Ultra-compact canvas-type acoustic metasurfaces for uniform sound field in indoor environments

This study proposes an ultra-compact canvas-type metasurface engineered with complex-valued impedance to enhance sound field uniformity in indoor environments such as home theaters and recording studios. The metasurface consists of sub-wavelength Helmholtz resonators and is visually integrated with printed artwork, enabling seamless deployment in interior spaces. A systematic two-stage design framework based on full-wave finite element analysis is developed to account for low-frequency wave phenomena-including diffraction and scattering, and thermo-viscous dissipation in the narrow-neck orifices. By strategically adjusting complex impedance of the metasurface, the spatial standard deviation of sound pressure level (SPL) is reduced by up to 77% at the target frequency of 115 Hz within the designated listener region. Compared to traditional absorptive wall treatments, the metasurface achieves superior uniformity while using only 1/85 of the material volume. To broaden the operational bandwidth, three metasurfaces targeting multiple frequencies of 100, 115, and 127 Hz are designed with their installation locations and impedances optimized for each frequency. This approach improves SPL uniformity at discrete frequencies as well as across a wider frequency range, enhancing spectral flatness. These results demonstrate the potential of aesthetic acoustic metasurfaces as space-efficient and visually unobtrusive solutions for low-frequency sound field control in indoor environments.