An experimental study of the penetration of a water–sediment interface by a parametric beam

Abstract

A recent theoretical study [D. J. Wingham, J. Acoust. Soc. Am. 76, 1192–1200 (1984)] presented calculations of the farfield secondary pressure in sediment due to a parametric array incident on a water–sediment interface, assuming the array to be completely truncated at the interface. An experimental investigation of this theory is undertaken and the measured secondary pressure contours throughout the sediment are compared with the theoretical estimates. The theory is shown to provide good estimates of the secondary field. The measured secondary pressure variation as a function of beam incidence angle at various ranges is presented and it is apparent that only when the array is truncated in its primary nearfield does the performance of the parametric array differ significantly from a conventional array. It is concluded that the anomalous behavior of parametric arrays, at postcritical angles, relies on virtual sources which are both close to the interface and suitably phased to radiate into the sediment.