wo king equencies a e shown in Tab. 1. These limi s conside an enna adius LT =0.1 m. 3. MAGNETIC FIELD GENERATED BY LOCATOR T ansmi e an enna o loca o gene a es magne ic ield wi h in ensi y 322 )(2 )( x SIN xH LT LTLLT L + = π [A/m] (1) whe e indi idual symbols deno e: - ansmi e coil numbe o u ns N LT =50 - diame e o ansmi e coil LT =0.1 m - a ea o ansmi e coil S LT =0.0314 m 2 - ansmi e coil cu en I L =0,5 A - dis ance om ansmi e coil x These pa ame e s we e chosen so ha limi s gi en in Tab. 1 a e ul illed, i. e. H L (x)=42 dBµA/m o x=10 m o all wo king equencies (no e: o equency 145.7 kHz he limi is lowe ed o 37.7 dBµA/m). Dependence o in ensi y H L (x) on dis ance x is shown in nex g aph (Fig. 1) and i gi en limi s mus be ul illed, he in ensi y canno be in luenced by any means. Fig. 1. Magne ic ield in ensi y gene a ed by loca o . Ad ances in Elec ical and Elec onic Enginee ing 172 4. VOLTAGE INDUCED INTO MARKER The magne ic ield wi h in ensi y gi en by (1) induces in o ma ke ol age )()( xHSNQxU LMMMM µω = [V] (2) whe e - ma ke coil numbe o u ns N M =35 - ma ke a ea S M =0.0314 m 2 - quali y ac o o LC ci cui Q M =70 - pe meabili y µ=4π.10 -6 H/m - ci cula equency ω=637 k ad/s Nex g aph shows dependency o ol age U M (x) on dis ance x. A 1.5 m he ol age is 2.26 V and his alue is su icien o supplying he RFID chip bu in dis ance x=3 m he ol age is insu icien (only 0.28 V). Ra io o hese wo alues is ( ) ( ) 96,7 3 5,1 = M M U U Fig. 2. Vol age induced in o ma ke and he e o e o co ec supplying o RFID chip a 3 m dis ance he induced ol age mus be 8 imes inc eased. Analysis o o mula (2) shows ha i can be done only by inc easing o numbe o u ns N M and/o a ea S M . The quali y ac o canno be inc eased o he sake o uned LC ci cui pa asi ic ea u es and o equi ed equency bandwid h, µ and ω a e cons an and H L (x) is limi ed by s anda d [3]. 5. CHANGE OF COUPLING FACTOR BETWEEN MARKER AND LOCATOR COILS AND ITS INFLUENCE ON INDUCTIVITY The coupling ac o depends on geome ical a angemen o bo h coils (Fig. 4) and is gi en by o mula (3) [4, 5], whe e M is ma ke coil adius and θ is angle be ween coils. Acco ding o (3) he coupling ac o a dis ance x=1.5 m is k(1,5)=2,94.10 -4 and o x=3 m he alue o k(3)=3,70.10 -5 , i. e. i is 8 imes smalle (Fig. 3). I we wan o keep he coupling ac o a longe dis ance he ma ke adius M in (3) mus be 4 imes inc eased. 2 3 22 22 ).(. cos.. )( x xk LTMLT MLT + = θ [-] (3) Fig. 3. Coupling ac o θ  M LT x Fig. 4. Geome ical a angemen o coils. The induc i i y o ci cula coil is (acco ding o [4])         = 0 9,1 ln... NL M MMM µ [H] (4) whe e 0 is conduc o adius. I he coil adius M is 4 imes inc eased he induc i i y is inc eased by ac o 4.ln4 i. e. 5.55 imes. I he o iginal induc i i y has o be kep , i mus be compensa ed by numbe o u ns N M dec eased by ac o 5.55 1/1.9 i. e. 2.46 imes. 6. CONCLUSION Fo doubling RFID ma ke ead ange om 1.5 m o 3 m hese changes a e needed: • The ma ke diame e mus be 4 imes inc eased ( om o iginal alue o 20 cm o 80 cm). • Numbe o u ns mus be dec eased 2.46 imes ( om o iginal alue o 35 o 14 u ns). Inc easing o RFID sys em ead ange 173 Then he induced ol age (2) a dis ance 3 m will be 1.82 V. This is su icien o co ec supplying o he RFID chip. Nei he he coupling ac o (3) no induc i i y (4) will no be essen ially changed. Expe imen al es ing o big ma ke has no been pe o med ye and will be done in u u e. Ano he ques ion is p ac ical usabili y o so big ma ke – manipula ion, mechanical esis ance, equi emen o wide exca a ion e c. and p ice. REFERENCES [1] Ves enický, P.: Op imiza ion o Selec ed RFID Sys em Pa ame e s. AEEE 3, 2004, No. 2, pages 113-114. ISSN 1336 – 1376) 483. [2] Ves enický, P.: Solu ion o Some Technical P oblems in Ma ke and Ma ke Loca o De elopmen . Communica ions 6, 2004, No. 4, pages 103-106, ISSN 1335-4205 [3] Final d a ETSI EN 300 330-1 V1.5.1. Elec omagne ic compa ibili y and Radio spec um Ma e s (ERM); Sho Range De ices (SRD); Radio equipmen in he equency ange 9 kHz o 25 MHz and induc i e loop sys ems in he equency ange 9 kHz o 30 MHz; Pa 1: Technical cha ac e is ics and es me hods [4] Geh ing, U., Roz, Th.: RFID made easy. EM Mic oelec onic-Ma in SA. Ma in, Swi ze land, 2000 [5] íž, R., Ško pil, V.: ADSL Coppe Loop P equali ica ion. P oceedings o he In e na ional Con e ence "Resea ch in Telecommunica ion Technology 2000". VSB- TU, Os a a, 2000. Pages 13 – 16. ISBN 80- 7078-817-8