Influence mechanism of loading devices on transducer excitation effects in ultrasound-excited thermography

Ultrasound-excited thermography technology has proven effective in detecting microcracks as small as 0.01 mm in concrete specimens; however, its range of detection distance is limited. Coupling pressure is essential for ultrasonic excitation, but conventional loading devices introduce excitation disturbance force when applying this pressure, affecting the thermal excitation effects. In this study, the thermal excitation effects on microcracks were investigated based on the experimental results from the ultrasonic excitation system, with the analysis incorporating the impacts of transducer resonance frequency shifts caused by coupling pressure variations. The excitation state of the transducer’s vibrating surface was also explored based on simulation results of vibration disturbances from the loading device, which was verified by the experimental results, thus the influence mechanism of the loading device on the transducer excitation effects was elaborated. Results show vibration pattern of transducer excitation surface amplifies coupling pressure disturbances of loading devices. Load impedance of transducers undergoes significant variations under force disturbances, leading to reduced ultrasonic energy output of transducers and consequently deviating from target thermal excitation effects. Future work can focus on modifying the supporting column material of loading devices to optimise the stiffness and minimise the additional force disturbances from loading devices during transducer excitation.