Applications of Substrate Materials for Interdigital Transducers (IDTs): A Review

Structural health monitoring (SHM) based on ultrasonic-guided waves has been widely investigated for aerospace, transportation, marine engineering, petrochemical equipment and large-scale civil infrastructure. As the core component for guided-wave excitation and signal reception, the transducer directly affects electromechanical conversion efficiency, modal selectivity and service stability. Interdigital transducers (IDTs) are characterized by a lightweight structure, designable wavelength, tunable operating frequency and good array compatibility, and therefore show considerable potential for curved structures, composite components and large-area online monitoring. The periodically repeated interdigital electrode pattern represents a basic form of structural symmetry in IDTs, providing the geometric basis for wavelength matching and frequency-selective response, while substrate properties govern the electromechanical conversion efficiency and stability of the device. This review focuses on the research progress of substrate materials for flexible IDTs. The material characteristics and application status of inorganic piezoelectric materials, piezoelectric polymers, piezoelectric composites and heterogeneous integrated substrates are summarized. The differences among typical substrate systems are compared in terms of electromechanical coupling, flexible conformability, thermal stability, acoustic loss and integration process. Recent applications of IDTs in guided-wave damage detection, flexible sensing, high-temperature monitoring and on-chip acoustic devices are also discussed. The main challenges and future directions of IDT substrate materials are analyzed to provide guidance for material selection, device design and SHM applications.