The Effect of the Vehicle Body on EM Propagation in Tire Pressure Monitoring Systems

A typical wireless interface for a tire pressure monitoring system (TPMS) is designed to optimize power transfer in free space without taking the car body into account. Nevertheless, the metal rim of the wheel and the metallic components of the vehicle have a profound effect on the electromagnetic wave propagation between a sensor located in the tire and a receiver mounted on the vehicle chassis. This paper evaluates the vehicle body's effect on tire sensor transmission and propagation; relates these effects to receiver antenna packaging requirements; and describes an antenna design that takes advantage of the car body to improve the efficiency of the power transmission.