111 results on '"Derode, Arnaud"'
Search Results
102. Partial coherence of transient ultrasonic fields in anisotropic random media: Application to coherent echo detection
- Author
-
Derode, Arnaud, primary and Fink, Mathias, additional
- Published
- 1997
- Full Text
- View/download PDF
103. Robust Acoustic Time Reversal with High-Order Multiple Scattering
- Author
-
Derode, Arnaud, primary, Roux, Philippe, additional, and Fink, Mathias, additional
- Published
- 1995
- Full Text
- View/download PDF
104. Telecommunication in a disordered environment with iterative time reversal
- Author
-
Montaldo, Gabriel, Lerosey, Geoffroy, Derode, Arnaud, Tourin, Arnaud, de Rosny, Julien, and Fink, Mathias
- Abstract
We present a method to transmit digital information through a highly scattering medium in a MIMO-MU (multiple input multiple output multiple users) context. It is based on iterations of a time-reversal process, and permits us to focus short pulses, both spatially and temporally, from a base antenna to different users. This iterative technique is shown to be more efficient (lower inter-symbol interference and lower error rate) than classical time-reversal communication, while being computationally light and stable. Experiments are presented: digital information is conveyed from 15 transmitters to 15 receivers by ultrasonic waves propagating through a highly scattering slab. From a theoretical point of view, the iterative technique achieves the inverse filter of propagation in the subspace of non-null singular values of the time-reversal operator. We also investigate the influence of external additive noise, and show that the number of iterations can be optimized to give the lowest error rate.(Some figures in this article are in colour only in the electronic version)
- Published
- 2004
- Full Text
- View/download PDF
105. Multiple scattering of sound
- Author
-
Tourin, Arnaud, Fink, Mathias, and Derode, Arnaud
- Abstract
We present a topical review which summarizes the main contributions to 'multiple scattering of acoustic and elastic waves' including the most recent advances. The review is divided into five main parts. In the first part, the effects of multiple scattering on ultrasonic propagation are illustrated on the basis of three experimental examples. In the second and third parts, we present the two possible descriptions for the propagation of an acoustic wave in a random medium. The first one is based on the study of the coherent wave, i.e. the wave amplitude averaged over disorder, whereas the second one deals with the propagation of the incoherent intensity, i.e. the intensity averaged over disorder. We especially insist on the microscopic basis for the phenomenological radiative transfer equation and show how it can be solved in the diffusion approximation. The theory is illustrated with experimental results obtained on a two-dimensional multiple-scattering prototype made of thousands of steel rods randomly distributed and immersed in water. In the fourth part, we present experimental evidence that the diffusion equation fails in describing all the aspects of the propagation of an acoustic wave in a random medium: e.g. the coherent backscattering effect recently observed for ultrasonic waves. We show that this effect arises as a consequence of reciprocity. Finally, in the fifth part, we discuss another property which is not taken into account in the radiative transfer theory: the reversibility of an acoustic wave propagating in a disordered medium.
- Published
- 2000
- Full Text
- View/download PDF
106. Local measurements of the diffusion constant in multiple scattering media: Application to human trabecular bone imaging.
- Author
-
Aubry, Alexandre, Derode, Arnaud, and Padilla, Frédéric
- Subjects
- *
DIFFUSION , *SCATTERING (Physics) , *MEDICAL imaging systems , *TRANSDUCERS , *BACKSCATTERING - Abstract
We present local measurements of the diffusion constant for ultrasonic waves undergoing multiple scattering. The experimental setup uses a coherent array of programmable transducers. By achieving Gaussian beamforming at emission and reception, an array of virtual sources and receivers located in the near field is constructed. A matrix treatment is proposed to separate the incoherent intensity from the coherent backscattering peak. Local measurements of the diffusion constant D are then achieved. This technique is applied to a real case: a sample of human trabecular bone for which the ultrasonic characterization of multiple scattering is an issue. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
107. NUMERICAL AND EXPERIMENTAL TIME-REVERSAL OF ACOUSTIC WAVES IN RANDOM MEDIA.
- Author
-
DERODE, ARNAUD, TANTER, MICKAËL, TOURIN, ARNAUD, SANDRIN, LAURENT, and FINK, MATHIAS
- Subjects
CLASSICAL mechanics ,SCATTERING (Physics) ,THEORY of wave motion ,DIFFUSION ,INVARIANTS (Mathematics) - Published
- 2004
108. Diffusion multiple résonante des ondes ultrasonores dans des milieux désordonnés
- Author
-
Tallon, Benoit, Institut de Mécanique et d'Ingénierie de Bordeaux (I2M), Institut National de la Recherche Agronomique (INRA)-Université de Bordeaux (UB)-École Nationale Supérieure d'Arts et Métiers (ENSAM), Arts et Métiers Sciences et Technologies, HESAM Université (HESAM)-HESAM Université (HESAM)-Arts et Métiers Sciences et Technologies, HESAM Université (HESAM)-HESAM Université (HESAM)-Institut Polytechnique de Bordeaux-Centre National de la Recherche Scientifique (CNRS), Université de Bordeaux, Christophe Aristégui, Thomas Brunet, École Nationale Supérieure d'Arts et Métiers (ENSAM), HESAM Université (HESAM)-HESAM Université (HESAM)-Institut Polytechnique de Bordeaux-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut National de la Recherche Agronomique (INRA), Arnaud Derode [Rapporteur], Vincent Tournat [Rapporteur], Aristégui, Christophe, Brunet, Thomas, Derode, Arnaud, Tournat, Vincent, and STAR, ABES
- Subjects
Ultrasonic waves ,Ondes ultrasonores ,Coherent wave ,[PHYS.COND.CM-GEN] Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other] ,Trans- port dffusif des ondes acoustiques ,[PHYS.COND.CM-GEN]Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other] ,Onde cohérente ,Resonant multiple scattering ,Diffusion multiple résonante ,Localisation des ondes acoustiques - Abstract
Complex physical phenomena study, such as resonant multiple scattering of waves, requireswell calibrated model systems. During this study, we suggest the use of resonant emulsions tostudy ultrasonic waves transport in strongly resonant disordered media. Emulsions components(uorinated oil droplets in a water-based gel) were selected for both their weak absorptionand propensity to generate strong Mie-type resonances. Fluid kind of those systems allowsfurthermore in situ acoustic _eld probing.First, we theoretically describe acoustic waves propagation in resonant emulsions. Dropletsresonance modes are calculated just as multiple scattering of an acoustic wave by a disorderedpopulation of identical objects. Then, micro-uidic technics used to make such model systemsare described as well as acoustic devices designed for both coherent and incoherent waves characterization.For diluted emulsions, our experimental observations of both the ballistic propagation ofcoherent wave and di_usive transport of averaged intensity are well described by independentscattering approximations. Energy velocity estimation of multiple scattered waves allows thenan original link between pioneering works in optics and acoustics.Finally, when scatterers concentration increases, previous approximations fail. We thus observefurther complex phenomena, which arise from scatterers interactions, such as\sub-di_usive"transport of averaged intensity suggesting attractive prospects for Anderson localization study., La compréhension de phénomènes physiques complexes tels que la diffusion multiple résonante des ondes nécessite l'étude de systèmes modèles parfaitement contrôlés. Lors de ces travaux de thèse, nous proposons l'utilisation d'émulsions résonantes pour l'étude du transport des ondes ultrasonores en milieux désordonnés fortement diffusants. Les constituants de ces émulsions (gouttetelettes d'huile fluorée dispersées dans un gel aqueux) ont été choisis pour leur caractère très faiblement absorbant et leur propension à engendrer de très forte résonances de type-Mie. De plus, la nature fluide de ces systèmes autorise l'exploration in situ du champ acoustique dans le milieu. Dans un premier temps, nous nous attachons à la description théorique de la propagation des ondes acoustiques dans des émulsions résonantes. Les modes de résonance d'une goutte isolée sont tout d'abord modélisés avant d'étudier la diffusion (simple et multiple) d'une onde acoustique par une population désordonnée d'objets identiques. Les techniques micro-fluidiques employées pour la synthèse de ces systèmes modèles sont ensuite déc rites, de même que les dispositifs acoustiques mis en place pour la caractérisation des ondes cohérentes et incohérentes. Pour des émulsions diluées, les résultats de ces caractérisations sont analysés dans le cadre d'hypothèses de diffusion indépendante, adaptées aux descriptions de la propagation balistique de l'onde cohérente et du transport diffusif de l'intensité incohérente moyenne. L'estimation expérimentale de la vitesse de l'énergie des ondes multiplement diffusées permet d'établir un lien original entre de précédents travaux menés en optique et en acoustique. Enfin, lorsque la concentration en diffuseurs augmente, les approximations évoquées précédemment sont mises en défaut. Nous observons alors des phénomènes physiques plus complexes liés à l'interaction entre diffuseurs, comme le transport "sub-diffusif" de l'intensité moyenne laissant entrevoir des perspectives séduisantes quant à l'étude du phénomène de locations d'Anderson
- Published
- 2017
109. Caractérisation ultrasonore d'échantillons hétérogènes multiplement diffuseurs
- Author
-
Mamou, Victor, Laboratoire Ondes et Acoustique (UMR 7587) (LOA), Université Paris Diderot - Paris 7 (UPD7)-Ecole Superieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Diderot - Paris VII, Derode Arnaud, and Mamou, Victor
- Subjects
milieu effectif ,ultrasons ,diffusion multiple ,milieux hétérogènes ,approximation de la diffusion ,[PHYS.MECA.ACOU] Physics [physics]/Mechanics [physics]/Acoustics [physics.class-ph] ,rétrodiffusion cohérente ,corrélations ,[PHYS.MECA.ACOU]Physics [physics]/Mechanics [physics]/Acoustics [physics.class-ph] - Abstract
In this thesis, we studied various aspects of ultrasonic multiple scattering in random media. Experimentally, we worked on prototype media made up of thousands vertical steel stems randomly distributed in the plane, as well as "real" samples like trabecular bones and metal alloys used in industry. In the first chapter, we present the effective media theory and undertake experiments of coherent transmission. The effect of absorption and correlations between scatterers is discussed by comparing several theoretical approaches. in fine, we obtain an evaluation of the elastic mean free path versus frequency. the second chapter deals with the time-resolved multiply scattered intensity. First of all, we show that the coherent backscattering effect allows to measure the diffusion coefficient D in a reliable way and independently from intrinsic absorption. Secondly, the time of flight distribution in transmission enables us to evaluate absorption losses. The third chapter is devoted to the stationary regime : we show that the transport mean free path cannot be evaluated by the coherent backscattering effect under our experimental conditions. Lastly, the limits of time reversal focusing in resonant scattering media is discussed., Dans cette thèse, nous avons étudié divers aspects de la diffusion multiple des ultrasons dans les milieux désordonnés. Expérimentalement, nous avons travaillé sur des milieux prototypes composés de milliers de tiges d'acier verticales aléatoirement réparties dans le plan, ainsi que sur des échantillons "réels" comme des os trabéculaires et des alliages métalliques utilisés dans l'industrie. Dans le premier chapitren nous exposons la théorie des milieux effectifs et meons des expériences de transmission cohérente. La prise en compte de l'absorption et des corrélations entre diffuseurs est discutée en comparant plusieurs approches théoriques. In fine, nous obtenons une évaluation fréquentielle du libre parcours moyen élastique. Le second chapitre s'intéresse à l'intensité diffusée en régime dynamique. Nous montrons tout d'abord que l'effet de rétrodiffussion cohérente permet de mesurer le coefficient de diffusion D de manière fiable et indépendante de l'absorption intrinsèque. Dans un second temps, l'étude de la courbe des temps de vol en transmission nous permet d'évaluer les pertes par absorption. Le troisième chapitre traite du régime stationnaire : nous montrons que dans ce régime, l'effet de rétrodiffusion cohérente ne permet pas d'évaluer le libre parcours moyen de transport dans nos conditions expériementales. Enfin, les limites de la focalisation par retournement temporel en milieu multiplement diffuseur sont abordées.
- Published
- 2005
110. Temperature-dependent diffusing acoustic wave spectroscopy with resonant scatterers.
- Author
-
Leroy V and Derode A
- Abstract
The influence of a slight temperature change on the correlation of multiply scattered acoustic waves is studied, and experimental results are discussed. The technique presented here, similar to diffusing-acoustic-wave spectroscopy, is based on the sensitivity of a multiply scattering medium to a slight change. Ultrasonic waves around 3 MHz are transmitted through a sample made of steel rods in water and recorded by an array of transducers at different temperatures. The cross correlations between highly scattered signals are computed. The main effect of the temperature change is a simple dilation of the times of arrival, due to a change of the sound velocity in water. But the scatterers also play a role in the progressive decorrelation of wave forms. An analysis resolved in both time and frequency shows that at some particular frequencies, the resonant behavior of the scatterers is responsible for a significantly larger decorrelation. Interestingly, the experimental results allow one to detect the presence of a small resonance that was not detected earlier on the same scatterers with classical measurement of the scattering mean free path. A simple model is proposed to interpret the experimental results.
- Published
- 2008
- Full Text
- View/download PDF
111. Relation between time reversal focusing and coherent backscattering in multiple scattering media: a diagrammatic approach.
- Author
-
de Rosny J, Tourin A, Derode A, van Tiggelen B, and Fink M
- Abstract
In this paper, we revisit one-channel time reversal (TR) experiments through multiple scattering media in the framework of the multiple scattering theory. The hyperresolution and the self-averaging property are retrieved. The developed formalism leads to a deeper understanding of the role of the ladder and most-crossed diagrams in a TR experiment and also establishes the link between TR and coherent backscattering (CBS). Especially, we show that when the initial source and the time reversal point are at the same location, the time-reversed amplitude is twice higher. Surprisingly, this enhancement is due to the ladder diagrams and not to the most-crossed ones, contrary to CBS. These theoretical predictions are confirmed by experimental results. The experiments are performed with ultrasonic waves propagating through a random collection of parallel steel rods.
- Published
- 2004
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.