A Highly Directional Piezoelectric Shaped Transducer for Frequency-Selective Guided Wave Generation

Ultrasonic guided waves (GWs) are one of the highly promising technologies for structural health monitoring (SHM) due to their capability to travel long distances within a structure with minimal attenuation while effectively interacting with structural defects. Despite this promise, establishing a permanent inspection strategy faces obstacles such as complex circuitry, bulky hardware, and high power consumption. Addressing these challenges, shaped transducers with built-in directional capabilities, such as Frequency-Steerable Acoustic Transducers (FSATs), arise as a promising solution. FSATs take advantage of a spatial filtering effect, allowing wave direction adjustment solely by controlling the actuation frequency, thereby facilitating low-power and rapid beam steering. Nevertheless, previous design strategies have shown some side lobes in their radiation patterns, which may affect angular resolution. This paper introduces a novel shape design approach to enhance FSAT performance, aiming at improving the accuracy of approximating desired directivity functions. The approach integrates Dithering techniques to mitigate side lobes in beam patterns during the quantization process, thus improving the imaging resolution in defect detection applications. Finite Element (FE) simulations were carried out to validate the performance of the transducer design. The proposed transducer was manufactured using the screen-printing technique using silver paste to pattern the shaped electrodes and has potential applications in defect detection in metallic and composite structures.