Ultrasonic thin film transducers for high-temperature NDT

Ultrasonic thin films have advantages over conventional transducers for non-destructive testing, especially at high temperatures. We have demonstrated thin film ultrasonic devices in operation at temperatures over 400°C. Pulse-echo and through-transmission modes have been used, with standard ultrasonic pulser-receivers. The films are deposited directly onto the test components, thus eliminating problems with acoustic coupling at high temperatures. Transducers formed in this way are low-profile, unlike water-cooled transducers or those requiring thermal isolation via buffer rods. It is possible to deposit the films onto curved surfaces and extensive surface preparation is not required. Pulse-echo tests have been carried out on aluminium and mild steel components, showing that back-wall echoes and simulated defects can be detected through several centimetres of material. There are clearly important potential applications in non-destructive testing at high temperatures including detection of defects in hot components and monitoring pipewall thickness in high-temperature plant.