High-temperature (>500/spl deg C) ultrasonic transducers: an experimental comparison among three candidate piezoelectric materials

High-temperature piezoelectric crystals, including YCa₄O(BO₃)₃, LiNbO₃, and AlN, have been studied for use in ultrasonic transducers under continuous operation for 55 h at 550°C. Additionally, thermal ratcheting tests were performed on the transducers by subjecting the crystals to heat treatments followed by ultrasonic performance testing at room temperature and 500_°C. The changes resulting from the heat treatments were less than the statistical spread obtained in repeated experiments and were thus considered negligible. Finally, in situ measurements of the pulse-echo response of YCa₄O(BO₃)₃ were performed at temperatures up to 950°C for the first time, showing stable characteristics up to these high temperatures.