Measuring static viscous permeability of porous absorbing materials

International audienceConventional acoustical methods for measuring the permeability or flow resistivity of a porous material require a priori estimation of the porosity. In this work, an acoustical method is presented in which a simplified expression (independent of both the frequency and porosity) for the transmitted waves at the Darcy’s regime (low frequency range) is derived, and used for the inverse determination of both the viscous static permeability (or flow resistivity) and the thickness of air-saturated porous materials. The inverse problem is solved based on the least-square numerical method using transmitted waves in time domain. Tests are performed using industrial plastic foams. Experimental and numerical validation results of this method are presented, which show theadvantage of measuring the viscous permeability and thickness of a porous slab, without the required prior knowledge of the porosity, but by simply using the transmitted waves

Determination of the instant of glottal closure with the smoothed pseudo Wigner-Ville distribution

For several voiced speech signais, the measurement of the instant of glottal closure was get by using the smoothed pseudo Wigner-Ville distribution and the Wong method . Both methods give similar results when measurements are easy. For some difficult cases, for which the Wong method becomes unaccurate, the smoothed pseudo Wigner-Ville distribution can still be used .Pour différents signaux de parole voisée, l'instant de la fermeture de la glotte a été déterminé en utilisant la pseudo-distribution de Wigner-Ville lissée et la méthode de Wong. Les deux méthodes donnent des résultats équivalents quand cette détermination est facile . Quand la détermination devient difficile, la pseudo-distribution de Wigner-Ville lissée peut être encore employée dans certains cas où la méthode de Wong cesse d'être utilisable

Numerical results and Biot theory in anisotropic porous/fibrous media

Biot theory [l] is a basic tool when studying the propagation of elastic waves in porous/fibrous solids. Due to the simplicity of the assumptions, isotropic materials are most often utilized [2,3]. However, in some cases, anisotropy has to be included in the modelization, e.g. with some fibrous materials. In this work, we have developped routines, based on the standard Biot model, which compute the various characteristic surfaces (slowness, phase and group velocities) [4] in a given plane for anisotropic porous media. By increasing the weight of the coupling constants, one can continuously vary from the limit case of anisotropic solids with no porosity to a number of different porous media. When the coupling terms are not equal to zero, one finds four instead of three propagating modes, the two other eigenvalues being complex, meaning in turns that the two remaining solutions do correspond to some evanescent modes. The slow transverse mode is unchanged. The fourth mode often called the Biot mode [5], which is very similar to the pseudo-thermal wave [6,7] observed in dynamic thermoelasticity, has always a very small wavespeed and is very highly damped

Analyse par transformee de wigner-ville d'un signal non-uniformement echantillonne : Etude du mouvement gyroscopique d'un mobile en rotation

Nous proposons une méthode basée sur la transformation de Wigner-Ville pour déterminer les composantes instantanées du mouvement d'un mobile lancé à grande vitesse et en rotation rapide autour de son axe de symétrie ( nutation, précession, rotation propre ), soumis à des forces de frottement. Les échantillons, collectés par une sonde asservie au mouvement, sont généralement répartis non-uniformément sur l'axe des temps. L'analyse spectrale par transformation de Wigner-Ville permet le traitement direct de ces échantillons. Des exemples simulés et réels ont été réalisés

Mesure de l'instant de fermeture glottale avec la transformation de wigner-ville

Pour montrer l'intérêt de la pseudo distribution de Wigner-ville lissée dans le cas des signaux non stationnaires à structure complexe, un signal de parole voisée a été étudié simultanément avec cette transformation et la transformation de Fourier à court terme (TFCT). L'intérêt de la première transformation apparaît clairement, celle-ci permettant, contrairement à la TFCT, de mettre nettement en évidence et d'obtenir l'instant de fermeture glottale avec une bonne précision

MODÉLISATION PAR DES MATRICES DE TRANSFERT DE LA PROPAGATION DU SON DANS LES MILIEUX POREUX STRATIFIÉS

On modélise la propagation des trois ondes de Biot dans des matériaux poreux stratifiés sous incidence oblique à l'aide de matrices de transfert. On peut alors calculer l'impédance de surface de ces matériaux. Une comparaison entre mesure et calcul est donnée.The propagation of the three Biot waves in porous layered materials at oblique incidence is modelized with transfer matrices. Measurement of the surface impedance of a layered porous material at oblique incidence is compared with prediction achieved with the transfer matrix of the material

ANALYSE DES SIGNAUX DE RONFLEMENT

Le ronflement est un phénomène dont les conséquences portent à la fois sur le confort de l'entourage et sur la santé du patient. L'analyse du signal acoustique du ronflement peut révéler certains troubles cliniques. Une étude de ce signal et quelques résultats préliminaires sont présentés.Snoring is a phenomenon which may disturb both the social life and health of a patient. Acoustical analysis of snoring can be use to identify some clinical problems and we present a study of this and some preliminary results

AN APPROACH TO DIRECT AND INVERSE TIME-DOMAIN SCATTERING OF ACOUSTIC WAVES FROM RIGID POROUS MATERIALS BY A FRACTIONAL CALCULUS BASED METHOD

In this paper direct and inverse time-domain scattering of ultrasonic pulses from a rigid, homogeneous and isotropic porous medium are investigated. The Green's function of the wave propagation of a transient field in one dimensional porous media is established. The solution of direct and inverse problems are given in the time domain by using the concept of fractional derivatives. The viscous and thermal losses of the medium are described by the Johnson and Allard models [1] [2] modified to be usable in the time domain. Experimental and numerical results are given as a validation of our model

Generalized hyperbolic fractional equation for transient-wave propagation in layered rigid-frame porous materials.

5 pagesInternational audienceThis paper provides a temporal model for the propagation of transient ultrasonic waves in a layered isotropic porous material having a rigid frame. A temporal equivalent fluid model is considered, in which the acoustic wave propagates only in the fluid saturating the material. In this model, the inertial effects are described by the layered tortuosity and the viscous and thermal losses of the medium are described by two layered susceptibility kernels which depend on the viscous and thermal characteristic lengths.The medium is one dimensional ans its physical parameters (porosity, tortuosity, and characteristics lengths) are depth dependent. A generalized hyperbolic fractional equation for transient sound wave propagation in layered material is established