Specialized drive waveforms for the parametric acoustic source

In addition to its narrow beamwidth and wideband capability, the underwater parametric acoustic source has the advantage of maintaining a relatively constant beamwidth over a wide range of difference frequencies. However, for some applications the beamwidth of the difference frequency is narrower than desired or adjustable beamwidth is required. This paper describes techniques by which the beamwidth at a given difference frequency can be increased and varied over a 3 to 1 range by controlling the input waveform and amplitude to the transducer. The effect of the waveform changes on the harmonic content of the difference frequency energy is also discussed. The relatively low efficiency of the source prompts investigation of methods to increase overall efficiency. Techniques to improve efficiency through the use of waveforms suitable for switching drivers are described and supported by experiment.