Modelling the beam pattern of piezopolymer interdigital transducers (IDT) for optimizing the off-axis response

Interdigital Transducers fabricated by piezopolymer (PVDF) film have been studied and applied for active monitoring of damages in Structural Health Monitoring systems. The generated ultrasonic guided waves can be selected according to the dimensions of electrodes pattern. In a previous work was observed experimentally by a Laser Doppler Vibrometer that the beam pattern was different from the expected one based on a comb type configuration. This work has investigated this important characteristic of piezopolymer IDTs by a 3D FEM analysis. It was found the influence of the finite dimensions of the two bus bars in the electrodes pattern that are necessary for the electrical connections. The simulation results and the experimental validation have confirmed the presence of the off -axis response. This characteristic can be exploited for optimizing the IDT design and the placement of IDTs on the monitored structure.