[135] Flexible ultrasonic transducer development for couplant-free high-temperature monitoring

While ultrasonic inspection is commonplace in industrial non-destructive testing (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 <200°C. 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, including 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 low-profile and flexible. Flexibility allows the transducer to conform to curved test-pieces such as pipes, negating the need for a couplant. The low profile makes the transducer ideally suited to permanently installed monitoring applications. Thickness measurements taken of a steel pipe over repeated temperature cycles at 250°C showed no significant change in transducer output. This demonstrates the durability and long-term reliability of the transducer, highlighting the potential for high-temperature monitoring applications.