State switched acoustic source

Abstract

To produce high amplitude low-frequency signals, an underwater transducer must generate a relatively large volume displacement. Since water exerts a large reaction force back on the transducer, ‘‘conventional wisdom’’ dictates that such a transducer would have to be a high Q resonant device and thus not be broadband as seemingly required for many applications. However, a transducer does not have to be broadband in the conventional sense to work in communication and SONAR systems. A transducer capable of switching between two discrete frequencies is adequate for communication and one capable of switching among several frequencies could produce chirp signals for active sonars. Ordinarily, a broadband transducer is needed to switch frequencies rapidly. It is theoretically possible, however, to instantaneously switch frequencies with a high Q resonant system provided that the system’s resonant and drive frequencies are altered simultaneously. Such a ‘‘state-switched’’ transducer [Munk, Webb, Birdsall, unpublished (1980), (1981)] would retain the advantages (high power, high efficiency, and large displacements) of a high Q resonant transducer without the accompanying disadvantage of slow response time. A state-switched acoustic source with an active spring of PZT has been built to demonstrate the state switching concept. [Research supported by ONR 334.]