Preparation and acoustic properties of high-temperature acoustic emission sensor based on La₃Ga₅SiO₁₄ crystal

With the rapid development of modern industries, the high-temperature piezoelectric sensors that can work in extreme environments are in great demand. In this work, langasite (La3Ga5SiO14, LGS), as a high-temperature piezoelectric crystal with stable electro-elastic performance, is used as core element, and air and porous Al2O3 are selected as backing layers respectively to prepare two kinds of high-temperature acoustic emission (AE) sensors. The detection sensitivities at 25-500 degrees C are analyzed by the ball falling test and Hsu-Nielsen experiment. Under the condition of 25-500 degrees C, the received amplitude signals by both sensors are maintained above 90 dB stimulated by the ZrO2 ceramic ball dropping. In the Hsu-Nielsen experiment, as the temperature rising from 25 degrees C to 500 degrees C, the signal amplitude of sensor with air backing layer decays from 447 mV to 365 mV, while the signal amplitude varies from 270 mV to 203 mV for the sensor with porous Al2O3 backing layer. Significantly, compared with the bandwidth of the air-backing sensor (37-183 kHz), the sensor with porous Al2O3 backing layer broadens bandwidth to 28-273 kHz. These results show that both these AE sensors have strong and stable response ability to AE signals at high-temperature of 500 degrees C. Therefore, piezoelectric AE sensor based on LGS has great potential application in the field of high-temperature structural health monitoring.