Interaction of sound waves with submerged shells that have internally mounted masses

We study the scattering of sound waves by a spherical steel shell in water that has a pair of heavy masses internally mounted by springs and is neutrally buoyant. The pair of hanging masses change the backscattering cross section (BSCS) of the (empty) shell. If the compliance of the mounts is varied, that also changes the BSCS of the shell. The distorting effect is strongest when the incident wave hits the shell at the point of attachment of the masses. The distortion consists of a set of amplitude modulated resonance features concentrated within a relatively narrow frequency band containing the main resonances of the coupled oscillator formed by the mounted masses