A broadband acoustic omnidirectional absorber comprising positive-index materials

We propose a broadband acoustic omnidirectional absorber (AOA) made of acoustic metamaterials having a positive index, which guides an incident acoustic wave into a central cavity spirally without backscattering. Numerical simulations show that the AOA has an absorption cross section remarkably larger than its cavity within a broad band, which is of potential practical significance to various applications such as sound absorption and noise control. A possible scheme for the practical realization of the AOA is also briefly discussed.