Effect of Elastic Coating on the Sensitivity of Polyvinylidene Fluoride Film Using a Finite-Element Approach

The effect of a coating on the sensitivity of polyvinylidene fluoride (PVDF) is investigated in this study and the underlying physical mechanisms are explained. The spectral and directional sensitivity of a coated PVDF film are significantly different from that of an uncoated PVDF film, and this can be explained by the amplification of the in-plane stress component by the transmitted shear stress at the PVDF–coating interface. The amplification is dependent on the elastic property and thickness of the coating material. The sensitivity of the coated PVDF film below the first resonance frequency, owing to the destructive superposition of in-plane and normal voltage components, can be increased by adding a thick and soft coating or a thin and stiff coating. A thick and soft coating significantly amplifies the in-plane voltage component and makes it dominant, while a thin and stiff coating reduces the in-plane voltage component and hence the normal voltage component becomes dominant. The directivity sensitivity of the film at low frequency is also explained by the angular dependence of the PVDF–coating interaction. The demonstrated effect of the coating material on the spectral and directional sensitivity of PVDF helps in understanding the measured results of existing PVDF hydrophones, and in designing PVDF-based hydrophones and acoustical intensity probes with a desired response.