Optimised thin Metaporous materials for absorption applications in the audible frequency range
Invited paper
LAUM UMR 6613
Tuesday 2 june, 2015, 11:00 - 11:20
0.7 Lisbon (47)
Abstract:
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.