Enhanced directional acoustic emission based on anisotropic metamaterials

The emergency of anisotropic acoustic metamaterials provides great opportunity for controlling acoustic propagations and realizes many exotic acoustic phenomena. However, the realization of enhanced directional propagation with an unchanged wavefront based on anisotropic metamaterials remains a challenge. Here, we report both experimentally and numerically that an enhanced directional acoustic emission is realized by a broadband anisotropic metamaterial consisting of an array of units constructed by a square cavity and two symmetric straight channels. The anisotropic property of the metamaterial exists in the range of 8430-9460 Hz, which arises from different effective impedances in the orthogonal directions. Based on the anisotropic property, we realize an enhanced directional acoustic emission with an unchanged wavefront by placing a cylindrical source at the center of the metamaterial, in which the enhanced emission in the y direction is attributed to the prohibition of acoustic propagation in the vertical direction induced by mismatched impedance. Besides, the influences of air attenuation on the enhanced directional emission are discussed in detail. More interestingly, we also realize the enhanced directional acoustic emission for two cylindrical sources in the anisotropic metamaterial. The proposed acoustic metamaterial has the advantages of broad bandwidth, high anisotropy, enhanced directivity, and unchanged wavefront, showing promising applications in acoustic communication and architectural acoustics. Published under license by AIP Publishing.