Scattering from spheres and cylinders - revisited

Abstract

Backscattering of sound from elastic spheres is commonly applied for calibration of acoustic systems. Measurements on the "form function" of various tungsten carbide spheres turned out not to match simulations based on standard theory and elastic parameters found in the literature. This initiated a search for better parameters. One method for determining the parameters is presented, and the results compared to previously published parameters. It is found that for accurate calibration purposes it is not sufficient to use nominal values for the material, since the actual values may vary from batch to batch and between different manufacturers. Also the suspension method of the spheres turns out to be critical. Measurements on short cylinders of aluminum rotated in the sound beam reveal the presence of two sets of strong lobes in addition to ordinary sidelobes caused by the finite cylinder length. Analysis of these lobes indicates that they are caused by Lamb-type waves excited in the cylinder. Dispersion diagrams obtained from the measurements are presented for the two relevant wave modes.