Acoustic scattering by elastic cylinders: Practical sonar effects

Abstract

Acoustic scattering from elastic cylinders has been studied extensively over the last few decades. However, the vast majority of theoretical investigations have focused on idealized plane wave, point receiver solutions, ignoring realistic sonar effects. Acoustic transducers are characterized by spherically spreading waves and often have transmit and receive beams that are directional. Because of the spreading, even during broadside measurements, these sonars excite cylinders obliquely. This investigation involves acoustic scattering by spot-insonified infinitely long elastic cylinders, and studies effects caused by practical sonar constraints both theoretically and experimentally. Calibrated broadside measurements of backscattering are presented for various cylinder and source/receiver geometries including both monostatic and near-monostatic configurations. In all measurements, the ratio of the footprint length of the target relative to the first Fresnel zone diameter is chosen such that the entire first Fresnel zone dominates the scattering. This ensures that the scattering from the cylinder spreads cylindrically and hence the cylinder behaves like an infinite target. A theoretical formulation is developed to account for beam spreading and directivity of practical echo-sounders. Comparisons between theoretical predictions and experimental data are presented. [Work funded by ARPA-E.]