High temperature transducer using aluminum nitride single crystal for laser ultrasound detection

Abstract

In this work, a new ultrasound nondestructive testing (NDT) method based on laser-generated Lamb wave detection was proposed for high temperature (HT) NDT. Lamb waves were introduced to a stainless steel plate by the Nd:YAG pulsed laser at one point and detected by aluminum nitride (AlN) transducer at a distant position. The fundamental symmetric (S 0 ) and antisymmetric (A 0 ) mode Lamb waves were successfully propagated in the thin stainless steel plate. The time-of- flight (TOF) of the S 0 and A 0 mode waves proportionally increased with the distance (D) between the laser source and the sensor, and almost no attenuation of the amplitude was observed. For the HT NDT experiment, AlN single crystal was adopted as the ultrasonic sensor material due to its high thermal resistance of the dielectric and piezoelectric constants at the elevated temperature up to 800 °C. The combination of non-contact, portable laser source as a Lamb wave generator and temperature-robust NDT sensor made of AIN has shown its great capability to detect the Lamb waves at elevated temperatures.