Study on Electromagnetic Wave Propagation Characteristics in Rotating Environments and Its Application in Tire Pressure Monitoring

During parameter acquisition of rotating components, wireless data transmission is an efficient way. In this paper, electromagnetic (EM) wave propagation characteristics in rotating environments are preliminarily studied in order to provide a strong theoretical support for developing high-performance radio monitoring systems in rotating environments. The mathematical formulation of signal wave propagation between the transmitting antenna and the receiving antenna in time-dependent rotating motion is derived. The Doppler frequency shift and the EM wave polarization characteristics in rotating environments are presented and analyzed. The two-ray propagation model in rotating environments is proposed, and the validity of the model is verified by experimental results. Taking tire pressure monitoring system (TPMS) as a typical example, key parameters affecting wireless data transmission from a rotating transmitting antenna are investigated, and system performance enhancement strategies are proposed. Power transmission tests were conducted on a TPMS operating at different frequencies and different rotating radii relative to wheel rotation axis. The test results show that the path loss and the path loss fluctuation sharpness increase with the operating frequency and the rotating radius. Moreover, the path loss for most rotation angle values decreases drastically at lower frequencies and lower radii. Wireless data transmission tests were implemented for both the improved TPMS and the old TPMS. The test results show that the receiving probabilities of successful data frame transmission are improved greatly.