The Design Of Passive Wireless SAW Temperature Sensors

Surface Acoustic Wave (SAW) sensors are promising devices in wireless measurements due to lots of advantages such as compact and small size, high measurement precision and sensing even under the harsh environments such as high temperature, high voltage and batteryless conditions.In this paper, two typical delay-line and resonator SAW temperature sensors were comprehensively compared. To meet the need of batteryless and wireless telemetering, one-port resonator SAW temperature sensors based on four different piezoelectric materials of YZ-cut LiNbO3,128°YX-cut LiNbO3, YX-cut quartz and ST-cut quartz were designed and fabricated. Firstly, SAW velocity, temperature coefficient of frequency (TCF) and electromechanical coupling factor (K2) of four piezoelectric materials were theoretically calculated and characterized. According to theoretical study, about 50 types of SAW sensors were designed and fabricated. Finally, Q factor, temperature sensitivity, decaying waves and measurement precision of the sensors were tested and compared respectively.The results are as follows:(1) LiNbO3 based SAW temperature sensors have higher temperature sensitivity than the quartz sensors.(2) In the range of 0～80℃, YZ-cut LiNbO3,128°YX-cut LiNbO3 and YX-cut quartz based SAW sensors show the better linearity than ST-cut quartz sensors in temperature characteristics.(3) Quartz based SAW temperature sensors show larger Q factor and stronger decaying signal than LiNbO3 sensors.(4) Under the same test conditions, YZ-cut LiNbO3 sensors represent superiority of higher precision when the test distance was below 10cm, while YX-cut quartz sensors performed better when the distance was above 10cm.The results above are of significance to guide the design and fabrication of one-port SAW resonator temperature sensor in the future research.