Broadband unidirectional and omnidirectional bidirectional acoustic insulation through an open window structure with a metasurface of ultrathin hooklike meta-atoms

We report the theoretical and experimental realization of an open window structure which exhibits the unusual properties of broadband unidirectional and omnidirectional bidirectional acoustic insulation. The open window is constructed by separate blades attached with metasurfaces of ultrathin hooklike meta-atoms which can change the lateral momentum of acoustic waves. Such a manipulation of momentum leads to an acoustic blind region and enables broadband unidirectional acoustic transmission. By improving the phase distribution of the metasurfaces, the fractional bandwidth can reach about 0.36. Interestingly, by mechanically rotating the blades to oblique positions, the unidirectional acoustic transmission can be conveniently converted into omnidirectional bidirectional acoustic insulation. The proposed metasurfaces composed of the hooklike meta-atoms have the advantages of broad bandwidth, ultrathin thickness (about λ/12), and easy fabrication. Our work opens up an approach for advanced acoustic manipulation in tunnels and windows, which has great potential in applications such as noise control and architectural acoustics.