Passive Saw Temperautre And Pressure Sensor Based On Tire Pressure Monitoring System

In this dissertation, according to the need in TPMS sensor, a deep and systematic study on the design, analysis, optimization and test of TPMS sensor is made, which is based on a novel passive SAW temperature and pressure sensor. The main contents of this dissertation are consisted of the following parts.Firstly, the design methodology of the temperature and pressure sensor based on the SAW delay line theory is studied. With this new design methodology, which is in a non-traditional way, the sensor is able to measure temperature and pressure simultaneously. The sensor is designed in two direction reflectors method, i.e. the reflectors are placed in the two directions of the SAW caused by IDT, which is more energy efficient and obtains higher signal/noise ratio compared with traditional methods. By using of a weighted factor in the temperature and pressure calculation of SAW sensor, the effect of the temperature on the phase shift can be eliminated, so the phase shift induced by the pressure can be detected independently by the sensor. The function between the temperature pressure and RF pulse echo signal of SAW sensor are derivate, therefore, with this novel design, the SAW sensor is capable of measuring both the temperature and the pressure simultaneously and accurately.Secondly, the piezoelectric material character and MEMS fabrication method are studied deeply. Through the comparison among the different piezoelectric materials, and the temperature and pressure measurement requirement of the SAW sensor, Y-Z cut LiNbO3 was used as the substrate material of the sensor which has the good temperature coefficient, high electromechanical coupling coefficient, high-volume production capacity and material stability. The SAW sensor is made by this substrate through the MEMS processing technology, according to the detail parameters which can be achieved from the theory analysis.Finally, analysis method of RF pulse signal and the test result for the SAW sensor are studied deeply too. The character of the RF pulse signal is analyzed. RF pulse echo signal affected by the different RF pulse access signal widths are discussed. And RF pulse echo signal affected by the different RF pulse access signal frequency is argued too. The most suitable RF pulse signal is achieved by theoretical analysis and used in the sensor test. According to the comparison of the actual test results and theoretical analysis of data, the data coincide with each other. The actual test results showing the echo signal energy are better than traditional sensors. It is more suitable for the data processing of the signal.This dissertation starts from the theoretical model, then does the simulation calculation, building the TPMS sensors test platform, fabricating the SAW sensor and according the test data to amend and improve the theoretical model. Through the above procedures, the performance of passive SAW temperature and pressure sensor is optimized. The sensor can measure, analyze and process the temperature and pressure information.In the area of TPMS, the reliability and durability are really demanding. The reported sensor has its practicability and potential market with its advantages of simple structure, light, and wireless and passive working mode. The analysis and research of this dissertation based on the SAW delay line theory not only is used in the temperature and pressure sensor, but also is used in the other sensing fields to compensate the impact of the temperature on the device, so the analysis of this theory has a certain universal.