0.36BiScO3-0.64PbTiO3/Epoxy 1-3-2 High- Temperature Composite Ultrasonic Transducer for Nondestructive 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 0.36BiScO3-0.64PbTiO3 (BSPT), which is preferred piezoelectric materials at $200~^{\circ }$ C– $300~^{\circ }$ C, and high-temperature epoxy with a center frequency of 6 MHz were designed and fabricated. From $25~^{\circ }$ C to $250~^{\circ }$ C, 1-3-2 composites show a higher electromechanical coupling coefficient ${k}_{t}$ especially at high temperatures (~0.53 at $25~^{\circ }$ C and ~0.64 at $250~^{\circ }$ C) than monolithic BSPT (~0.5). The signal of the pulse-echo response of 1-3-2 HTCUTs is distinguishable up to $250~^{\circ }$ C and remains stable ( ${V}_{\text {pp}}~\sim 500$ mV) below $150~^{\circ }$ 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 (~103% at $250~^{\circ }$ C) compared with that of monolithic BSPT HTUTs (~30% at $250~^{\circ }$ C). To verify the excellent performance, B-mode scanning imaging measurement of a stepped steel block and defect location detection of a steel block was performed, showing the potential for high-temperature NDT applications.