Determining the dielectric properties of a car tire for …...' = 1.5, tan(δ) = 0.003 Tread: Sidewall: Simulation model to evaluate influences of the tire on the antenna parameters

INSTITUT FÜRNACHRICHTENTECHNIK UNDHOCHFREQUENZTECHNIK

Determining the dielectric properties of a car tire for an advanced tire monitoring

system

Jasmin Grosinger

Vienna University of TechnologyInstitute of Communications and Radio-Frequency

Engineering

VTC2009-Fall21.9.2009

INSTITUT FÜRNACHRICHTENTECHNIK UNDHOCHFREQUENZTECHNIK Overview

• Advanced tire monitoring system

• Dielectric material properties

• Measurement method

• Simulation model

• Extraction of material properties

• Results

• Conclusion

28.08.2009 2Jasmin Grosinger


Advanced tire monitoring system

• ATMS sensor module is mounted directly on the tire tread to measure tire properties– Pressure– Temperature– Contact area– Vertical load– Slip angle

• Radio frequency identification (RFID) functionality support lifecycle management and tire identification Source: FIT-IT project proposal, Intelligent Tire


Strong interaction of antenna and tire: Investigation of tire structure and dielectric material properties of rubber


Dielectric material properties

Characterization of the lossy dielectric tire rubber:


rrr jε ′′−ε′=ε

Measure of how much the electric field is changed

Measure of how lossy the material is

r

r)tan(ε′ε ′′

=δLoss tangent:

Complex relative permittivity: ED r0εε=

D ... displacementE ... electric field strengthε0 ... permittivity of free space


Tire specimenOpen-ended coaxial probe

Test cable

Micromanipulator

Measurementmethod

Open-ended coaxial probe technique:– Measurement of the reflection coefficients of the different layers at the

end of a coaxial probe with a vector network analyzer– Field at the end of the probe fringes into the material depending on the

dielectric properties



Simulationmodel

Determination of dielectric properties through the relation between the reflection coefficient and the complex permittivity by solving the electromagnetic field at the end of the probe using HFSS (high frequency structure simulator by Ansoft Corporation)


Tire material

Air box

Port

Open‐endedcoaxial probe

HFSS design:

INSTITUT FÜRNACHRICHTENTECHNIK UNDHOCHFREQUENZTECHNIK Simulation

Effect of dielectric properties on reflection coefficients versus frequency displayed in Smith charts:

28.08.2009 Jasmin Grosinger 7

εr'=5, tan(δ)=0 εr'=15, tan(δ)=0εr'=15, tan(δ)=0.1


Extraction of relative permittivity

Dielectric parameters of the tire material are varied until the simulated and the measured reflection coefficients are equal for a specific frequency (curve fitting)


Deviation caused by dispersive rubber material

S ... reflection coefficient

INSTITUT FÜRNACHRICHTENTECHNIK UNDHOCHFREQUENZTECHNIK Results

Dielectric properties of a standard tire (Continental Premium Contact 2 205/55 R16 91H)


εr' = 6.1, tan(δ) = 0.17

εr' = 3.5, tan(δ) = 0.03

εr' = 1.5, tan(δ) = 0.003

Tread: Sidewall:

Simulation model to evaluate influences of the tire on the antenna parameters (input impedance, efficiency, gain)

Simulation model of tread:

INSTITUT FÜRNACHRICHTENTECHNIK UNDHOCHFREQUENZTECHNIK Conclusion

• To design appropriate antennas for an ATMS module in the car tire the tire structure and the electromagnetic material properties of the tire rubber have to be evaluated

• Determination of the dielectric material properties of the tire rubber is done with an open-ended coaxial probe technique

– Reflection coefficient measurement

– Numerical curve fitting in HFSS

• Design of a simulation model of the tire tread to investigate antennas directly attached to tire rubber to achieve appropriate input impedance, bandwidth, gain, and efficiency



Backup


INSTITUT FÜRNACHRICHTENTECHNIK UNDHOCHFREQUENZTECHNIK Tire properties

• Contact area depends on the vertical load

• Slip angle: angle between a rolling wheel‘s actual direction of travel and the direction towards which it is pointing


INSTITUT FÜRNACHRICHTENTECHNIK UNDHOCHFREQUENZTECHNIK Tire structure


Source: http://www.conti-online.com

1) Tread2) Cap ply3) Steel belts4) Radial ply5) Airtight rubber interior6) Sidewall7) Chafer reinforcement8) Bead chaffers9) Bead


Steel belt in the tire tread


• Appearance:− Two steel belt layers draw an

angle of about 50°

− 0.3 mm diameter of steel wires

• Anisotropic current flow

• Strong influence on the wave propagation through the tire tread


Dielectric material proprties

Arrangement of the constituent molecules in the dielectric material is changed as a reaction to an external electric field (total electric field is reduced).


http://lightandmatter.com


Open-ended coaxial probe technique

Preconditions:

– Flat surface: polished piece of tire showing the rubber layer

– Semi-infinite thickness: sample of the rubber must be thick enough to appear infinite to the probe

– No air gaps between probe and specimen: achieved with mircrmanipulator

– Non-magnetic material: μr≈1

– Linear, homogenous, and isotropic material



Fringing electric field


Documents

Determining the dielectric properties of a car tire for …...' = 1.5, tan(δ) = 0.003 Tread: Sidewall: Simulation model to evaluate influences of the tire on the antenna parameters