Analysis of acoustic fill time effects on cylindrical arrays

Abstract

When a plane acoustic wave impinges on a cylindrical array, the leading edge insonifics the first few elements of the array. As the wave front continues past the leading edge of the cylinder, more and more elements are insonified until all elements in the array are insonificd. The time between the first and last clement to be insonificd is called array "fill time." For a cylindrical array with a phase-shift beamformer, in which the insonifying pulse length is long compared to the fill time, the resultant beam pattern is essentially the same as a cylindrical array with a delay line beamformer and is approximately the same as a planar array of similar aperture size. Up to this time there has been no detailed description of how the beam pattern is affected when the pulse length and th.c fill time are approximately the same. This article reports a thorough analysis of array fill time of a cylindrical array; a phase-shift beamformer is compared to a delay line beamformer. The conclusion from this study is that fill time has little effect on the array beam pattern as long as the fill time is no greater than the pulse length.