Enhancing the absorption coefficient of a backed rigid frame porous layer by embedding circular periodic inclusions.
The acoustic properties of a porous sheet of medium static air flow resistivity (around 10,000 N m s(-4)), in which a periodic set of circular inclusions is embedded and which is backed by a rigid plate, are investigated. The inclusions and porous skeleton are assumed motionless. Such a structure behaves like a multi-component diffraction grating. Numerical results show that this structure presents a quasi-total (close to unity) absorption peak below the quarter-wavelength resonance of the porous sheet in absence of inclusions. This result is explained by the excitation of a complex trapped mode. When more than one inclusion per spatial period is considered, additional quasi-total absorption peaks are observed. The numerical results, as calculated with the help of the mode-matching method described in this paper, agree with those calculated using a finite element method.
Laboratoire d'Acoustique de l'Université du Maine, UMR6613 CNRS/Université du Maine, Avenue Olivier Messiaen, F-72085 Le Mans Cedex 9, France. Jean-Philippe.Groby@univ-lemans.fr
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Duclos
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Boeckx
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