Intelligent Tire Pressure And Temperature Monitor System Based On Surface Acoustic Wave Technology

China is becoming the largest car market of the world,the existing tire pressure mornitor system(TPMS)at home and abroad mainly adopts active sensors,there is a shortage of the need to replace the battery on a regular basis,and the existing TPMS is not suitable for extreme environments such as flammable and explosive.Surface acoustic wave(SAW)technology can solve these problems with its nature of wireless and passive.Based on the background,the paper studies the intelligent tire pressure and temperature monitoring system based on SAW technology.Firstly,the structure of SAW sensor,echo response characteristics and the principle of pressure and temperature sensor were analyzed.At the same time,based on the coupled wave equation and partial wave theory,the cut type optimization of quartz piezoelectric substrate was carried out.According to the frequency strain coefficient and frequency temperature coefficient,suitable cut shape was choosed to fabricate pressure and temperature sensors.Secondly,the structure design and performance test of the sensor were carried out.Three SAW resonators were selected as pressure measurement,temperature measurement and reference;the pressure was measured in the form of a differential between the pressure resonator and the reference resonator,and the temperature was measured by the difference between the temperature resonator and the reference resonator.COMSOL was used to conduct the mechanical simulation on the circular beryllium bronze film,and the most suitable adhesive position of the pressure resonator was selected.Sensors were fabricated and impedance matching was performed,in order to minimize the reflection energy of high frequency signal.The echo loss of the sensor was measured,and the pressure and temperature were calibrated.Simultaneously,the linearity and sensitivity of the sensors were analyzed.Next,the reader was designed,the transmit chain with three local oscillator sources was presented,and three SAW sensors were excited simultaneously to improve the real-time measurement.According to the large attenuation of the signal caused by tire rubber and metal wheel hub in practical application,a super heterodyne receive chain with radio frequency amplification and intermediate frequency amplification was designed.In order to solve the problem of low signal-to-noise ratio(SNR)of echo signal,the singular value decomposition(SVD)denoising algorithm was designed.According to the lack of spectral resolution due to the small number of sampling points,an algorithm with time domain zero compensation and frequency domain cubic spline interpolation fitting were used to improve the spectral resolution.Finally,the performance of the system was verified by experiments.A wireless testing system for a single sensor was set up,and the echo signal of the sensor at different positions was analyzed by rotating tire.At the same time,the wireless performance of the reader was presented,the accuracy of pressure measurement is about ±0.2bar,the precision of temperature measurement is about ±0.5 ?,and the real time is about 7 times per second.According to the actual vehicle tire distribution,a testing system was set up,and the pressure and temperature of the four groups of sensors were monitored in real time by polling.