Acoustic Scattering from a Strained Region

Acoustic coatings for underwater applications may be made of a composite material consisting of gas-filled microspheres embedded in a rubber-like material. Under typical applied hydrostatic pressure the microspheres are compressed to a large static deformation. The region of the rubber around each microsphere is therefore also subject to large deformation. The Study Group addressed the problem of the propagation of small amplitude acoustic waves through this pre-strained region around the microsphere. The report reviews the material models, and formulates the full scattering problem. It is also shown how the monopole scattering strength of the microsphere embedded in the pre-strained material can be calculated by using the dynamic shear modulus of the material and the solution to the static compression problem.