Temperature-activated coupling effect of nano-Ag coupled ultrasonic transducer during heating process.

High-temperature ultrasonic transducers (HTUTs) are critical for structural health monitoring (SHM). While many existing studies on HTUTs prioritize maximizing operational temperatures or focus on singular high-performance piezoelectric materials or robust bonding techniques like brazing for extreme conditions, this work distinguishes itself by comprehensively investigating a synergistic, multi-component system specifically optimized for stable, well-characterized performance and revealing novel interfacial phenomena within the industrially prevalent 350 °C range. We introduce a HTUT innovatively constructed using a nano-Ag coupling layer, graphite conductive glue for reliable electrical contacts, and mica high-temperature wire. The transducer's performance and underlying mechanisms are systematically assessed from 20 °C to 350 °C. Results demonstrate exceptional high-temperature adaptability with stable echo characteristics. A primary distinguishing contribution is the identification and characterization of a "Temperature-Activated Coupling Effect". Unlike the monotonic performance degradation often anticipated or observed with increasing temperature in many systems, the Temperature-Activated Coupling Effect reveals a unique window where peak-to-peak voltage and SNR are enhanced after surpassing a specific thermal threshold. This phenomenon, attributed to thermally induced improvements at the nano-Ag coupling interface, offers novel insights for optimizing transducer performance. While the mechanical coupling coefficient showed a complex trend, peaking at 100 °C, the overall significance of this study lies in its holistic design approach and the elucidation of the Temperature-Activated Coupling Effect, offering a practical and mechanistically insightful advancement beyond simply achieving temperature tolerance. This provides a distinct pathway for developing HTUTs with tailored performance enhancements for moderately high-temperature SHM applications, contrasting with approaches solely focused on ultimate temperature limits or single-material improvements.