Acoustic metamaterials are artificial materials whose acoustic properties are adjusted to produce the peculiar wave phenomena. The materials are featured by a miniature unit structure whose size is usually smaller than the wavelength. The apparent physical properties are determined according to the structural arrangement rather than material property itself. In this study, we propose the metamaterial structures by which the transmitting acoustic waves deflect with a predesigned angle. Two structures were investigated: the one with a series of columnar obstacles arranged side by side whose diameters were varied unidirectionally, and the other composed of a series of acoustic ducts where each set of neighbouring paths had a constant relative length. Numerical simulations showed that the incident wave deflected exactly as designed to the target deviation angle in both structures. The measured sound field for the latter structure also showed that the sound with frequency from 500 Hz to 4kHz could be deflected at the angle of 45 degrees.

Sound wave; Acoustic metamaterial; Deflection; Path difference; Finite element analysis