Characteristics Of Acoustic Metamaterials

Acoustic metamaterials refer to the artificial materials, which are usually composed by periodical unit cell in the sub-wavelength scale, with unique properties that do not exist in nature, providing new ways to design acoustic devices. In this paper, we investigate the design of acoustic meta-atom and some typical meta-devices, with the main contents of this paper listed below:(1) A two-dimensional acoustic lens with gradient refractive index is designed based on acoustic metamaterials, which is based on identical elements with various dimensions. This lens is made of photopolymer through rapid prototyping stereo lithography. Compared with traditional acoustic lens, it has a number of advantages including smaller size, higher accuracy, lighter weight and easier implementation.(2) A two-dimensional acoustic spatial power combination device is designed based on anisotropic zero-index acoustic metamaterial. Omnidirectional radiation can be realized at the presence of the device, resulting in efficient combination of spatial power from all acoustic sources. Both the numerical and experimental results agree very well. The proposed idea can be extended to three-dimensional case to generate perfectly coherent isotropic radiation.(3) An acoustic low-scattering coding metasurface is designed based on randomly-distributed 3-bit coding elements. Due to the diffusion effect invoked by the metasurface, the backscattering of incident waves can be greatly reduced in a wide frequency range, which may find potential applications in the stealth technologies.