STUDY OF SURFACE ELASTIC-WAVE INDUCED ON BACKING MATERIAL AND DIFFRACTED-FIELD OF A PIEZOELECTRIC POLYMER FILM HYDROPHONE

A distinctive irregularity in the frequency response of a piezoelectric polymer film hydrophone, which is not predicted by the use of conventional theory, has been observed. It was confirmed in a previous study [Y. Nakamura and T. Otani, Jpn. J. Appl. Phys. Suppl. 31-1 31, 266-268 ( 1992) ] that the irregularity can be attributed to the radial resonance of a surface wave induced by the incident pressure on the hydrophone's backing material. To estimate theoretically the frequency response of the hydrophone, the transient acoustic field on the receiving surface of the hydrophone was studied by time-domain analysis. The field is theoretically described in the time domain as the superposition of an incident wave, a reflected plane wave, a diffracted edge wave, and a leaky elastic wave that originates from a surface wave propagating along the radius on the hydrophone's backing material. The validity of the theoretical analysis of the acoustic field on receiving surface is verified by experimental observations. Thus it is shown that the frequency response of the piezoelectric polymer film hydrophone is estimated from the analytical results of the acoustic field.