Design and application of an underwater acoustic parametric source

Abstract

Parametric sound generation has been an active area of applied research for the last ten years. The acoustic parametric source takes advantage of the non-linearity of the medium to generate energy at the difference of two high frequencies. The principal advantage of a parametric source over a conventional transducer is its high resolution capability. The characteristic is a result of its narrow beam width (with no attendant side lobes) and broad bandwidth. The parametric source was designed and tested in the laboratory and also at sea. Laboratory studies showed severe broadening of the parametric beam and reduction of difference-tone pressure on reflection from a smooth air-water surface. This is attributed to the phase reversal that occurs on reflection. The coefficient of amplitude variation at sea was found to be less than 31 at the depth of 20 and 40 ft. and was much higher at 10 ft. depth. The coefficient of amplitude variation was higher for the parametric beam as compared to that of a conventional sound beam at the depths of 20 and 40 ft. The parametric beam had lower coefficient of variation as compared to that of a conventional beam at the depth of 10 ft.