ULTRASONIC TRANSDUCERS FOR HIGH-TEMPERATURE APPLICATIONS

There is an increasing demand for ultrasonic transducers to work at hi gh temperatures. Transducers operating in the range from 400 to 1000 d egrees C are being applied in the power, process, automotive and aeroe ngine industries, as well as in materials research. To date, the major ity of high temperature transducer designs have been based on adaptati ons of conventional single and dual-element probes for nondestructive testing (NDT). Such designs are outlined. It is noted, however, that t he attempt to construct high temperature versions of conventional tran sducers has led 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 cost s, but also full electronic control of the ultrasonic beam angle and e mission point, thus facilitating inspection of a region within a test component using only one or two devices in fixed positions. Typical re sults demonstrating the beam-steering performance of the array, as wel l as those from B-scan time-of-flight testing, are presented. It is co ncluded that the problems of transducer development for ultrasonic, hi gh-temperature NDT are not yet completely solved, and that further eff ort is required in the key areas of materials science and transducer s tructure. Moreover, a simple design with the minimum of bond lines is most likely to succeed on the grounds of cost and reliability.