Appearance of elastic wave contributions in high resolution acoustic images

Abstract

Studies involving plane wave scattering by finite cylindrical shells at oblique incidence display monostatic echo contributions from surface elastic waves. These waves follow helical paths along the shell’s surface and are guided back in the source direction after reflection from the cylinder truncation [X.‐L. Bao, 1461–1465 (1993)]. The present research examines such effects viewed in the time record of a high resolution sonar system. The target consists of a finite cylindrical shell with a radius to thickness ratio of 5%. The shell is immersed in water and is subject to both exterior and interior fluid loading. It is ensonified with short tone bursts of narrow beam width over a range of incidence angles 90≥φ≥50, where φ is measured relative to the cylinder axis. The backscattered echo signature exhibits prominent artifacts as a result of scattering processes involving the s0 and a0 Lamb waves interacting with the cylinder truncation. The echo contributions are extremely sensitive to the angle of inciden...