Parametric acoustic source beamwidth control

In addition to its narrow beamwidth and wide-band 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 an adjustable beamwidth is required. This article 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.