Research On Surface Acoustic Wave Sensor And Batteryless Tire Pressure Monitoring Experiment Simulating

With the rapid growth of the car ownership and increasing demanding on automobile driving safety, Tire Pressure Monitoring System (TPMS) emerges as an essential requirement.Based on the survey of TPMS in the current domestic and international market and research on development of Surface Acoustic Wave (SAW) sensors, a new scheme of batteryless/wireless TPMS is proposed focusing on the technology of SAW sensors. This system could not only monitor the temperature and pressure in tires simultaneously, but also has the advantage of batteryless, small size and high resolution. Fundamental research has been done in this dissertation in terms of theoretics, design, manufacturing and packaging of SAW sensors, and simulating experiments have done to test the scheme of batteryless/wireless TPMS.First, research on theoretics of SAW sensors has been done. By researching on the propagation characteristic of surface acoustic wave and fundamental working principle of SAW sensor, the theoretical equation on velocity change of SAW is deducted. Moreover, characteristic of quartz substrate of SAW sensor is studied and optimum selection on SAW sensor substrate is carried out based on their pressure and temperature sensitive coefficients, effective SAW coupling coefficients and power flow angles.The real electric field of interdigital transducer (IDT) is approximately decomposed as longitudinal fields and horizontal fields. By modeling the longitudinal field circuit model and horizontal field circuit model,the equivalent circuit model of IDT and the reflectors are proposed. According to the equivalent circuit models of the IDT and reflector, the equivalent circuit models of SAW resonators are proposed. The equivalent circuit models of SAW resonators are instruction of SAW sensor's impedance design and matching net of circuits.Second, research on design, manufacturing and packaging of SAW sensors has been done. A sensor with two IDT is designed for measurement of temperature and pressure based on research on theoretics of SAW sensors, and FEA method is used for optimum design for sensors'resonators. The SAW sensors are analyzed in details, including the length of resonating cavity, parameters of interdigital transducer and reflector, as well as the metal plating. Based on the analysis and the equivalent circuit models of SAW resonators, the parameters for SAW sensor are obtained.Process of SAW devices is studied and samples of SAW sensor are manufactured. A two-layer all quartz packaging that induces low stress is proposed for SAW sensors. Quartz caps used as the upper layer of the sensor are manufactured with ultrasonic devices. With study on glass frit of low melting point and epoxy glue, different bonding methods are applied in packaging for the sensor to form a hermetical bonding. Helium mass spectrograph is used to detect the leakage rate of the sensors'packaging, and six-axes micro-tester is used to measure the sensors packaging's shear strength.Third, research on measuring circuit, antenna and matching net has been done. By analyzing the circuit of traditional measurement system, scheme of circuit with one mixer is proposed. In order to improve the precision of system, the system is designed with direct digital synthesize (DDS), high isolation RF switch and equivalent scope amplifier. By analyzing antenna characteristic index and the condition for its using, a transformative dipole antenna is designed. Matching net is design for system circuit by analyzing the impedance characteristic of SAW sensor and antenna.Last, simulating experiments are carried out to test the relation between distance and gain of antenna communication, the sensor characteristic of impedance, echo signal, and the response of temperature and pressure.