Research Article Power Transmission of UHF Passive ...RFID tag Tire sidewall rubber F : e RFID tag embedded in tires. Coaxial cable Probe Tire specimen Manipulator Temperature sensor

Research ArticlePower Transmission of UHF Passive Embedded RFID in Tires

Shengbo Hu12 Bing Si3 Heng Shu12 and Jinrong Mo12

1 Institute of Intelligent Information Guizhou Normal University Guiyang 550001 China2Department of Guizhou Education Center for RFID and WSN Engineering Guiyang 550001 China3 Institute of New Technology Guizhou Academy of Sciences Guiyang 550001 China

Correspondence should be addressed to Shengbo Hu hsbnsscaccn

Received 5 August 2013 Revised 28 December 2013 Accepted 30 December 2013 Published 17 February 2014

Academic Editor Yuan Yao

Copyright copy 2014 Shengbo Hu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

UHF passive RFID tags embedded in tires have a deep impact on tire life cycle management and tire monitoring In this workwe present the power transmission of UHF passive embedded RFID in tires In UHF passive embedded RFID systems in tires thebidirectional radio link between reader and tags goes through air and tires The total path loss contains reflection loss at tire-airboundaries and attenuation loss in the tires The power transmission is based on the permittivity of tires and tire-air boundaryconditions We give an OCP method for measuring the permittivity of tires By analyzing the radio link for UHF passive RFID weestablish a model of wave propagation of UHF embedded RFID in tires and make numerical analyses Numerical analyses showthat the error of the OCP methods for measuring the permittivity of tires is small the parallel polarization and normal incidenceof wave are chosen for improving the performance of the UHF embedded RFID in tires and distance is chosen to keep powertransmission function from locating valley

1 Introduction

Acting as sensors passive RFID tags can avoid sensor nodesbulky and battery powered For that reason UHF passive tagsembedded in tires have been used widely for tire life cyclemanagement in the USA and the European Union [1 2] Tomeet the Automotive Industry Action Grouprsquos B-11 standardfor North AmericanMichelin began offering automakers theoption of purchasing tires with embedded tags [3] Besidesthe combinations of UHF passive tags embedded in tire andtire pressure monitoring are paid attention highly to improvethe reliability of tire and tire control systems [4]

However range has been one of the hardest challengesin UHF passive RFID embedded in tires because the rubbermakes it harder to read the tag When Michelin took off-the-shelf UHF passive tags and embedded them in tires theread distance dropped to less than three inches [3] The maindifference between the common RFID and RFID embeddedin tires is communication medium which attenuates RFpower from the reader in RFID embedded in tires Toimprove the range and reliability of RFID embedded intires it is of great concern to study power transmission of

wave propagation for UHF passive embedded RFID in tiresbecause the tags do not contain any battery and rely on theelectromagnetic field for both power and communicationIn this paper we present the power transmission of wavepropagation for UHF passive embedded RFID in tires andlay out the foundations for reliable communication in thisenvironment

InUHFpassive RFID systems a bidirectional radio link isestablished between reader and tags which can be classifieda forward link from the reader to tags and a backward linkfrom the tags to reader [5] Depending on the characteristicsof reader and tags the propagation channel properties likepath loss and fading the power transmission coefficient andthe channel transmissions are investigated in [5ndash7] In UHFpassive embedded RFID systems in tires the bidirectionalradio link between reader and tags goes through air and tiresThe total path loss contains several factors reflection lossdue to reflected power at tire-air boundaries attenuation lossin the tires and spreading loss which is simply due to theradiation properties of antenna Each of these factors can beanalyzed using the permittivity of tires and tire-air boundaryconditions

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2014 Article ID 897041 8 pageshttpdxdoiorg1011552014897041

2 International Journal of Antennas and Propagation

FlangeOuter conductor

Dielectric

Coaxial probe

120576lowast

Test materialInner conductor

(a) Measuring system

z

Flange 120588

2a

2b Coa

xial

prob

e

(b) Geometrymodel

Figure 1 Measuring reflection coefficients with open ended coaxialprobe

So this paper focuses on wave propagation for UHFpassive embedded RFID in tires based on the permittivityof tires and tire-air boundary conditions Hence Section 2presents how to measure the permittivity of tires Section 3describes the radio link for UHF RFID systems Section 4gives a propagation model of UHF passive embedded RFIDsystems in car tires Section 5 describes numerical calculationand discussion Section 6 concludes this paper

2 Measuring the Permittivity of Tires

21 Measuring the Permittivity Several techniques have beendeveloped for measuring the permittivity [8ndash10] Howeversome such as resonant cavity or wave-guide transmissionline cells require test hardware machining and destructiveprocessing And open ended coaxial probe (OCP) techniqueis currently one of themost popular techniques formeasuringthe permittivity OCP technique can performnondestructivebroadband (RF andmicrowave bands) and high temperaturemeasurement Its well-developed theory makes it possible toobtain sufficiently accurate results

A schematic for a coaxial open ended probe is shown inFigure 1 To reduce significantlymeasuring error thematerialbeing tested is placed in close contact with the probersquosflat end The reflection coefficient measured with a vectornetwork analyzer (VNA) is used as inverse calculation of thepermittivity of the material

An equivalent circuit of admittance model for a coaxialopen ended probe is shown in Figure 2 In Figure 2 119884

119888is

the probe characteristic admittance and 119884(120596 120576lowast

) is the loadadmittance including the inner admittance 119884

119894(120596) = 119895120596119862

119894

of the capacitance 119862119894between outer conductor and inner

conductor and the outer admittance 119884119900(120596 120576lowast

) obtained bysolving the following equation [11]

119884119900

(120596 120576lowast

) = 11989521205961205760120576lowast

[ln(119887119886)]2∬

119887

119886

int

120587

0

cos120593119890minus119895119896119903

1199031198891205931198891205881015840

119889120588 (1)

where 119896 = 120596radic1205831205761015840 120583 is the permeability 120596 is the oper-ating frequency (120588 120588

1015840

120593) are cylindrical coordinates 119903 =

[1205882

+ 12058810158402

minus 21205881205881015840 cos120593]

12 and 119886 and 119887 are respectively the

YcProbe

Ci 120576lowastC0 1205962(120576lowast)2C2

1205962(120576lowast)15C1

Figure 2 The equivalent circuit of admittance model for a coaxialopen ended probe

interior and the external radius of the probe And (1) can bethe series expansion form of (2)

119884119900

(120596 120576lowast

) =

infin

sum

119899=0

(minus1) (minus119895120596)119899+1

119862119899120576lowast(119899+2)2

(2)

where

119862119899

=2(12058301205760)(119899+2)2

1198991205830[ln(119887119886)]

2∬

119887

119886

int

120587

0

119903119899minus1 cos120593119889120593119889120588

1015840

119889120588 (3)

Equation (3) shows that 119862119899is constant For convenience (2)

can be truncated to 3 terms with the 1198620 1198621 and 119862

2 So

119884(120596 120576lowast

) can be given as below

119884 (120596 120576lowast

) = 119895120596119862119894+ 119895120596120576

lowast

1198620

+ 1205962

(120576lowast

)15

1198621

+ 1198951205963

(120576lowast

)2

1198622

(4)

where 120576lowast

1198620

is the fringing capacitance of the probe1205962

(120576lowast

)2

1198622is the fringing capacitance generated from a

test material and 1205962

(120576lowast

)15

1198621is the equivalent conductance

radiated from the probeThe load admittance 119884(120596 120576

lowast

) can be obtained from theEM wave reflection coefficient Γ(120596 120576

lowast

) using the followingrelation

119884 (120596 120576lowast

) = 119884119888

1 minus Γ (120596 120576lowast

)

1 + Γ (120596 120576lowast) (5)

Hence measuring the permittivity can be performedusing the following steps

Step 1 Using VNA we measure the four different reflectioncoefficients Γ

1 Γ2 Γ3 and Γ

4associated with the four different

frequencies using a standard material with the known per-mittivity Using (4) and (5) the four unknown parameters119862

119894

1198620 1198621 and 119862

2can be solved

Step 2 Using VNA we measure the reflection coefficientsΓ associated with some frequencies using the test materialUsing (4) and (5) the permittivity of the test material can becalculated by a suitable iterative method

22 Measurement Setup for Tires The tire sidewall and theposition of the RFID tag embedded in tire are displayed inFigure 3The tag is embedded parallel to the outer steel mesh

International Journal of Antennas and Propagation 3

Steel

Inner diameterRFID tag

Tire sidewall rubber

Figure 3 The RFID tag embedded in tires

Coaxial cableProbe

Tire specimen

ManipulatorTemperature sensor

VNAAV 3629A

ScrewThermometer

Figure 4 The OCP measurement system

at a distance that depends on the tire size and ranges from 4to 8 cm above the inner steel mesh [1]

To reduce significantly measuring error using OCP tech-nique the tire sidewall specimen has to meet the followingconditions

(i) The surface of the tire sidewall specimen has to be flatA piece of the tire sidewall is cut out and the crosssection is polished to obtain a flat surface

(ii) The specimen has to have semi-infinite thickness sothat the penetration of the fieldmust bemuch smallerthan the specimenrsquos thickness

(iii) There must not be air gaps between probe and the tiresidewall specimen

Figure 4 illustrates an OCP measurement system Thesystem consists of a VNA a thermometer a coaxial probeand a manipulator with screw for fixing the tire sidewallspecimen Tightening the screw the probe is pressed againstthe specimen until no more variation of the measurementresults is observed

23 Simulation Verifying Using HFSS Simulation verifyingusing HFSS to verify the measurement accuracy using OCPtechnique an OCP model using HFSS (high frequency

x

y

z

Air boxPort

Open ended coaxial probe

Tire sidewall material

Figure 5 OCP model based on HFSS

structure simulator) is set up to compare Given themeasuredpermittivity of tire specimen using the measuring methodspresented in Section 21 the reflection coefficient is solvedusing the OCPmodel And the simulation and measurementreflection coefficients are compared

The OCP model based on HFSS is shown in Figure 5In Figure 5 the inner and outer conductors of the probe aremade of gilded brass and the space between the inner andouter conductor is filled in Teflon dielectric material Thetire specimen is modeled as a cylinder To avoid perfectlyconducting boundaries around the tire sidewall material anair box is implemented that surrounds the whole simulationsetup

3 Radio Link for UHF Passive RFID

In passive UHF RFID systems a bidirectional radio link isestablished between reader and tags including a forward linkfrom the reader to tags and a backward link from the tagsto reader What radio link for UHF passive RFID differsfrom conventional radio is that the backward link resemblesradar link Besides the RFID tagrsquos antenna absorbs waves asa function of its load match and reemits waves as a functionof its load mismatch

31 Power Absorbing Coefficient RFID tag consists of anantenna and chip The impedance matching of tag antennaand chip strongly influences the RF power transmissionand the communication performance between reader andtags Because of IC technological limit the impedance of achip cannot be chosen arbitrarily [12] So the chiprsquos inputimpedance is designed to switch between two values betweenthe conjugate impedance called as absorbing impedance119885chip1 and other impedance called as reflecting impedance119885chip2 The quality of the impedance match can be definedby the power absorbing coefficient 120591 which is the poweraccepted by the chip and the available power 119875tag at theantenna port [5 12]

120591 =

4Re [119885ant]Re [119885chip1]

Re [119885ant + 119885chip1]2

+ Im [119885ant + 119885chip1]2 (6)


where 119885ant is the tag antennarsquos input impedance and 0 le 120591 le

1 When 120591 = 1 all available power is absorbed by the chipAnd when 120591 = 0 no available power is absorbed by the chipSo the range of frequency that 120591 reaches a demand value isdefined as the bandwidth of the tag antenna This shows thata best designed tag antenna is very important to improve theperformance of UHF passive RFID

32 Power Transmission Coefficient In a passive RFID thepower absorbed by the chip in forward link can be expressedas

119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (7)

where119875TXreader is the transmitted power from reader and119875chipmust be higher than the tagrsquos sensitivity for the tagrsquos normalwork And |119878

21|2 is the power transmitted coefficient in the

forward link depending on the antenna power transmissionof reader and tag (eg antenna gain) and the propagationchannel properties like path loss and fading [5]

The power received by the reader from the tag can beexpressed as in the backward link

119875RXreader =100381610038161003816100381611987812

1003816100381610038161003816

2

120578119875tag =100381610038161003816100381611987812

1003816100381610038161003816

2

120578100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (8)

where 120578 is the modulation efficiency which is defined as theratio of the power scattered by the tag and the power availableat the tag antenna output |119878

12|2 is the power transmitted coef-

ficient in the backward link As real propagation environmentis symmetrical |119878

12|2

= |11987821

|2

4 Model of Power Transmission ofUHF Passive RFID Embedded in Tires

41 Harmonic Waves For time-harmonic fields when themedium presents a conductivity 120590 and permeability 120583 at theoperating frequency 120596 a permittivity 120576

lowast the wave equationcan be written as a time-independent wave equation towards+119911 direction

nabla2

119864 minus 1205742

119864 = 0 (9)

nabla2

119867 minus 1205742

119867 = 0 (10)

minus1205742

= 1198962

(1 minus 119895 tan 120575) = 1205962

120583120576lowast

(11)

where 120576lowast

= 1205761015840

(1 minus 119895 tan 120575) and 119896 = 120596radic1205831205761015840 is the wave numbercorresponding to an unbounded lossless medium with a realdielectric constant 120576

1015840For uniform plane waves nabla

2

= 1205972

1205972

119911 so (9) and(10) have solutions of the form 119864119890

120574119911 and 119867119890120574119911 and the

instantaneous values for the fields are given as follows

= Re 119864119890minus120572119911

119890119895(120596119905minus120573119911)

= Re 119867119890minus120572119911

119890119895(120596119905minus120573119911)

(12)

Free space

R120579i

RFID reader

RFID tag

(a) RFID scenarios in free space

Free space

R120579i

RFID reader RFID tag

Tire

(b) RFID scenarios embedded in tire

Figure 6 RFID scenarios

where the attenuation constant 120572 and the phase constant 120573

can be expressed respectively as follows [13]

120572 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

minus 1]

12

120573 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

+ 1]

12

(13)

So the electric strength decreases with distance 119911 aregiven as

119864 = 1198640119890minus120572119911 cos120573119911 (14)

Substituting (14) into power equation we have

119875 = 1198750

1003816100381610038161003816cos 21205731199111003816100381610038161003816 119890minus2120572119911

(15)

42 Power Transmission for RFID Embedded in Tires TheRFID scenarios in space and embedded in tires are shown inFigure 6 In Figure 6 the incident angle of waves is 120579

119894

In the free space the absorbing power by the RFID tag isgiven as

119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

4120587119877)

2

119866119879119875TXreader

(16)

where 120582 is the free space wavelength 119877 is the distance fromRFID reader and 119866

119879is the gain of the tagrsquos antenna


In the scenarios embedded in tires (16) can be modifiedas

119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

41205871198771

)

2

10038161003816100381610038161198791198881003816100381610038161003816

2

119866119879

1003816100381610038161003816cos 21205731198971003816100381610038161003816 119890minus2120572119897

119875TXreader

= 120591(120582

41205871198771

)

2

119866119905119879 (119891 120579

119894 119897) 119875TXreader

(17)

where 1198771is the distance between tires and the reader 119879

119888

is electric field transmission coefficient at boundary of tiresand free space and 119879(119891 120579

119894 119897) = |119879

119888|2

| cos 2120573119897|119890minus2120572119897 is power

transmission function depending on 120579119894and the distance 119897 in

tiresWhen a plane EM wave incident at an oblique angle

on tires interface there are two cases to be consideredincident electric field has polarization parallel to the planeof incidence and incident electric field has polarization thatis perpendicular to the plane of incidence So from theboundary conditions that is continuity of tangential electricand magnetic fields at the car tire interface and using theSnellrsquos laws of reflection and refraction the 119879

119888can be derived

as follows

Case 1 Parallel polarization

119879119888

=21205781cos 120579119894

1205781cos 120579119905+ 1205780cos 120579119894

(18)

Case 2 Perpendicular polarization

119879119888

=21205781cos 120579119894

1205781cos 120579119894+ 1205780cos 120579119905

(19)

5 Numerical Analyses

51 Measuring the Permittivity of Tires A standard tire(CPC220555 R16 91V) with the known permittivity (thepermittivity is 120576

1015840

= 35 and tan 120575 = 003 at frequency866MHz) is used to determine the parameters119862

11989411986201198621 and

1198622 Using the measuring methods presented in Section 21

119862119894 1198620 1198621 and 119862

2are 000113 pF 2324 times 10ndash14 pF 1518 times 10ndash

42 pF and 16345 times 10ndash50 pF respectivelyThe measuring results for reflection coefficients in a

Smith chart are shown in Figure 7 using a test car tire (GL274A made in Guizhou Tire Co LTD China) with a vectornetwork analyzer (AV 3629A) between 100MHz and 5GHzat room temperature Using (4) and (5) the permittivity ofthe test car tire can be determined to be 120576

1015840

= 378 andtan 120575 = 0038

Measuring and simulation results can be compared usingthe methods presented in Section 23 In the OCP modelthe inner and outer radiuses of the probe are 065mmand 235mm respectively The thickness of Teflon with arelative permittivity of 120576

1015840 and tan 120575 = 0001 is 135mm Thetest tire is modeled as a cylinder with a radius of 10mmand a height of 10mm The absolute error of the real partof simulation and measuring coefficients and the absolute

90100110120

130

140

150

160

170

180

minus170

minus160

minus150

minus140minus130

minus120

80 7060

50

40

30

20

10

0

minus10

minus20

minus30

minus40

minus50minus60

minus70minus80minus90minus100minus110

000000

020

020

050

050

100

100

200

200

500

500

minus500

minus200

minus020

minus050

minus100

Figure 7 Measured reflection coefficients of a test car tire

00 1 2 3 4 5

001

002

003

004

Absolute error of real partAbsolute error of imaginary part

Frequency (GHz)

Abso

lute

erro

r

Figure 8 Absolute error values of real part and imaginary part

error of the imaginary part of these versus frequency areshown in Figure 8 And the absolute error of the simulationand measuring coefficients is shown in Figure 9 Figures 8and 9 show that there is small deviation (lt0004) betweensimulation andmeasurement So it shows that the numericalsimulation has good agreement with physical experimentand the methods measuring the permittivity of tires arefeasible

52 Effects of Incident Angle 120579119894on 119879119888 The permittivity of the

test tire is 1205761015840

= 378 and tan 120575 = 0038 at frequency 866MHzfrom Section 51The incident angle 120579

119894is 0∘sim90∘ Amagnitude

of 119879119888for the parallel and perpendicular polarization is shown

in Figure 10


0 1 2 3 4 5

001

002

003

004

Absolute error

Frequency (GHz)

Abso

lute

erro

r

Figure 9 Absolute error values

0 11 23 34 45 57 68 79 900

01

02

03

04

05

06

07

Parallel polarizationPerpendicular polarization

Tc

Incident angle 120579i (∘)

Figure 10 Effects of 120579119894on 119879119888

In Figure 10 119879119888for the parallel and perpendicular polar-

ization decreases with increasing incident angle 120579119894 119879119888for the

perpendicular polarization decreases faster than 119879119888for the

parallel polarization This conclusion can be obtained fromthe experiment in Figure 11 The experiment setup containsa reader XC-RF807 and two liner polarization antennae XC-AF26 (one is a horizontal polarization antenna and the otherone is vertical polarization) The carrier frequency of thereader is 866MHz and the power o is 30 dBmWThe gain ofthe antenna is greater than 12 dBi and the frequency range isfrom 840MHz to 868MHz The distance between GL274Atire and reader is 1m and the depth of the tag embed inthe tire is 9mm Figure 12 shows the relation between theidentification rate and angle of incidence

Figure 11 Experiment setup

02

04

06

08

1


0 10 20 30 40 50 60 70 80 900

Iden

tifica

tion

rate

Incidence angle 120579i (∘)

Figure 12 Relations between angle of incidence 120579119894and the identifi-

cation rate

So the parallel polarization and normal incidence arechosen for improving the performance of UHFRFID embed-ded in tires

53 Effects of Distance 119897 on 119879(119891 120579119894 119897) For convenience The

incident angle 120579119894is 0∘ and the permittivity of the test tire

is 1205761015840

= 378 and tan 120575 = 0038 at frequency 866MHzf A magnitude of 119879(119891 120579

119894 119897) for the distance 119897 is shown in

Figure 13In Figure 13 119879(119891 120579

119894 119897) decreases periodically with

increasing the distance 119897 in tires This conclusion canbe obtained from the experiment in Figure 11 In thisexperiment 8 GAL274A tires are used from Guizhou tirelimited company in China When the tires are vulcanizingthe depths of the tag embedded in the tire are 00mm (tag ispasted on the surface of the tire) 30mm 60mm 90mm12mm 15mm 18mm 21mm and 24mm respectively(because of the limitation of the thickness of the tire thebiggest embedded depth is 24mm) Figure 14 shows therelation between the recognition rate and the embeddeddepth 119897 It means the recognition rate of tire embedded RFID


0 005 01 015 02 025 03 035 040

005

01

015

02

025

03

035

Pow

er tr

ansm

issio

n fu

nctio

n

Distance l (cm) in tires

Figure 13 Effects of 119897 on119879(119891 120579119894 119897)

0 5 10 15 20 25 30

02

04

06

08

1

11

Iden

tifica

tion

rate

Distance l (mm) in tires

Figure 14 Relations 119897 and identification rate

system declines along with 119897 also fluctuates along with 119897This means the power transmission of tire embedded RFIDsystem declines along with 119897 also fluctuates along with 119897

So the distance 119897 is chosen to keep119879(119891 120579119894 119897) from locating

valley

6 Conclusions

From now on UHF RFID tags embedded in tires have a deepimpact on tire life cycle management and tire monitoring Sowe present the power transmission of wave propagation forUHF embedded RFID in tires

In UHF passive embedded RFID systems in tires thebidirectional radio link between reader and tags goes throughair and tiresThe total path loss contains reflection loss at tire-air boundaries So we give the OCP method for measuringthe permittivity of tires By analyzing the radio link for UHFpassive RFID we establish a model of wave propagation of

UHF embedded RFID in tires and make numerical analysesFinally we make the conclusion as follows

(i) The error of the OCP methods for measuring thepermittivity of tires is small And the methods canbe used in measuring the permittivity of tires fordesigning the UHF embedded RFID in tires

(ii) It is necessary to optimize and design the antenna oftag for the impedance matching of tag antenna andchip This can improve the performance of the UHFembedded RFID in tires

(iii) The parallel polarization and normal incidence arechosen for improving the performance of the UHFembedded RFID in tires Finally the distance 119897 ischosen to keep 119879(119891 120579

119894 119897) from locating valley

Conflict of Interests

The authors declare that they have no financial and personalrelationships with other people or organizations that caninappropriately influence their work there is no professionalor other personal interests of any nature or kind in anyproduct service andor company that could be construed asinfluencing the position presented in this paper

Acknowledgments

The authors wish to thank the editor and reviewers for theirvaluable comments corrections and suggestions which ledto an improved version of the original paper This researchis a project partially supported by the Guizhou Natural Sci-ence Foundation (Grant no 2012[38]) the National NaturalScience Foundation of China (Grant no 61362004) andGuizhou Science andTechnology InnovationGroup forRFIDampWSN

References

[1] S Basat K Lim I Kim M M Tentzeris and J Laskar ldquoDesignand development of a miniaturized embedded UHF RFID tagfor automotive tire applicationsrdquo in Proceedings of the 55thElectronic Components and Technology Conference (ECTC rsquo05)pp 867ndash870 Lake Buena Vista Fla USA June 2005

[2] RFID 24-7 USA ldquoMichelin rolls out RFID-enabled tires forLondon Olympicrdquo 1 pages 2012 httpwwwrfid24-7comarticlemichelin-rolls-out-rfid-enabled-tires-for-london-olym-pics

[3] RFID Journal USA ldquoMichelin embeds RFID tags in tiresrdquo 2pages 2012 httpwwwrfidjournalcomarticleview26911

[4] RFID Journal USA ldquoRFID chip to monitor tire pressurerdquo 2pages 2012 httpwwwrfidjournalcomarticleview9311

[5] J D Griffin and G D Durgin ldquoComplete link budgets forbackscatter-radio and RFID systemsrdquo IEEE Antennas and Prop-agation Magazine vol 51 no 2 pp 11ndash25 2009

[6] P V Nikitin and K V S Rao ldquoAntennas and propagation inUHF RFID systemsrdquo in Proceedings of the IEEE InternationalConference on RFID (IEEE RFID rsquo08) pp 277ndash288 Las VegasNev USA April 2008


[7] P V Nikitin and K V S Rao ldquoTheory and measurement ofbackscattering from RFID tagsrdquo IEEE Antennas and Propaga-tion Magazine vol 48 no 6 pp 212ndash218 2006

[8] V Komarov S Wang and J Tang ldquoPermittivity and mea-surementrdquo in The Wiley Encyclopedia of RF and MicrowaveEngineering vol 4 pp 3693ndash3711 2005

[9] C C Courtney ldquoTime-domain measurement of the elec-tromagnetic properties of materialsrdquo IEEE Transactions onMicrowave Theory and Techniques vol 46 no 5 pp 517ndash5221998

[10] S Jing D Ding and Q Jing ldquoMeasurement of electromagneticproperties of materials using transmissionreflectionmethod incoaxial linerdquo in Proceedings of the 3rd Asia Pacific Conference onEnvironmental Electromagnetics pp 129ndash135Hangzhou China2003

[11] D K Misra ldquoA quasi-static analysis of open-ended coaxiallinesrdquo IEEE Transactions on Microwave Theory and Techniquesvol 35 no 10 pp 925ndash928 1988

[12] J Grosinger and A L Scholtz ldquoAntennas and wave propagationin novel wireless sensing applications based on passive UHFRFIDrdquo Elektrotechnik und Informationstechnik vol 128 no 11-12 pp 408ndash414 2011

[13] A V Hippel Dielectrics and Waves John Wiley amp Sons NewYork NY USA 1954

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Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



FlangeOuter conductor

Dielectric

Coaxial probe

120576lowast

Test materialInner conductor

(a) Measuring system

z

Flange 120588

2a

2b Coa

xial

prob

e

(b) Geometrymodel

Figure 1 Measuring reflection coefficients with open ended coaxialprobe

So this paper focuses on wave propagation for UHFpassive embedded RFID in tires based on the permittivityof tires and tire-air boundary conditions Hence Section 2presents how to measure the permittivity of tires Section 3describes the radio link for UHF RFID systems Section 4gives a propagation model of UHF passive embedded RFIDsystems in car tires Section 5 describes numerical calculationand discussion Section 6 concludes this paper

2 Measuring the Permittivity of Tires

21 Measuring the Permittivity Several techniques have beendeveloped for measuring the permittivity [8ndash10] Howeversome such as resonant cavity or wave-guide transmissionline cells require test hardware machining and destructiveprocessing And open ended coaxial probe (OCP) techniqueis currently one of themost popular techniques formeasuringthe permittivity OCP technique can performnondestructivebroadband (RF andmicrowave bands) and high temperaturemeasurement Its well-developed theory makes it possible toobtain sufficiently accurate results

A schematic for a coaxial open ended probe is shown inFigure 1 To reduce significantlymeasuring error thematerialbeing tested is placed in close contact with the probersquosflat end The reflection coefficient measured with a vectornetwork analyzer (VNA) is used as inverse calculation of thepermittivity of the material

An equivalent circuit of admittance model for a coaxialopen ended probe is shown in Figure 2 In Figure 2 119884

119888is

the probe characteristic admittance and 119884(120596 120576lowast

) is the loadadmittance including the inner admittance 119884

119894(120596) = 119895120596119862

119894

of the capacitance 119862119894between outer conductor and inner

conductor and the outer admittance 119884119900(120596 120576lowast

) obtained bysolving the following equation [11]

119884119900

(120596 120576lowast

) = 11989521205961205760120576lowast

[ln(119887119886)]2∬

119887

119886

int

120587

0

cos120593119890minus119895119896119903

1199031198891205931198891205881015840

119889120588 (1)

where 119896 = 120596radic1205831205761015840 120583 is the permeability 120596 is the oper-ating frequency (120588 120588

1015840

120593) are cylindrical coordinates 119903 =

[1205882

+ 12058810158402

minus 21205881205881015840 cos120593]

12 and 119886 and 119887 are respectively the

YcProbe

Ci 120576lowastC0 1205962(120576lowast)2C2

1205962(120576lowast)15C1

Figure 2 The equivalent circuit of admittance model for a coaxialopen ended probe

interior and the external radius of the probe And (1) can bethe series expansion form of (2)

119884119900

(120596 120576lowast

) =

infin

sum

119899=0

(minus1) (minus119895120596)119899+1

119862119899120576lowast(119899+2)2

(2)

where

119862119899

=2(12058301205760)(119899+2)2

1198991205830[ln(119887119886)]

2∬

119887

119886

int

120587

0

119903119899minus1 cos120593119889120593119889120588

1015840

119889120588 (3)

Equation (3) shows that 119862119899is constant For convenience (2)

can be truncated to 3 terms with the 1198620 1198621 and 119862

2 So

119884(120596 120576lowast

) can be given as below

119884 (120596 120576lowast

) = 119895120596119862119894+ 119895120596120576

lowast

1198620

+ 1205962

(120576lowast

)15

1198621

+ 1198951205963

(120576lowast

)2

1198622

(4)

where 120576lowast

1198620

is the fringing capacitance of the probe1205962

(120576lowast

)2

1198622is the fringing capacitance generated from a

test material and 1205962

(120576lowast

)15

1198621is the equivalent conductance

radiated from the probeThe load admittance 119884(120596 120576

lowast

) can be obtained from theEM wave reflection coefficient Γ(120596 120576

lowast

) using the followingrelation

119884 (120596 120576lowast

) = 119884119888

1 minus Γ (120596 120576lowast

)

1 + Γ (120596 120576lowast) (5)

Hence measuring the permittivity can be performedusing the following steps

Step 1 Using VNA we measure the four different reflectioncoefficients Γ

1 Γ2 Γ3 and Γ

4associated with the four different

frequencies using a standard material with the known per-mittivity Using (4) and (5) the four unknown parameters119862

119894

1198620 1198621 and 119862

2can be solved

Step 2 Using VNA we measure the reflection coefficientsΓ associated with some frequencies using the test materialUsing (4) and (5) the permittivity of the test material can becalculated by a suitable iterative method

22 Measurement Setup for Tires The tire sidewall and theposition of the RFID tag embedded in tire are displayed inFigure 3The tag is embedded parallel to the outer steel mesh


Steel




Coaxial cableProbe

Tire specimen


VNAAV 3629A

ScrewThermometer









x

y

z

Air boxPort









120591 =

4Re [119885ant]Re [119885chip1]

Re [119885ant + 119885chip1]2

+ Im [119885ant + 119885chip1]2 (6)





119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (7)





119875RXreader =100381610038161003816100381611987812

1003816100381610038161003816

2

120578119875tag =100381610038161003816100381611987812

1003816100381610038161003816

2

120578100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (8)




12|2

= |11987821

|2




nabla2

119864 minus 1205742

119864 = 0 (9)

nabla2

119867 minus 1205742

119867 = 0 (10)

minus1205742

= 1198962

(1 minus 119895 tan 120575) = 1205962

120583120576lowast

(11)

where 120576lowast

= 1205761015840



2

= 1205972

1205972


120574119911 and 119867119890120574119911 and the


= Re 119864119890minus120572119911

119890119895(120596119905minus120573119911)

= Re 119867119890minus120572119911

119890119895(120596119905minus120573119911)

(12)

Free space

R120579i

RFID reader

RFID tag


Free space

R120579i


Tire





120572 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

minus 1]

12

120573 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

+ 1]

12

(13)


119864 = 1198640119890minus120572119911 cos120573119911 (14)


119875 = 1198750

1003816100381610038161003816cos 21205731199111003816100381610038161003816 119890minus2120572119911

(15)


119894


119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

4120587119877)

2

119866119879119875TXreader

(16)





119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

41205871198771

)

2

10038161003816100381610038161198791198881003816100381610038161003816

2

119866119879

1003816100381610038161003816cos 21205731198971003816100381610038161003816 119890minus2120572119897

119875TXreader

= 120591(120582

41205871198771

)

2

119866119905119879 (119891 120579

119894 119897) 119875TXreader

(17)


119888


119894 119897) = |119879

119888|2






as follows


119879119888

=21205781cos 120579119894

1205781cos 120579119905+ 1205780cos 120579119894

(18)


119879119888

=21205781cos 120579119894

1205781cos 120579119894+ 1205780cos 120579119905

(19)



1015840


11989411986201198621 and


119862119894 1198620 1198621 and 119862




1015840

= 378 andtan 120575 = 0038



90100110120

130

140

150

160

170

180

minus170

minus160

minus150

minus140minus130

minus120

80 7060

50

40

30

20

10

0

minus10

minus20

minus30

minus40

minus50minus60


000000

020

020

050

050

100

100

200

200

500

500

minus500

minus200

minus020

minus050

minus100


00 1 2 3 4 5

001

002

003

004


Frequency (GHz)

Abso

lute

erro

r




test tire is 1205761015840




in Figure 10


0 1 2 3 4 5

001

002

003

004

Absolute error

Frequency (GHz)

Abso

lute

erro

r


0 11 23 34 45 57 68 79 900

01

02

03

04

05

06

07


Tc








02

04

06

08

1


0 10 20 30 40 50 60 70 80 900

Iden

tifica

tion

rate



cation rate




is 1205761015840



Figure 13In Figure 13 119879(119891 120579




0 005 01 015 02 025 03 035 040

005

01

015

02

025

03

035

Pow

er tr

ansm

issio

n fu

nctio

n



0 5 10 15 20 25 30

02

04

06

08

1

11

Iden

tifica

tion

rate





valley

6 Conclusions










Acknowledgments


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Steel




Coaxial cableProbe

Tire specimen


VNAAV 3629A

ScrewThermometer









x

y

z

Air boxPort









120591 =

4Re [119885ant]Re [119885chip1]

Re [119885ant + 119885chip1]2

+ Im [119885ant + 119885chip1]2 (6)





119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (7)





119875RXreader =100381610038161003816100381611987812

1003816100381610038161003816

2

120578119875tag =100381610038161003816100381611987812

1003816100381610038161003816

2

120578100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (8)




12|2

= |11987821

|2




nabla2

119864 minus 1205742

119864 = 0 (9)

nabla2

119867 minus 1205742

119867 = 0 (10)

minus1205742

= 1198962

(1 minus 119895 tan 120575) = 1205962

120583120576lowast

(11)

where 120576lowast

= 1205761015840



2

= 1205972

1205972


120574119911 and 119867119890120574119911 and the


= Re 119864119890minus120572119911

119890119895(120596119905minus120573119911)

= Re 119867119890minus120572119911

119890119895(120596119905minus120573119911)

(12)

Free space

R120579i

RFID reader

RFID tag


Free space

R120579i


Tire





120572 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

minus 1]

12

120573 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

+ 1]

12

(13)


119864 = 1198640119890minus120572119911 cos120573119911 (14)


119875 = 1198750

1003816100381610038161003816cos 21205731199111003816100381610038161003816 119890minus2120572119911

(15)


119894


119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

4120587119877)

2

119866119879119875TXreader

(16)





119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

41205871198771

)

2

10038161003816100381610038161198791198881003816100381610038161003816

2

119866119879

1003816100381610038161003816cos 21205731198971003816100381610038161003816 119890minus2120572119897

119875TXreader

= 120591(120582

41205871198771

)

2

119866119905119879 (119891 120579

119894 119897) 119875TXreader

(17)


119888


119894 119897) = |119879

119888|2






as follows


119879119888

=21205781cos 120579119894

1205781cos 120579119905+ 1205780cos 120579119894

(18)


119879119888

=21205781cos 120579119894

1205781cos 120579119894+ 1205780cos 120579119905

(19)



1015840


11989411986201198621 and


119862119894 1198620 1198621 and 119862




1015840

= 378 andtan 120575 = 0038



90100110120

130

140

150

160

170

180

minus170

minus160

minus150

minus140minus130

minus120

80 7060

50

40

30

20

10

0

minus10

minus20

minus30

minus40

minus50minus60


000000

020

020

050

050

100

100

200

200

500

500

minus500

minus200

minus020

minus050

minus100


00 1 2 3 4 5

001

002

003

004


Frequency (GHz)

Abso

lute

erro

r




test tire is 1205761015840




in Figure 10


0 1 2 3 4 5

001

002

003

004

Absolute error

Frequency (GHz)

Abso

lute

erro

r


0 11 23 34 45 57 68 79 900

01

02

03

04

05

06

07


Tc








02

04

06

08

1


0 10 20 30 40 50 60 70 80 900

Iden

tifica

tion

rate



cation rate




is 1205761015840



Figure 13In Figure 13 119879(119891 120579




0 005 01 015 02 025 03 035 040

005

01

015

02

025

03

035

Pow

er tr

ansm

issio

n fu

nctio

n



0 5 10 15 20 25 30

02

04

06

08

1

11

Iden

tifica

tion

rate





valley

6 Conclusions










Acknowledgments


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (7)





119875RXreader =100381610038161003816100381611987812

1003816100381610038161003816

2

120578119875tag =100381610038161003816100381611987812

1003816100381610038161003816

2

120578100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader (8)




12|2

= |11987821

|2




nabla2

119864 minus 1205742

119864 = 0 (9)

nabla2

119867 minus 1205742

119867 = 0 (10)

minus1205742

= 1198962

(1 minus 119895 tan 120575) = 1205962

120583120576lowast

(11)

where 120576lowast

= 1205761015840



2

= 1205972

1205972


120574119911 and 119867119890120574119911 and the


= Re 119864119890minus120572119911

119890119895(120596119905minus120573119911)

= Re 119867119890minus120572119911

119890119895(120596119905minus120573119911)

(12)

Free space

R120579i

RFID reader

RFID tag


Free space

R120579i


Tire





120572 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

minus 1]

12

120573 = 120596(1205831205761015840

2)

12

[(1 + tan2120575)12

+ 1]

12

(13)


119864 = 1198640119890minus120572119911 cos120573119911 (14)


119875 = 1198750

1003816100381610038161003816cos 21205731199111003816100381610038161003816 119890minus2120572119911

(15)


119894


119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

4120587119877)

2

119866119879119875TXreader

(16)





119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

41205871198771

)

2

10038161003816100381610038161198791198881003816100381610038161003816

2

119866119879

1003816100381610038161003816cos 21205731198971003816100381610038161003816 119890minus2120572119897

119875TXreader

= 120591(120582

41205871198771

)

2

119866119905119879 (119891 120579

119894 119897) 119875TXreader

(17)


119888


119894 119897) = |119879

119888|2






as follows


119879119888

=21205781cos 120579119894

1205781cos 120579119905+ 1205780cos 120579119894

(18)


119879119888

=21205781cos 120579119894

1205781cos 120579119894+ 1205780cos 120579119905

(19)



1015840


11989411986201198621 and


119862119894 1198620 1198621 and 119862




1015840

= 378 andtan 120575 = 0038



90100110120

130

140

150

160

170

180

minus170

minus160

minus150

minus140minus130

minus120

80 7060

50

40

30

20

10

0

minus10

minus20

minus30

minus40

minus50minus60


000000

020

020

050

050

100

100

200

200

500

500

minus500

minus200

minus020

minus050

minus100


00 1 2 3 4 5

001

002

003

004


Frequency (GHz)

Abso

lute

erro

r




test tire is 1205761015840




in Figure 10


0 1 2 3 4 5

001

002

003

004

Absolute error

Frequency (GHz)

Abso

lute

erro

r


0 11 23 34 45 57 68 79 900

01

02

03

04

05

06

07


Tc








02

04

06

08

1


0 10 20 30 40 50 60 70 80 900

Iden

tifica

tion

rate



cation rate




is 1205761015840



Figure 13In Figure 13 119879(119891 120579




0 005 01 015 02 025 03 035 040

005

01

015

02

025

03

035

Pow

er tr

ansm

issio

n fu

nctio

n



0 5 10 15 20 25 30

02

04

06

08

1

11

Iden

tifica

tion

rate





valley

6 Conclusions










Acknowledgments


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











119875chip = 120591119875tag = 120591100381610038161003816100381611987821

1003816100381610038161003816

2

119875TXreader

= 120591(120582

41205871198771

)

2

10038161003816100381610038161198791198881003816100381610038161003816

2

119866119879

1003816100381610038161003816cos 21205731198971003816100381610038161003816 119890minus2120572119897

119875TXreader

= 120591(120582

41205871198771

)

2

119866119905119879 (119891 120579

119894 119897) 119875TXreader

(17)


119888


119894 119897) = |119879

119888|2






as follows


119879119888

=21205781cos 120579119894

1205781cos 120579119905+ 1205780cos 120579119894

(18)


119879119888

=21205781cos 120579119894

1205781cos 120579119894+ 1205780cos 120579119905

(19)



1015840


11989411986201198621 and


119862119894 1198620 1198621 and 119862




1015840

= 378 andtan 120575 = 0038



90100110120

130

140

150

160

170

180

minus170

minus160

minus150

minus140minus130

minus120

80 7060

50

40

30

20

10

0

minus10

minus20

minus30

minus40

minus50minus60


000000

020

020

050

050

100

100

200

200

500

500

minus500

minus200

minus020

minus050

minus100


00 1 2 3 4 5

001

002

003

004


Frequency (GHz)

Abso

lute

erro

r




test tire is 1205761015840




in Figure 10


0 1 2 3 4 5

001

002

003

004

Absolute error

Frequency (GHz)

Abso

lute

erro

r


0 11 23 34 45 57 68 79 900

01

02

03

04

05

06

07


Tc








02

04

06

08

1


0 10 20 30 40 50 60 70 80 900

Iden

tifica

tion

rate



cation rate




is 1205761015840



Figure 13In Figure 13 119879(119891 120579




0 005 01 015 02 025 03 035 040

005

01

015

02

025

03

035

Pow

er tr

ansm

issio

n fu

nctio

n



0 5 10 15 20 25 30

02

04

06

08

1

11

Iden

tifica

tion

rate





valley

6 Conclusions










Acknowledgments


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0 1 2 3 4 5

001

002

003

004

Absolute error

Frequency (GHz)

Abso

lute

erro

r


0 11 23 34 45 57 68 79 900

01

02

03

04

05

06

07


Tc








02

04

06

08

1


0 10 20 30 40 50 60 70 80 900

Iden

tifica

tion

rate



cation rate




is 1205761015840



Figure 13In Figure 13 119879(119891 120579




0 005 01 015 02 025 03 035 040

005

01

015

02

025

03

035

Pow

er tr

ansm

issio

n fu

nctio

n



0 5 10 15 20 25 30

02

04

06

08

1

11

Iden

tifica

tion

rate





valley

6 Conclusions










Acknowledgments


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0 005 01 015 02 025 03 035 040

005

01

015

02

025

03

035

Pow

er tr

ansm

issio

n fu

nctio

n



0 5 10 15 20 25 30

02

04

06

08

1

11

Iden

tifica

tion

rate





valley

6 Conclusions










Acknowledgments


References

















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Documents

Research Article Power Transmission of UHF Passive ...RFID tag Tire sidewall rubber F : e RFID tag embedded in tires. Coaxial cable Probe Tire specimen Manipulator Temperature sensor