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J. Grosinger, L.W. Mayer, C. Mecklenbräuker, A.L. Scholtz:
"Antenna Design for a Car Tire";
Talk: Radar, Communication and Measurement 2009 (RADCOM 09), Hamburg, Germany (invited); 03-31-2009 - 04-01-2009; in: "RADCOM 2009", GEROTRON COMMUNICATION GmbH, Hamburg (2009).

Conventional tire pressure monitoring systems (TPMS) measure the air pressure in each tire of a car with a sensor mounted on the rim. In future, TPMS will measure additional data like tire temperature, contact area, vertical load, and slip angle. As a consequence, TPMS modules must be mounted directly at the tire tread. Furthermore, tire identification and lifecycle management via radio frequency identification (RFID) will be enabled.
To design appropriate antennas for this application it is mandatory to investigate the interaction of antennas with the tire. In order to evaluate this interaction it is important to have knowledge of the tire structure and the dielectric material properties of each rubber layer.
In this contribution the characterization of the dielectric tire materials using an open-ended coaxial probe is presented. We measure the reflection coefficients for each rubber tire layer and determine the relative permittivity and loss tangent at a specific frequency by a curve fitting method using the software tool HFSS. The dielectric properties of each rubber layer are determined for a standard and a run-flat tire.
Besides the rubber material of the tire another determining factor of the antenna parameters is the steel belt in the tire tread. To evaluate its impact we take a closer look at its appearance. The steel wires of the belt form a highly conducting lattice which strongly influences the electromagnetic wave propagation. We investigate two main effects. First, the lattice has a different behavior for different polarizations of the electromagnetic field and second, the skin effect has to be considered.
We create a simplified simulation model in HFSS of the tire tread to facilitate the antenna design process for the air pressure sensor. The single rubber layers are realized using the measured dielectric material properties. The steel belt layers are modeled as anisotropically conducting planes.
To verify this simulation model a comparison of a simulation and a measurement of a dipole antenna mounted on a part of the standard tire is presented. The input impedance of the antenna is measured and simulated versus the position of the dipole. We show that measurements and simulations are consistent and that the simulation model of the tire created in HFSS is highly applicable for antenna design.

TPMS, car tire, dielectric material properties, steel belt