The activities of the Acoustics and Mechanics of Porous Materials research group were initiated in the 80’s by the research of J. F. Allard (Professor at the University of Le Mans till he retired in 2011). Prof. J.F. Allard received the Biot medal in 2008 and the Decibel d’Or special price in 2011 for his contribution in the modeling of acoustic wave propagation in air saturated porous materials.
Nowadays, the activities of our group focus on the acoustics and dynamic behavior of sound absorbing complex materials, mostly involving porous materials saturated by air, but also some specific research is conducted on porous materials saturated by heavy fluids, like water (bone modeling, geophysics...).
The activities are organized around three topics which are highly interconnected :
The usual characterization procedures for the recovery of the acoustic and non acoustic parameters of the Johnson-Champoux-Allard model (flowmeter, standard diameter impedance tubes, ultrasounds) and of the mechanical parameters (rigidimeter) have been transfered to the acoustic group of CTTM.
The activities of the research group regarding the characterization of porous materials now focus on :
the recovery of the Pride-Lafarge model parameters by use of a specially designed impedance sensor (see Figure 1) jointly developed by LAUM and CTTM. These parameters are particularly important for the low frequency modeling of the porous materials behavior. This work is conducted in collaboration with CTTM
Besides some of the widely used models to describe the acoustic propagation in air saturated porous materials developed at the Laboratory (Johnson-Champoux-Allard model or Pride-Lafarge model), the modeling of porous metamaterials is currently of particular importance. A nonlocal model accounting for both time and spatial dispersion of the acoustic propagation in acoustic metamaterials has been recently developed in the laboratory and is currently one of the most relevant ongoing work of the group on physical models.
Regarding numerical modeling of the acoustic wave propagation in structure involving porous materials various in-house codes have been developed :
Classical sound absorbing porous materials suffer from a lack of absorption at low frequency, when compared to their efficiency at higher frequency. This is due to the intrinsic absorption mechanisms, which only rely on the viscous and thermal losses. To enhance the absorption of porous based complex structures, porous materials should be combined with volume or surface heterogeneities. The excitation of the resonances due to the presence of heterogeneities and/or to the resonant heterogeneities themselves induces a localization of the energy inside the structures and therefore an enhancement of absorption properties.
Several configurations are studied as a first step :
The second step consists of embedding inclusions, possibly resonant (spli-ring or Helmholtz resoantors), inside porous materials, and possibly coupled with surface irregularities leading to metaporous materials. These metaporous materials present quite enhanced absorption properties. Sound absorption can be higher than 0.9 for wavelength 10 times larger than the thickness of the structures, see for example Figures 3 and 7. This research is conducted in collaboration with the University of Salford and Supmeca.
Some movies showing the snapshot of the pressure field inside the unit cell as a function of frequency along the absorption curve can be found on youtube in the case of :
WO2015028760 (A1) - ACOUSTIC PANEL, published in march 2015. Inventors : C. Lagarrigue, J.-P. Groby, V. Tournat, O. Dazel, and B. Nennig