Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

Porous layer impedance applied to a moving wall: Application to the radiation of a covered piston

International audienceModelling a porous layer mounted on a vibrating wall by mean of an acoustic impedance is investigated in this paper. It is shown that the use of the surface impedance usually measured with the impedance tube method can provide erroneous estimation of the acoustic pressure radiated by the coated structure. The paper focuses on the derivation of an impedance, denoted the ”transfer impedance”, which describes accurately the dynamic movement of the porous layer. Biot's theory is used in the model to account for deformations in the thickness of the layer. Experimental validation is performed using a circular piston covered by a foam or a fibrous layer and radiating in a infinite halfspace. The radiation model including the transfer impedance shows good agreement with experimental data

How reproducible are methods to measure the dynamic viscoelastic properties of poroelastic media?

There is a considerable number of research publications on the acoustical properties of porous media with an elastic frame. A simple search through the Web of Science™ (last accessed 21 March 2018) suggests that there are at least 819 publications which deal with the acoustics of poroelastic media. A majority of these researches require accurate knowledge of the elastic properties over a broad frequency range. However, the accuracy of the measurement of the dynamic elastic properties of poroelastic media has been a contentious issue. The novelty of this paper is that it studies the reproducibility of some popular experimental methods which are used routinely to measure the key elastic properties such as the dynamic Young's modulus, loss factor and Poisson ratio of poroelastic media. In this paper, fourteen independent sets of laboratory measurements were performed on specimens of the same porous materials. The results from these measurements suggest that the reproducibility of this type of experimental method is poor. This work can be helpful to suggest improvements which can be developed to harmonize the way the elastic properties of poroelastic media are measured worldwide

Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

Effect of porous material compression on the sound transmission of a covered single leaf panel

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A systematic link between microstructure and acoustic properties of foams: A detailed study on the effect of membranes

International audienceIn this study, we show how milli-fluidic tools can be used to elaborate polymer foams with tunable microstructural parameters, such as the size and the connectivity of the pores. We produce several samples having the same density and the same monodisperse pore size but different values of the closure rate of the windows separating the foam pores, which is estimated by measuring the proportion of closed cells and the size distribution of apertures for open-wall cells. This distribution is based on a distinction between the windows counting four or less edges from the windows counting more than four edges. Then a representative unit cell is reconstructed to mimic the main feature of microstructure information and serves as the basis to the computation of the sound absorbing parameter, using numerical homogenization techniques. Very good correspondences between numerical results and experimental measurements were observed. Our analysis reveals a significant dependence of membrane level on the sound absorption behavior of these foams

Estimation of the ear canal displacement field due to in-ear device insertion using a registration method on a human-like artificial ear

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