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

High-temperature piezoelectric crystals, including YCa
₄
O(BO
₃
)
₃
, LiNbO
₃
, 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 YCa
₄
O(BO
₃
)
₃
were performed at temperatures up to 950°C for the first time, showing stable characteristics up to these high temperatures.