Intelligent tires based on wireless passive surface acoustic wave sensors

The structure and principle of an intelligent tire based on wireless passive surface acoustic wave (SAW) sensors are described. The SAW sensor is made by two identical delay lines on both sides of the substrate symmetrically. In each delay line, there were two reflectors with difference distance from interdigital transducer (IDT). The sensor was hermetically sealed in an all-quartz-package (APQ) technology and embedded in the tire. It can measure the tire pressure and temperature parameters automatically. According to the measurement result, the sensor systems can estimate the tire state intelligently and present the driver an alarm when the pressure or temperature was abnormal. The theory of measuring pressure and temperature is discussed and analysis for measures with pressures from 150 kPa to 300 kPa and temperatures from 25°C to 95°C is conducted. The results of measurement agree with the theory well.