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The construction of piezoelectric polymer film hydrophones has been studied in order to suppress irregularities in hydrophone frequency response and directivity characteristics caused by the formation of induced surface waves on the backing material. A polyvinylidene fluoride (PVDF) hydrophone having a cylindrical baking material rounded at its edge is shown to have flat frequency response in the range of 100 kHz to 10 MHz and to have good directivity in agreement with piston motion theory.

An irregular phenomenon that arises in the directivity characteristics of a hydrophone utilizing a piezoelectric polymer film as an active element is studied. At the radial resonant frequency of a Rayleigh-type surface wave induced on the hydrophone's backing material, a sharp null in the directivity characteristics is observed, as if the hydrophone apparently has a narrow directivity pattern. This irregularity is shown to be caused by the interference between an incident wave and a Rayleigh-type surface wave induced on the backing material.