Ultrasonic Performance of Thin-Film Piezoelectric Transducers and Preload Signal Interpretation Mechanisms in Complex Environments: A Review

Thin-film piezoelectric transducers have attracted wide attention for nondestructive monitoring of bolt preload in complex environments. This is attributed to their compact structure, high sensitivity, and excellent environmental adaptability. This review systematically summarizes recent advances in thin-film piezoelectric transducers under extreme service conditions. It focuses on key material properties, signal response behaviors, and mechanisms for ultrasonic characterization of bolt preload. First, the piezoelectric performance of representative thin-film materials-such as AIN, ZnO, and LiNbO3-is discussed in the context of high temperatures, EMI, and intense vibration environments. Then, the effects of complex environments on the ultrasonic response characteristics of transducers are examined. Special attention is given to signal amplitude variations, propagation time and phase shifts, as well as alterations in frequency and time-frequency features. Finally, the relationship between ultrasonic responses and bolt preload under complex environments is explored. This provides theoretical support and technical guidance for achieving high-precision preload monitoring under extreme conditions.