Acoustic metamaterials based on phononic crystals.

Abstract

This talk will review recent results on the topic of sound propagation through periodic arrays of sonic scatterers embedded in a fluid or a gas. These structures, which are called phononic crystals, define in the homogenization limit (i.e., for lattice separations much lower than the sound wavelength) a class of acoustic metamaterials with extraordinary properties. For example, they are solid structures that are used to engineer effective fluid-like systems with anisotropic dynamical mass density, a property that can be tailored by changing the parameters of the structure and the material composition of scatterers. A homogenization method based on multiple scattering theory has been developed and semianalytical expressions for the effective acoustic parameters will be given. By using these expressions it is easy to design novel refractive devices like gradient index sonic lens with a perfect match of impedance with the background. Results for a gradient index lens made of aluminum cylinders in air will be presented. Moreover, metamaterials with mass anisotropic have also been proposed to build broadband acoustic cloaks and a new type of crystals named radial sonic crystals, which are radially periodic structures that verify the Bloch theorem. [Work supported by ONR and by MICIIN of Spain.]