Abstract: A method for reducing cavitation around underwater acoustic projectors is described. The projector is cleaned with a surfactant and then encapsulated with an aqueous gel containing a polysaccharide polymer such as a chitosan derivative, a hydrophilic stabilizer and a biocide.

Abstract: A piezoelectrically-driven, resonant-pipe projector has formed therein vents to broaden the response of certain cavities resonances and to increase the response between these resonances. The projector exhibits a relatively high electroacoustical efficiency, is capable of medium to high power output over the operating band, and is not depth dependent or depth limited.

Abstract: A hydrophone which provides for cancellation of signals caused by acceleration forces and variations in water pressure head. The structure is comprised of a transducer for sensing an acoustic pressure wave as well as an acceleration force, and an accelerometer, which is isolated from the acoustic pressure wave, for sensing only the acceleration force. The transducer and the accelerometer are connected so as to subtract the acceleration output. Only the acoustic pressure wave output signal remains. Circuitry is also provided for cancelling the pressure head signal.