Acoustic scattering by smooth and rough elastic cylinders insonified by directional sonars

Abstract

Realistic sonars radiate spherically spreading waves and have directivity. Therefore, they insonify a target over a finite number of Fresnel zones and span a continuum of oblique incident angles, even when the center of the beam is at normal incidence. These effects strongly influence both the overall scattered pressure levels and resonances. For example, because of the spreading of the beam and associated oblique insonification within the beam, axially propagating guided waves are generated that would not have otherwise existed for an idealized incident plane wave. This investigation illustrates practical sonar properties and their effects on cylinder scattering both theoretically and experimentally. An approximate theoretical formulation for acoustic scattering by elastic cylinders is proposed in the form of a simple line integral accounting for these properties. Laboratory measurements are also presented to test the range of validity of the formulation for smooth cylinders under both monostatic and bistatic configurations. This study is further extended for the case of rough elastic cylinders.