Ventilating noise barrier with slow wave propagation metamaterial

There has been rapid development of acoustic metamaterials over the past decades, which provide more flexible and effective alternatives to conventional acoustic applications in the field of noise insulation. Recent approaches resolve the conflict between noise insulation and ventilation with partially open meta-structures. Such a binary design eliminates the monopolar and dipolar modes, leading to a total reflection boundary. It holds huge potential in practical scenarios. More simple structures and a broader operating bandwidth are highly desirable to enhance its applicability. This work adopts a binary structure to tune the surface response: open areas with air and slow wave propagation layers with helical-structured metamaterial. These two phases alternate along the radial direction, forming a concentrically layered ventilating insulator. The numerically optimized metamaterial performs efficiently in a wide frequency band and has been validated through experiments.