Search results for "ACOUSTIC"
showing 10 items of 1590 documents
Numerical vibroacoustic analysis of plates with constrained-layer damping patches
2011
International audience; A numerical vibroacoustic model that can manage multilayered plates locally covered with damping patches is presented. All the layers can have an on-axis orthotropic viscoelastic behavior. Continuity of displacements and transverse shear stresses at each interface is enforced, which permits to write the entire displacement field in function of the displacements of the-common-first layer, leading to a two-dimensional plate model. The problem is then discretized by Rayleigh-Ritz's method using a trigonometric basis that includes both sine and cosine functions in order to treat various boundary conditions. The excitation can be of mechanical kind (concentrated or distri…
Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy.
2015
International audience; The origin of the martensitic transition in the magnetic shape memory alloy Ni-Mn-Ga has been widely discussed. While several studies suggest it is electronically driven, the adaptive martensite model reproduced the peculiar nonharmonic lattice modulation. We used femtosecond spectroscopy to probe the temperature and doping dependence of collective modes, and scanning tunneling microscopy revealed the corresponding static modulations. We show that the martensitic phase can be described by a complex charge-density wave tuned by magnetic ordering and strong electron-lattice coupling.
Optical force rectifiers based on PT-symmetric metasurfaces
2018
We introduce here the concept of optical force rectifier based on parity-time symmetric metasurfaces. Directly linked to the properties of non-Hermitian systems engineered by balanced loss and gain constituents, we show that light can exert asymmetric pulling or pushing forces on metasurfaces depending on the direction of the impinging light. This generates a complete force rectification in the vicinity of the exceptional point. Our findings have the potential to spark the design of applications in optical manipulation where the forces, strictly speaking, act unidirectionally. R.A. and B.G. would like to acknowledge financial support from the Max Planck Society. J.C. acknowledges the suppor…
Entangled photons through thick scattering media: experiments and comparison with simulations of the biphoton wave function
2021
International audience; We report experimentally and numerically quantum correlations imaging through thick random media. We demonstrated that spatial correlations between twin photon are still detected but no in form of two-photon speckle-like patterns.
Numerical Optimization of Liner Impedance in Acoustic Duct
2020
Abstract The SALUTE project aims at evaluating performance of metacomposites for acoustic smart lining in grazing turbulent flow. Theoretical and numerical investigations are carried out for designing innovative specimen. A specific focus is placed in the realization of prototypes for evaluating the metacomposite liner performances in 2D and 3D liners, its process complexity and robustness. The insight gain in this project is new tools for obtaining innovative samples; the acoustical experimental tests demonstrate efficiency and robustness of such technology for controlling UHBR noise emission. This paper is focused on parametric study based on the maximization of the absorption coefficient…
Tungsten oxide thin films sputter deposited by the reactive gas pulsing process for the dodecane detection
2015
International audience; The DC reactive magnetron sputtering of a metallic tungsten target was performed in an argon + oxygen atmosphere for depositing tungsten oxide thin films. In order to control the oxygen concentration in the films, the reactive gas pulsing process, namely RGPP, was implemented. Rectangular pulses were used with a constant pulsing period T = 16 s whereas the duty cycle α (time of oxygen injection to pulsing period T ratio) was systematically changed from 0 to 100% of T. This pulsing injection of the reactive gas allowed a gradual evolution of the films composition from pure metallic to over-stoichiometric WO3+ɛ’ compounds. These WOx films were sputter deposited on comm…
The mKdV equation and multi-parameters rational solutions
2021
Abstract N -order solutions to the modified Korteweg–de Vries (mKdV) equation are given in terms of a quotient of two wronskians of order N depending on 2 N real parameters. When one of these parameters goes to 0, we succeed to get for each positive integer N , rational solutions as a quotient of polynomials in x and t depending on 2 N real parameters. We construct explicit expressions of these rational solutions for orders N = 1 until N = 6 .
Propriétés acoustiques de matériaux poreux saturés d'air incluant une porosité partiellement ouverte
2010
International audience; Nous étudions les propriétés d'un matériau à microgéométrie complexe incluant une porosité partiellement ouverte ou de culs-de-sacs. Ce type de matériau peut être obtenu par dissolution de grains de sel (NaCl) noyés dans une matrice de métal solidifié. Cette matrice est obtenue après invasion sous pression négative et à haute température des grains de sels par le métal sous forme liquide, puis refroidissement jusqu'à solidification du métal. La comparaison des résultats expérimentaux et théoriques sur le coefficient d'absorption acoustique d'une couche de ce métal poreux montre que le modèle de Biot-Johnson-Allard ne fournit pas des résultats aussi satisfaisants que …
Transparent boundary condition for acoustic propagation in duct with bulk-reacting liner
2012
International audience; The proposed study focuses on the modeling of acoustic wave propagation in infinite guides lined with bulk-reacting sound absorbing material which allows acoustic propagation through the lining. The finite element method is used, it is then necessary to limit the numerical domain by an artificial boundary on which a transparent boundary condition is introduced. The method described in this work consist to write the transparent condition as a Dirichlet to Neumann operator (DTN) based on a modal decomposition of the pressure in the guide. This study is a generalization of recent works with absorbent materials modeled with impedances boundary condition. The presented me…
Opérateur DtN pour les guides cylindriques à paroi traitée en présence d'un écoulement uniforme
2010
National audience; On s'intéresse au problème de rayonnement acoustique d'une source dans une conduite cylindrique axisymétrique infinie dont la paroi est recouverte d'un matériau absorbant en présence d'un écoulement uniforme. Dans le but d'utiliser la méthode des éléments finis, le domaine infini doit être tronqué par une frontière artificielle sur laquelle une condition limite transparente est introduite. La méthode exposée dans ce travail consiste à écrire la condition transparente sous la forme d'un opérateur Dirichlet to Neumann (DtN) obtenu par la généralisation de travaux réalisés dans le cas d'un guide 2D infini. Cet opérateur est basé sur une décomposition modale qu'il est facile …