Acoustic Double Zero Index Materials

Wave propagating in a medium with one or more constitutive parameters vanishing does not accumulate any phase retardation and the medium is the so-called zero-index medium. Such a medium is not only mathematically interesting but also bears unusual functionalities, such as wave front engineering, cloaking of objects and wave tunnelling.

In this talk, I will report our recent progress in realizing a two-dimensional double-zero-index materials for air borne sound using space-coiling structures. The space-coiling structure can slow down sound propagation and therefore features an artificial high-refractive index material. A Dirac-like cone is observed at the Brioullin zone center of a periodic array of such structure, indicating the existence of a set of double-zero effective medium parameters. The applications of this double-zero material, including wave front engineering, directional emission, will be demonstrated and discussed.