Design and demonstration of acoustic bends with metamaterials

In this paper, we propose the design of broadband acoustic bends in air. A bending structure composed of perforated panels with various hole-sizes is firstly realized and experimentally demonstrated in a 2D waveguide. However, the perforated plates only tune the refractive index of the unit cell, resulting in impedance mismatch between the structure and the air. Then, we introduce side pipes with various volumes to adjust the impedance of the acoustic bend. Both the simulated and experimental results verify that the acoustic beam can be rotated smoothly through these bends in a wide frequency range. In addition, the transmission intensity is higher than 90% after improving the impedance of the bend. The good performance of these acoustic bends shows their potential applications in many fields, like detection and absorption in pipelines.