STATE SWITCHED TRANSDUCERS - A NEW APPROACH TO HIGH-POWER, LOW-FREQUENCY, UNDERWATER PROJECTORS

In order to produce high-amplitude, low-frequency signals, an underwat er transducer must generate a relatively large volume displacement. Si nce water exerts a large reaction force back on the transducer, ''conv entional wisdom'' dictates that such a transducer would have to be a h igh Q resonant device and thus not be broadband. However, a transducer does not have to be broadband in the conventional sense to meet the r equirements of communication and sonar systems. A transducer that is c apable of instantaneously switching between two discrete frequencies i s adequate for communication and transmission of coded signals; one th at is capable of switching among several frequencies could produce the chirp signals commonly used in active sonars, Ordinarily, a broadband transducer is needed to accomplish the frequency switching rapidly. A way around this difficulty is the ''state-switched'' source concept o riginally proposed by Walter Munk in 1980 which permits instantaneous frequency switching of a high Q resonant transducer while always maint aining the resonance state. The objective of this research has been to investigate this novel approach to the design of high-power, low-freq uency, broadband transducers for use in long-range underwater communic ation, active sonar, and underwater research applications. This paper presents a practical realization of a ''state-switched'' source. (C) 1 998 Acoustical Society of America. [S0001-4966(98)03502-4].