Investigation of broadband characteristics of PVDF ultrasonic transducers by finite element modeling and experiments

FEM is a powerful tool when used interactively with experiments to deduce the PVDF behavior under various boundary conditions. PVDF is a soft, high damping, and high dielectric loss material whose tensor properties are difficult to measure via standard testing methods. The first part of this paper describes how FEM is used to determine and refine some properties of the PVDF piezoelectric polymer which are unknown or imprecisely provided by the manufacturer. The second part addresses the broadband performance of a PVDF transducer constructed with different layers of PVDF, and different backing configurations in the frequency range from 10 kHz to 850 kHz. Because PVDF can be tailored to special contoured shapes, directivity patterns with low sidelobe level can be achieved which are difficult to obtain with a single ceramic. For example, beam patterns with -30 dB side-lobes have been achieved by canoe shaped transducers via `area shading´. Experimental and predicted curves of transmit sensitivity, receive sensitivity, bandwidth and directivity pattern for PVDF transducers with different backings are shown