Ultrasonic transducers for high temperature applications

There is an increasing demand ultrasonic transducers to work at high temperatures. Transducers operating in the range from 400 to 1000°C are being applied in the power, process, automotive and aeroengine industries, as well as in materials research. To date, the majority of high temperature transducer designs have been based on adaptations of conventional single and dual-element probes for nondestructive testing (NDT). Such designs are outlined. It is noted, however, that the attempt to construct high temperature versions of conventional transducers has led to overcomplicated, expensive structures. In particular, they are modelled on probes used for scanning at ambient temperatures, although scanning is unlikely to be possible at high temperatures. An alternative approach is therefore described, based on the monolithic ultrasonic array structure. This offers not only lower transducer costs, but also full electronic control of the ultrasonic beam angle and emission point, thus facilitating inspection of a region within a test component using only one or two devices in fixed positions. Typical results demonstrating the beam-steering performance of the array, as well as those from B-scan time-of-flight testing, are presented. It is concluded that the problems of transducer development for ultrasonic, high-temperature NDT are not yet completely solved, and that further effort is required in the key areas of materials science and transducer structure. Moreover, a simple design with the minimum of bond lines is most likely to succeed on the grounds of cost and reliability