Thermoviscous effects on sound transmission through a metasurface of hybrid resonances

This letter analytically and numerically examines sound transmission through a metasurface of hybrid resonances in the presence of thermoviscous dissipation. The metasurface unit of a subwavelength thickness consists of a slit and series of sided resonators embedded in air. Both wall friction and thermoviscous diffusivity in the unit are taken into account. The results reveal that the dissipation has a weak influence on phases even when there is a large loss. The dissipation reduces the transmission by 28% when the thermoviscous boundary layer thickness is only around 2.3% of the slit width. Optimal designs for minimal dissipation are addressed.