Line Hydrophone with Frequency Dependent Beam Steering

Abstract

A five element line hydrophone will be described in which the acoustic axis of the transducer is steered as a function of frequency. The direction of the hydrophone's maximum response is altered by the introduction of incremental phase shifts in the output voltages of successive motor elements. The phase shifts are introduced through the action of an LC network which produces an approximately linear phase distribution over the length of the line. The slope of the linear phase distribution is a function of the difference between the frequency of the incoming signal and a center frequency which is characteristic of the network. When the incoming signal occurs at the center frequency of the network, no phase increments are introduced and the transducer's characteristics are quite similar to those of a simple line hydrophone. However, in a certain band about the center frequency, the slope of the phase distribution is roughly proportional to the deviation of the signal frequency from the network's center frequency. The hydrophone design was based on a prototype consisting of a multisection, constant k, bandpass network. The hydrophone elements are made up of BaTiO3 and are operated over a frequency band about mechanical resonance. (This work was partially supported by the Bureau of Ships.)