Numerical study of a near-zero-index acoustic metamaterial

This Letter studies a two-dimensional, membrane-based acoustic metamaterial with a near-zero refractive index. It yields a frequency-dependent effective density that is near-zero at a narrow frequency band centered around its first resonant frequency. This effective density results in its near-zero refractive index. Numerical simulations are shown which demonstrate that the phase in this metamaterial undergoes small changes, and the metamaterial functions as an angular filter such that only a wave with a near-zero incident angle can transmit. Its ability to tailor acoustic phase pattern is also discussed in this Letter. -- Highlights: ► We present a 2D acoustic-metamaterial, which exhibits near-zero-index at a certain frequency band. ► Simulations show that this material behaves as an angular filter. ► Simulations show that this material can tailor acoustic phase pattern.