Flexible thin-film ultrasonic transducer development for couplant free high-temperature monitoring

D Irving, H Trodden and D Hughes
Novosound Ltd, Biocity, Bo’ness Road, Newhouse ML1 5UH, Scotland 

While ultrasonic inspection is commonplace in industrial NDT, there are applications that still present significant technological challenges. Ultrasonic measurement capabilities at high temperature, for example, are severely limited. Piezoelectric ceramics used in conventional transducers are restricted by their Curie temperature to applications <200⁰C. Similarly, conventional couplants required for ultrasonic inspection are limited to low-temperature use, while specialist high-temperature couplants offer poor performance. This results in costly, inconvenient workarounds in sectors such as oil & gas and nuclear power, where monitoring of high-temperature assets is desirable.

This paper looks at the use of a novel thin-film piezoelectric material to produce a transducer for high-temperature monitoring. Replacing the conventional ceramic material significantly increases the operating temperatures. In addition, the novel material creates a transducer that is flexible. Flexibility allows the transducer to conform to curved test-pieces such as pipes, negating the need for a couplant. Thickness measurements of a steel pipe were taken over repeated temperature cycles up to 350⁰C. These results demonstrate the durability and long-term reliability of the novel transducer design, highlighting the potential for high-temperature monitoring applications.