Analytical Approximations for Sub Wavelength Sound Absorption by Porous Layers with Labyrinthine Slit Perforations

Analytical approximations for the acoustical properties of a rigid-porous matrix perforated by labyrinthine slits are developed using classical theories sound propagation in tortuous and absorption double porosity materials. Predictions enhanced low-frequency result from combination pressure diffusion labyrinth tortuosity if there is high permeability contrast between slit. Additional insight into predicted influence porous gained considering to be provided inclined micro-slits. Extra can introduced alternating width An alternating-width vertical-wall perforation lead peaks relatively low-flow-resistivity low-porosity matrix. Example predictions, even when underestimates tortuosity, demonstrate potential slit perforations achieving narrowband deep sub wavelength thin hard-backed layers.