Experimental study on concrete microcrack detection efficiency under systematic control of ultrasonic thermal excitation amplitude

Ultrasound infrared thermography has become an effective technique for detecting concrete microcracks. However, the ultrasonic generating circuit system often deviates from its optimal electrical operating state, constraining the thermal excitation efficiency. And previous studies mainly focus on single-parameter control of the efficiency. Accordingly, this study took systematic control of transducer amplitude as the core objective, and designed comparative ultrasonic thermal excitation experiments based on amplitude stability and average amplitude level. The amplitude stability was controlled by adjusting the overall stiffness of the loading device, and the average amplitude level was controlled by adjusting the initial coupling pressure and the operating frequency, thereby altering the system's electrical operating state. On this basis, the response characteristics of thermal excitation efficiency under coordinated parameter control were investigated. The experimental results indicate that, under the experimental conditions, the transducer has a preferred initial coupling pressure and a corresponding preferred operating frequency that differs from its design frequency. By reducing the stiffness of the loading device and matching the preferred initial coupling pressure and preferred operating frequency, both amplitude stability and average amplitude level are systematically optimised. Consequently, the ultrasonic circuit operates in its preferred electrical state and the thermal excitation efficiency is significantly enhanced.