0.36BiScO₃-0.64PbTiO₃/Epoxy 1-3-2 High-Temperature Composite Ultrasonic Transducer for Non-destructive Testing Applications

The development of high-temperature nondestructive testing (NDT) requires ultrasonic transducers with good temperature resistance and high sensitivity for improved detection efficiency. Piezoelectric composite can improve the performance of transducers because of its high electromechanical coupling coefficient and adjustable acoustic impedance. In this study, 1-3-2 composites and 1-3-2 high-temperature composite ultrasonic transducers (HTCUTs) based on 0.36BiScO ₃ -0.64PbTiO ₃ (BSPT), which are preferred piezoelectric materials at 200°C-300°C, and high-temperature epoxy with a center frequency of 6 MHz were designed and fabricated. From 25°C to 250°C, 1-3-2 composites show a higher electromechanical coupling coefficient k_t especially at high temperatures (~0.53 at 25°C, and ~0.64 at 250°C) than monolithic BSPT (~0.5). The signal of the pulse-echo response of 1-3-2 HTCUTs is distinguishable up to 250 °C and remains stable ( V_pp ~500 mV) below 150°C, exhibiting higher sensitivity (improved by 7 dB) than that of monolithic BSPT high-temperature ultrasonic transducers (HTUTs). Bandwidth has been greatly enhanced especially at high temperatures (~103250°C) compared with that of monolithic BSPT HTUTs(~30250°C). To verify the excellent performance, B-mode scanning imaging measurement of a stepped steel block and defect location detection of a steel block were performed, showing the potential for high-temperature NDT applications.