Using simple shape three-dimensional rigid inclusions to enhance porous layer absorption

Abstract

Backed Porous layer with inclusions 1 AbstractThe absorption properties of a metaporous material made of nonresonant simple shape three-dimensional inclusions (cube, cylinder, sphere, cone and torus) embedded in a rigidly backed rigid frame porous material is studied. A nearly total absorption can be obtained for a frequency lower than the quarter-wavelength resonance frequency due to the excitation of a trapped mode. To be correctly excited, this mode requires a filling fraction larger in the three-dimensions than in the two-dimensions for purely convex (cube, cylinder, sphere, and cone) shapes. At low frequencies, a cube is found to be the best purely convex inclusion shape to embed in a cubic unit cell, while the embedment of a sphere or a cone cannot lead to an optimal absorption for some porous materials. At fixed position of purely convex shape inclusion barycentre, the absorption coefficient only depends on and filling fraction and does not depend on the shape below the Bragg frequency arising from the interaction between the inclusion and its image with respect to the rigid backing. The influence of the angle of incidence is also shown. The results, in particular the excitation of the trapped mode, are validated experimentally in case of cubic inclusions.

Enhancing the absorption properties of acoustic porous plates by periodically embedding Helmholtz resonators

“…The analysis is performed in the viscous and inertial regimes of the porous material thanks to a finite element method. 20 HR has two main effects: (1) an additional internal resonance, that dominates the absorbing material response at f r ;…”

“…(2) another additional resonance, that dominates the absorbing properties at higher frequencies. 20 Both effects will be investigated in order to enhanced absorption on a wide frequency range without long-wavelength limitation. The paper is organized as follows: The configurations and the main assumptions are described and a parametric study is then presented; Finally, experimental validations are proposed.…”

Recent advances in building acoustics: An overview of prediction methods and their applications

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Design of metaporous supercells by genetic algorithm for absorption optimization on a wide frequency band

“…The effect on the absorption properties of a periodic embedment of both non-resonant and resonant inclusions in a porous layer has been studied in two (or three) dimensions, when the porous layer is either backed by a rigid backing [6][7][8][9], possibly incorporating cavities [10], or radiating in a semi-infinite half-space [11] in the case of transmission problems. Different inclusion shapes have been studied [6,7,12,13] showing similar results at low frequencies.…”