Broadband extraordinary acoustic transmission via hornlike metamaterials

We demonstrate an extraordinary acoustic transmission through a class of hornlike space-coiling metamaterials, in which the gradual change in channel width ensures such a transmission property in a wide frequency band. This phenomenon is explained in terms of the constitutive parameters based on an effective medium approach, and the underlying mechanism stems from the improved impedance matching and effective near-zero density. Numerical simulations based on finite element analysis are used to verify the effectiveness of our designs, and the results show that this class of metamaterials provides an efficient design methodology for broadband extraordinary acoustic transmission.