Analysis of the Frequency Response of Simple Geometric Targets

Abstract

Measurements of pulse-echo forms and steady-state frequency response of air- and water-filled aluminum spheres and cylinders in water are presented. These compare favorably with theoretical results. The nondimensional frequency (ka) range is 24≦ka≦60. Scattering paths defined by the cross-sectional geometry of the targets are identified, and it is shown that it is constructive and destructive interference between the energy returned along the different scattering paths that generates the frequency response of the target as frequency is changed. Similarities in the backscattered echoes from spheres and cylinders at normal incidence due to similarities in the scattering geometry are described. Measurements of circumferential waves in spherical shells, believed to be the first reported for this target form, are presented.