Comparison of y/36°-cut and z-cut lithium niobate composites for high temperature ultrasonic applications

Within the non-destructive testing community there is increasing interest in high temperature ultrasonic probes and arrays. One reason for this interest is a strong financial incentive: Inspections on high temperature plant could be carried out at or near the operating temperature and costly down time would therefore be reduced.

Lithium niobate with its Curie temperature of 1200°C has been of great interest for use in piezoelectric ultrasonic transducers. This paper explores the potential of lithium niobate–cement composite materials for high temperature transducers and arrays. Composites made from two different crystalline cuts of lithium niobate are compared in transmit/receive tests at temperatures up to 500°C. The composites were permanently in direct contact with the mild steel block used for these tests. y/36°-cut lithium niobate showed higher signal to noise ratio than z-cut but also a longer ring down time of the pulse. Furthermore, tests of the composites in a phased array configuration using a commercial phased array controller are reported at temperatures up to 300°C for the first time. The performance of z-cut lithium niobate composites in phased array tests is superior to that of y/36°-cut composites. Transducer performance, sensitivity, temperature stability and array resolution capability at these temperatures are discussed.