Experimental realization of broadband acoustic omnidirectional absorber by homogeneous anisotropic metamaterials

We design a two-dimensional broadband acoustic omnidirectional absorber (AOA) simply comprising homogeneous anisotropic metamaterials to enlarge the absorption cross-section of a smaller core with matched acoustic impedance as the previous AOAs do, which generally involve complicated design of gradient-index or negative-index materials. Furthermore, AOAs with asymmetric/large geometrics can be realized conveniently, which will otherwise require a complex redesign of parameters. The proposed scheme is also extendable to three-dimensional cases. An implementation using angularly distributed fins was demonstrated experimentally, showing the broadband functionality of the designed absorber. Such metamaterial-based acoustic absorbers may have potential applications in various fields such as acoustic energy concentration, noise control, etc.