LAUSR

By utilizing a unit cell helical hole acoustic metamaterial, we illustrate the realization of broadband transmission without the need for the interlayer spacing or gradient structure. Its transmission property is evaluated analytically and numerically based on effective medium approximation theory, and its effective material properties are extracted. By modifying the structure, a broadband transmission is obtained as a result of constructive interference of waves due to the coupled helices along with Fabry–Perot resonance. Therefore, the bandwidth is improved from 36% to 82%. Furthermore, we experimentally verified the acoustic transmission property of the modified and unmodified structures, and good agreement is achieved with numerical simulation. Compared to a double-layer modified metamaterial, a single layer shows a greater bandwidth. Therefore, the proposed metamaterial could open up to a compact and broadband impedance matching metamaterial for a wide range of applications.