Nearfield of a large acoustic transducer, Part II: Parametric radiation

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Abstract
The transducer is the same as the one considered in an accompanying paper by the same authors [Part I, J. Acoust. Soc. Am. 7 2, 1056–1061 (1982)]. It has a diameter of 182 cm, and is composed of 364 elements, 4.8×6.4 cm each, which are distributed in 13 equally spaced rings. It is used to generate difference frequency sound at 0.5–5 kHz in water. Amplitude and phase of the generatedsound are measured at various distances in the nearfield of the transducer. The results are compared with calculations based on the quasilinear approximation of the governing equations. Simplifications are obtained by utilizing the parabolic approximations [J. Naze Tjo/tta and S. Tjo/tta, J. Acoust. Soc. Am. 6 7, 484–490 (1980)]. This also makes it possible to use a realistic model for the primaries (see the accompanying paper) when evaluating the nonlinear source term, such that all effects of the nearfield oscillations in amplitude and phase are fully accounted for. The analytical results obtained also apply to the case of an amplitude and/or phase shaded source.

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