Characterisation of the vibration of an ultrasonic transducer for guided wave applications

Dry-coupled thickness-shear piezoelectric transducers are typically used to excite guided waves in plate-like or tubular structures in the frequency range of 20-150 kHz. The dispersive behaviour of guided waves and the excitation of unwanted wave modes require a precise tuning of the excitation frequency to facilitate effective inspection. A natural frequency analysis of a typical piezoelectric transducer has been performed to identify the shape of vibration in the frequency range indicated. Moreover, an experimental analysis of the vibration of the piezoelectric element through a scanning laser Doppler Vibrometer has been conducted. The numerical and experimental results agree in indicating no longitudinal mode is present up to 94 kHz. Experiments also has shown that the higher the frequency the higher the longitudinal component of displacement.