Pressure and Temperature Microsensor Based on Surface Acoustic Wave in TPMS

The tire pressure monitoring system (TPMS) can not only make the driver more safety, but also save fuel and protect the tire. Tire safety is attracting the driver's attention, the United States had developed laws to enforce the TPMS installation in the car. In this paper, the basic structure and the implement method of TPMS are introduced. The SAW theory and some surface acoustic wave (SAW) temperature and pressure sensors which suit for the TPMS application are illustrated, because the passive sensor is becoming the focus in the TPMS research field. Passive SAW sensor is the good choice for TPMS, according to its wireless, passive, small size, zero age rate etc. The wireless passive SAW TPMS is one of the most important research direction. For the typical applications of automotive TPMS, a novel microsensor based on SAW is reported in this paper. The kernel structure and design theory of this sensor with a single sensing unit are introduced. With the theory of SAW delay line, the effects of temperature and pressure on the microsensor were able to be reflected by the variations of the radio frequency (RF) echo signals. The accurately measured temperature and pressure values were obtained by using of a weight factor in the data process. The excellent agreement between the pressure and temperature results measured by the sensor and the direct measurement data is presented. The practical results in the certain ranges of pressure and temperature demonstrated that the microsensor is able to measure temperature (0kPa200kPa) and pressure (20oC-100oC) at the same time. For SAW sensors the temperature measurement accuracy can reach 0.05oC, and the pressure measurement accuracy can reach 7.2kPa. In the areas of TPMS, where reliability and durability are really demanding, the reported microsensor has its practicability and potential market with its advantages of simple structure, and wireless and passive working mode.