Parametric investigation of a transducer for guided wave applications

The use of dry-coupled thickness-shear piezoelectric transducers for the generation of ultrasonic guided waves in Non Destructive Testing is well established in industry. The control of guided waves can be supported by designing transducers that achieve a uniform excitation over frequency and contact area. It is necessary to control the wave modes generated such that only modes with characteristics useful for inspection are transmitted and received. Recent research has identified the need to improve the ultrasonic performance in terms of amplitude and signal-to-noise ratio of guided waves via the miniaturization of the transducers. The influence of the geometry of the transducer on the generation of guided waves needs to be investigated. It is well known that the geometry of the transducers influences the normal modes of the ultrasonic transducers, which in turn can influence their ability to excited ultrasonic guided waves. However, the influence of transducer geometry on ultrasonic performance is still not completely understood: mode coupling and the presence of satellite modes might be detrimental for the generation of guided waves. These requirements drive the testing of design changes in terms of geometry and shape of the electrodes to improve the ultrasonic performance of the aforementioned transducers. The transducer is analysed both numerically (by Finite Element Analysis) and experimentally (with Laser Vibrometry) to offer a characterisation of existing piezoelectric elements. It is shown that a change in the actuation area of the transducer leads to a significant difference in the ultrasonic output.