On the use of sympathetic resonators to improve low-frequency underwater transducer performance

Abstract

The achievable gain in the radiation resistance and directivity of a low-frequency underwater transducer due to the presence of an array of sympathetic resonators has been analyzed. The resonators were all taken to be air bubbles, and both the resonators and transducer were taken to be compact (ka << 1). The resonators were taken to be equally spaced around a circle of radius R, with the transducer located on the axis. The gain was calculated for various numbers of resonators as a function of ka(resonator), ka(transducer) and kR, for the transducer in the plane of the resonators and out of the plane a distance of one-quarter wavelength. For the transducer in the plane, a gain in radiation resistance of approximately two is possible with six or more resonators. For the transducer out of the plane, it is shown that a front-to-back discrimination of approximately 8 dB can be achieved, at the expense of a decrease of approximately ten percent in the achievable gain in the radiation resistance, compared to the transducer in the plane of the resonators