Electromagnetic sonar transmitter apparatus and method utilizing offset frequency drive

A sonar transmitter includes a source means for providing an actuation signal to drive an electromagnetic transducer projector without the use of bias magnetization. The invention utilizes an offset actuation frequency technique in which electrical driving signals are applied which have a frequency or frequencies other than the desired frequency of the acoustic signal projected into a liquid medium. In presently preferred embodiments, one or two driving signals may be utilized. If one driving signal is utilized, the acoustic signal will be at twice the driving signal frequency. If two driving signals are utilized, the acoustic signal will be at the sum or difference frequency of the driving signal frequency. The actuation signal is applied to coils of the transducer's electromagnets to produce an electromagnetic attractive force having a significant component at the desired frequency of the acoustic signal. The force component urges movement of the electromagnets, causing a radiating surface of the transducer to elastically flex, thereby producing the acoustic signal.