Method of improving the performance of a multimode spherical hydrophone operating near a resonant frequency

A spherical elastic shell surrounded by fluid will be deformed by an imposed acoustic wave. If the shell is made of a piezoelectric material, a voltage is induced by the strains. Elements of shell insulated from one another act as hydophones. The responses of such a shell can be used to determine the direction of an incoming wave. A simple cosine pattern for normal deflection dominates from low frequencies through the resonant frequency for the first mode except for frequency bands near resonance for the third, fifth, and seventh modes. The simple detection of direction is based on a cosine pattern for the induced voltage. It is shown that the surface of the shell can be divided into selected areas which are insulated from one another and such that the sum of voltages from the elements of area is zero for a selected mode. This method is used to remove the effect of the third and most harmful mode and restore the simple cosine voltage pattern in the frequency band near the resonant frequency for the third mode. [Work supported by NAVMAT.]