Acoustic scattering of fluid-filled spheres: Modeled and experimental results

Abstract

Investigation into the scattering nature of surfaces or other physical objects often requires the use of measurement systems which cannot always be well controlled. This lack of control can be compensated for by calibrating the resulting measurements against a known target. While these targets can be any object, the goal is to use a target that has a stable scattering response and is independent of angle. The ideal shape is that of a sphere but even this can be improved with the addition of internal fluids that focus and temperature stabilize the scattering response. A scatter response model of a sphere has been developed and used to design four thin-walled spheres, each with a different diameter and filled with a focusing fill fluid (Fluorolube). One pair of spheres was measured in an ocean environment while the second pair was tested in a controlled test tank from 5–120 kHz but using shorter continuous wave pulses. While the ocean-measured spheres closely matched the model, the test tank measurements provided insight to the model’s near-field limitation and low-frequency noncontinuous wave effects.