Acoustic metamaterials

An acoustic metamaterial is a material designed to control, direct, and manipulate sound waves as these might occur in gases, liquids, and solids. The hereditary line into acoustic metamaterials follows from theory and research in negative index material. Furthermore, with acoustic metamaterials controlling sonic waves can now be extended to the negative refraction domain.

Control of the various forms of sound waves is mostly accomplished through the bulk modulus β, mass density ρ, and chirality. The density and bulk modulus are analogies of the electromagnetic parameters, permittivity and permeability in negative index materials. Related to this is the mechanics of wave propagation in a lattice structure. Also materials have mass, and instrinsic degrees of stiffness. Together these form a resonant system, and the mechanical (sonic) resonance may be excited by appropriate sonic frequencies (for example pulses at audio frequencies).

Acoustic metamaterials have developed from the research and results behind metamaterials. The novel material was originally proposed by Victor Veselago in 1967, but not realized until some 33 years later. John Pendry produced the basic elements of metamaterials during the last part of the 1990s. His materials were combined and then negative index materials were realized first in the year 2000 and 2001 which produced a negative refraction thereby broadening possible optical and material responses. Hence, research in acoustic metamaterials has the same goal of broader material response with sound waves.

...
Wikipedia