9. Acoustic Cloaking via Homogenization

Acoustic cloaking is the mechanism representing the ideal acoustic stealth. We introduce and discuss the acoustic cloak, a material shell that renders an object acoustically ‘invisible’ thanks to its presence surrounding the object. It has been shown that cloaking shells require very complex parameters to be realized. This complexity comes from the fact that their acoustic parameters must be anisotropic, inhomogeneous and divergent near the cloaked object. This chapter explains how to engineer artificial structures, which have been called acoustic metamaterials or metafluids, that respond dynamically as anisotropic and inhomogeneous materials. The metafluids are made from arrays of isotropic and homogeneous elastic cylinders or by metallic plates cylindrically corrugated. We also propose solutions to remove the divergences appearing in the design of cloaking shells. It is therefore predicted that, although difficult to realize, cloaking shells are not impossible by using metafluids based on the homogenization of periodic structures.