Optimised thin Metaporous materials for absorption applications in the audible frequency range

Invited paper

Clément Lagarrigue


Tuesday 2 june, 2015, 11:00 - 11:20

0.7 Lisbon (47)

With the need of better acoustic quality, several solutions have been developed to enhance the global performances of the acoustic materials, because the usual solution, i.e., multilayer package, still suffers from a lack of efficiency in the low frequency range. Metaporous materials constitutes an efficient alternative, in particular with the low frequency issue. In this paper, optimized metaporous materials with high broad band absorption in the audible frequency range are designed. They are composed of resonant inclusions (Helmholtz or split ring resonators) periodically embedded in a porous matrix glued on a rigid backing that can incorparte resonant cavities (quarter wavelength or Helmholtz resonators). The correct combination of several local resonances and of the porous material results in a large absorption over a wide frequency band. It can absorb, in particular, wavelength up to ten times larger than its thickness. Because all resonant phenomena strongly interact one with each other and are linked to the geometry and material parameters of the whole structure, the number of possible configurations is infinite. To design those which reach the best acoustic efficiency, an in-home program, combining genetic algorithm optimization and finite element method has been developped and used. To better understand how each elements influence the acoustic response we started from a simple configuration and complexify progressively the geometries. The so designed metaporous material almost totaly absorb sound over a frequency range of 1500 Hz to 7000 Hz with a very small thickness when compared to the largest absorbed wavelength.

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