2. Metamaterials and applications

2.1 Acoustics

A body of work carried out since 2000 has provided a definition and the main characteristics of an acoustic metamaterial. It is an artificial composite structure designed to have negative effective density and/or negative effective compressibility in a given acoustic frequency range. It is manufactured by inserting into a "3D" solid or liquid matrix, or into a "2D" plate, mechanical resonators with characteristic sizes much smaller, in the frequency range under consideration, than the wavelength of the elastic waves propagating in the matrix. This results in a homogenizable composite material described by effective quantities. Although periodicity is not a necessary condition, resonators are generally organized periodically. The dispersion curves then show flat bands...