three-phase phononic materials

We consider a strongly heterogeneous material consisting of three phases: an elastic matrix, medium-size inclusions periodically embedded in the elastic matrix; these inclusions are constituted by small rigid inclusions coated by a very compliant material. The dependence on scale of elasticity coefficients of the deformable medium-size inclusions is treated in the context of linear elasticity by the homogenization procedure providing a limit model that inherently describes band gaps in acoustic wave propagation. The band gaps occur for certain intervals of long wavelengths for which a frequency-dependent "mass density" tensor is negative. We illustrate the theoretical results with numerical simulations.