A multi-frequency wireless passive pressure sensor was developed for tire pressure monitoring system. The applied sensor was fabricated with SAW delay lines on a membrane, which produced enhanced sensitivity and accuracy by means of multiple frequency Continues Wave. The SAW elements operate at two frequencies in 434MHz band. The pressure is determined by calculating the reflective phase difference between the two frequencies. This new method avoids phase ambiguity and temperature dependence due to large membrane bending and temperature variation, and therefore enhances the sensor sensitivity and accuracy. In this paper, the implementation of the Tire Pressure Monitoring System (TPMS) comprising remote sensor fabrication, interrogator structure and signal processing algorithm were described. Issues about sensor calibration were also discussed. This sensor attained superior high pressure sensitivity and lower system complexity compared to conventional SAW sensors, and is very suitable for TPMS.
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