Design of a synthetic aperture array to support experiments in active control of scattering

Abstract

A synthetic aperture acoustic array is used to as a spatial filter in a reverberant test facility. The array is used to examine the c' rge in the received signal when a fluid loaded steel plate is replaced by the free surface. Twenty millisecond active pulses at 2 kHz were scattered by the target plate and recorded by the synthetic aperture array for post processing. 'I ie method of reverberant field subtraction was utilized and found unsatisfactory for use with signals of 20 msec duration in a reverberant tank. Array processing using a rectangular amplitude function was marginally successful. A Chebyshev amplitude weighted array was successfully used to demonstrate the ability of a linear array to discriminate between the steel plate and free surface scattering. A computer aided interactive design tool was written to aid in the analysis of array architectures by calculating hydrophone amplitude weights, beamwidth, directivity index and graphically presenting the normalized directional beampattern. The program allows comparative analysis of two array designs simultaneously.