Single-channel labyrinthine metasurfaces as perfect sound absorbers with tunable bandwidth

Perfect sound absorbers with a deep-subwavelength thickness are important to applications such as noise reduction and sound detection. But their absorption bandwidths are usually narrow and difficult to adjust. A recent solution for this problem relies on multiple-resonator metasurfaces, which are hard to fabricate. Here, we report on the design, fabrication, and characterization of a single-channel labyrinthine metasurface, which allows total sound absorption at resonant frequency when appropriate amounts of porous media (or critical sound losses) are introduced in the channels. The absorption bandwidth can be tuned by changing the cross-sectional areas of channels. A tradeoff is found between the absorption bandwidth and the metasurface thickness. However, large tunability in the relative absorption bandwidth (from 17% to 121%) is still attainable by such metasurfaces with a deep-subwavelength thickness (0.03–0.13λ).