Diffusion multiple et non linéarité sont deux phénomènes antagonistes en acoustique, ilest ainsi rare d’observer un couplage de ces deux effets. En acoustique, les effets non linéaires sontimportants souvent lorsqu’ils sont cumulatifs, or la diffusion multiple modifie la relation de dispersiondu milieu et empêche ainsi ce caractère cumulatif. Les bulles sont connues pour avoir un comportementnon linéaire. Elles sont aussi de très bons diffuseurs avec une section efficace de diffusion qui est trèsgrande devant leur section efficace géométrique notamment à leur fréquence de résonance. Les milieuxbulleux semblent ainsi de bons candidats pour observer de la diffusion multiple en régime non linéaire.Trois régimes sont observables dans un milieu bulleux : un régime basse fréquence auquel les effetsnon linéaires sont importants et cumulatifs mais sans diffusion multiple, un régime à la fréquence derésonance des bulles auquel les effets non linéaires ne sont pas cumulatifs mais restent quand mêmeélevés tout comme la diffusion bien qu’atténuée par l’absorption du milieu, et enfin un régime hautefréquence pour lequel les effets de diffusion multiple sont importants mais les effets non linéaires sontabsents. Les travaux décrits dans cette thèse ont porté sur la modélisation et l’expérimentation desrégimes à la fréquence de résonance et à haute fréquence. A haute fréquence, l’observation d’une codadans les milieux bulleux est modélisée par une équation de diffusion. A la fréquence de résonance, lamodélisation, validée par les expériences, conduit ensuite à des applications qui sont : le doubleur defréquence, la diode acoustique et le miroir à conjugaison de phase. / Multiple scattering and non linear effects are antagonists so it is not commun to observea coupling of those two effects. In acoustics, non linear effects are important when they are cumulative,therefore dispersion relation is modified by multiple scattering and non linear effects cannotbe cumulative. Bubbles are known to have a non linear behavior and also to be good scatterers witha scattering cross section higher than the geometric cross section at resonance frequency. Therefore,bubbly media seem to be good to observe multiple scattering in non linear regime. A bubbly-mediumhas three different regimes. At low frequency, non linear effects are important and cumulative butthere is no multiple scattering effects. At bubbles resonance frequency, non linear behavior and alsomultiple scattering effects are important but the non linear effects cannot be cumulative. At high frequency,multiple scattering effects are important but without no non linear effects. The experimentsin this thesis show, on the one hand, a high frequency wave propagating in a bubbly-medium andon the other hand, the resonance frequency wave propagation. At high frequency, a coda is observedin experiment and modeled by a diffusion equation. At resonance frequency, the model, confirmed bythe experiments, leads us to some applications : acoustic frequency doubler, acoustic diode and phaseconjugation mirror.

Analytic methods of elastic wave scattering in fiber-reinforced composite materials are investigated in this study to calculate the effective static stiffness (axial shear modulus, m) and wave properties (axially shear wave speed, B and attenuation, Y) in composites. For simplicity only out-of-plane shear waves are modeled propagating in a plane transverse to the fiber axis. Statistical averaging of a spatially random distribution of fibers is performed and a simultaneous system of linear equations are obtained from which the effective global wave numbers are numerically calculated. The wave numbers, K=Re(K)+iIm(K), are complex numbers where the real parts are used to compute the effective axial shear static stiffness and wave speed; the imaginary parts are used to compute the effective axial shear wave attenuation in composites. Three major parts of this study are presented. The first part is the discussion of multiple scattering phenomena in a successive-events scattering approach. The successive-events scattering approach is proven to be mathematically exact by comparing the results obtained by the many-bodies-single-event approach. Scattering cross-section is computed and comparison of the first five scattering orders is made. Furthermore, the ubiquitous quasi-crystalline approximation theorem is given a justifiable foundation in the fiber-matrix composite context. The second part is to calculate m, B and Y for fiber-reinforced composites with interfacial layers between fibers and matrix. The material properties of the layers are assumed to be either linearly or exponentially distributed between the fibers and matrix. A concise formula is obtained where parameters can be computed using a computationally easy-to-program determinant of a square matrix. The numerical computations show, among other things, that the smoother (more divisional layers), or thinner, the interfacial region the less damped are the composite materials. Additionally composites with exponential order distribution of the interfacial region are more damped than the linear distribution ones. The third part is to calculate m, B and Y for fiber-reinforced composites with interfacial cracks. The procedures and computational techniques are similar to those in the second part except that the singularity near the crack tip needs the Chebychev function as a series expansion to be adopted in the computation. Both the interfacial layers and interfacial crack cases are analyzed in the low frequency range. The analytic results show that waves in both cases are attenuated and non-dispersive in the low frequency range. The composites with interfacial layers are transversely isotropic, while composites with interfacial cracks are generally transversely anisotropic. / Ph. D.

No description available.

Ce travail de thèse présente une étude numérique et théorique de l’influence des effets coopératifs sur la localisation de la lumière dans des vapeurs atomiques, suivie d’une étude expérimentale de ces effets coopératifs dans le régime de diffusion multiple dans des nuages d’atomes froids dilués. Le premier chapitre décrit le modèle que nous utilisons, basé sur l’Hamiltonien effectif d’interaction matière rayonnement, afin d’étudier numériquement la localisation de la lumière et les effets coopératifs. Nous discutons également des différences fondamentales existant entre la situation réelle où la lumière est assimilée à une onde vectorielle et l’approximation scalaire plus facile à traiter analytiquement. Le deuxième chapitre se concentre sur la présentation des résultats numériques complétée d’une comparaison systématique entre les cas scalaire et vectoriel. Nous remarquons dans cette partie que l’approximation scalaire, valable dans la limite des milieux spatialement dilués, présente des différences drastiques avec le cas vectoriel lorsque nous considérons des milieux spatialement denses. Nous n’observons pas également d’indications suffisantes nous permettant de discriminer le fait que les effets coopératifs ne soient pas à la base des mécanismes de localisation de la lumière. Dans la dernière partie nous nous intéressons expérimentalement aux signatures des effets coopératifs dans le régime de diffusion multiple en confrontant à nos résultats expérimentaux plusieurs approches théoriques tenant compte ou pas des effets d’interférences. / In this thesis we present a numerical and theoretical study of the interplay between cooperative effects and light localization in atomic vapour, completed by an experimental study of these cooperative effects for dilute cold atom clouds in the multiple scattering regime. The first chapter describes the model we use, based on the light matter effective Hamiltonian, in order to investigate numerically light localization and cooperative effects. We also discuss the fundamental differences existing between the real situation where light is considered as a vector wave and its scalar approximation easier to treat analytically. The second chapter focuses on the numerical results where we compare systematically the scalar and the vector cases. We show that the scalar approximation, valid for spatially dilute systems, leads to drastic differences compared to the vector case when we consider spatially dense clouds. We also do not observe sufficient proofs to establish that cooperative effects are not at the origin of light localization mechanisms. In the last chapter we investigate experimentally the signatures of cooperative effects in the multiple scattering regime, comparing our results to several theoretical approaches taking or not into account interference effects related to the wave nature of light.

Le but de cette thèse est d'étudier la propagation des ondes ultrasonores dans les milieux présentant des diffuseurs allongés, et plus particulièrement les alliages de titane comportant des macrozones. Cette étude est menée à l'aide d'un dispositif expérimental constitué d'un transducteur multi-éléments linéaire en rotation autour de son axe, piloté par une électronique multivoie programmable. Le champ rétrodiffusé par un milieu à diffuseurs allongés présente une cohérence spatiale anisotrope et nous montrons que l'intensité rétrodiffusée par un tel milieu dépend de l'orientation du transducteur dans le plan perpendiculaire à la direction d'insonification. Cette dépendance permet de déterminer la direction d'élongation des macrozones, leur taille caractéristique, et de réduire le bruit de structure lors d'un contrôle ultrasonore. Une cartographie en trois dimensions de la direction locale des macrozones est ainsi réalisable en employant deux faisceaux ultrasonores focalisés en un même point selon deux directions différentes. Afin de déterminer le régime de diffusion aux fréquences usuelles de contrôle, nous avons développé, à partir des travaux de thèse d'Alexandre Aubry (UPMC 2008), un indicateur du niveau de diffusion multiple : l'estimateur de la proportion de diffusion simple. Il permet de démontrer que la diffusion multiple est importante dans les alliages de TA6V et Ti17. Nous avons de plus étendu cette méthode au cas d'interfaces eau/solide complexes suffisamment régulières. Enfin, nous proposons une nouvelle visualisation des résultats de simulations de forge permettant d'observer la direction réelle des macrozones et de mieux concevoir les plans de contrôle. / This manuscript is devoted to the study of ultrasonic wave propagation in complex media composed of elongated scatterers, and specifically titanium alloys comprising macrozones. This study is carried out using a linear phased array probe rotating around its axis and driven by a multi-channel programmable amplifier. The ultrasonic field backscattered by elongated scatterers presents an anisotropic spatial coherence and we show that the intensity backscattered by such a medium depends on the angle between scatterers elongation direction and the orientation of the probe in the plane perpendicular to the insonified direction. This dependence allows to determine the macrozones elongation direction and size, and to reduce the structural noise during a non-destructive evaluation. A three dimensional cartography of local elongation direction of macrozones is achievable by using two beams focused at the same point but with different directions of incidence. In order to assess the scattering regime at conventional testing frequencies, we developed a multiple scattering measure: the single scattering proportion estimator, based on Alexandre Aubry’s PhD thesis (UPMC 2008). Applied on TA6V and Ti17 alloys, it showed strong multiple scattering. We further extended this estimator to the case of water/solid complex interfaces. Lastly, we proposed a new visualization of forging simulation results, allowing to directly observe the real macrozones elongation direction and to better design inspection procedures.

La propagation d’une onde ultrasonore de compression au travers d’une distribution de particules solides identiques localisées aléatoirement dans un liquide visqueux est étudiée. La longueur d’onde de l’onde de compression est supposée grande devant le rayon des particules, et les propriétés effectives dynamiques du milieu sont recherchées.Les coefficients de diffusion d’une sphère solide isolée sont étudiés pour différentes polarisations des ondes partielles de mode n incidentes et diffusées. Des expressions approchées en sont données pour tout n dans le régime de diffusion de Rayleigh.Dans le cas de particules sphériques, le milieu est modélisé par un noyau élastique, de même matériau et rayon que les particules, et entouré d’une coque emplie du fluide hôte. L’ensemble est insoné, dans le milieu effectif, par une onde de compression partielle de mode n. Les propriétés effectives sont recherchées par minimisation de la diffusion pour différentes valeurs de n. Le module d’élasticité volumique effectif et la masse volumique effective sont obtenus respectivement à partir des modes n=0 et n=1. Comparée à la formule d’Ament, fondée sur l’équilibre des forces hydrodynamiques et inertielle au niveau de chaque particule supposée rigide, celle obtenue ici fait apparaître un effet de la concentration sur la dépendance fréquentielle de la masse volumique similaire à celui observé, expérimentalement et dans des modèles de diffusion multiple, sur les propriétés effectives des ondes de compression. La méthode d’Ament est ensuite appliquée pour obtenir la masse volumique effective dans le cas de sphéroïdes rigides alignés. / A random dispersion of identical elastic solid particles in a viscous fluid is considered and effective properties, appropriate to the propagation through the medium of an ultrasonic compressional wave of large wavelength compared to the radius of the particles, is investigated.The scattering coefficients of a single spherical particle in a viscous medium are investigated for all combinations of incident and scattered wave types for use in multiple scattering models. Approximate formulae are obtained for the coefficients at n’th partial wave order in the Rayleigh limit. For spherical particles, a core-shell self-consistent model is used, in which the medium is modelled by an elastic core of the same material and radius as the particles, surrounded by a shell of the host fluid, and placed in the effective medium. The radius of the shell is such that the ratio of the core/shell volume is equal to the particle concentration. The dynamic properties of the effective medium are sought by minimising the scattering of the shell for different incident compressional partial wave orders (n).The effective bulk modulus is found from the monopole mode n=0 and the effective mass density from the dipole mode n=1. When compared to Ament’s formula based on local force balance at the particles (assumed rigid), the effective mass density obtained from the core-shell model shows a frequency-dependent effect of concentration similar to that observed in multiple scattering models and experimentally. Ament’s method is then applied to obtain the effective mass density in case of aligned rigid spheroids.

Efeitos causados pela interação da radiação ionizante em dispositivos eletrônicos consis- tem numa preocupação crescente em diversos segmentos, como as aplicações aeroespaci- ais e em física de altas energias. Entre os efeitos de radiação induzidos por íons pesados estão os chamados de Efeitos de Eventos Isolados (Single Event Effects - SEE), em que o impacto de um único íon pode ser capaz de gerar um efeito observável, através da elevada deposição de energia e consequente geração de pares elétron-lacuna. O estudo destes efeitos requer um acelerador de partículas capaz de prover feixes uniformes de íons pesados com baixo fluxo. Neste trabalho, desenvolvemos um sistema para produ- ção de feixes de íons pesados para estudar SEE no Acelerador Pelletron 8UD, utilizando as técnicas de desfocalização e espalhamento múltiplo em folhas de ouro. O sistema foi projetado para prover feixes com intensidades entre 10 2 e 10 5 partículas/s/cm 2 com uniformidade maior que 90% numa área circular de diâmetro de 1,5 cm, operando em regime de alto-vácuo. Um manipulador de amostras permite a movimentação do dispo- sitivo sob teste com precisão de 2,5 m e um sistema de aquisição de dados dedicado foi desenvolvido, permitindo a automação de medidas. O sistema foi caracterizado com feixes de 1 H, 12 C, 16 O, 19 F, 28 Si, 35 Cl e 63 Cu a várias energias, apresentando fluxo e uni- formidade adequados aos experimentos em diversas configurações de focalização e folhas espalhadoras, e tem sido utilizado por diversos grupos de pesquisa. O novo sistema foi utilizado para estudar o efeito das camadas de isolamento e metalização na coleta de carga e geração de eventos observáveis em um dispositivo analógico e em um disposi- tivo digital, de modo a estabelecer metodologias de trabalho adequadas para estudos precisos de mecanismos de ocorrência de efeitos de radiação. O dispositivo analógico estudado foi um transistor p-MOS, onde o sinal de corrente induzido pelo impacto de íons diversos foi analisado de modo a obter a seção de choque de eventos e a cargaix gerada, permitindo determinar a espessura da camada de metalização em 1,28(2) m, e a camada de coleta de carga dependente do LET e alcance da partícula incidente, variando entre 6,0 e 11,0 m. O dispositivo digital estudado foi uma memória SRAM 28nm, onde foi observada uma forte dependência da seção de choque de eventos com a penetração do feixe no dispositivo. Associando as camadas de metalização e isolamento a um meio efetivo de interação, obteve-se que toda a área sensível do dispositivo só pode ser excitada, isto é, nela ocorrerem eventos observáveis, para partículas com alcance, no meio efetivo, entre 14 e 20 m, embora partículas com alcance de até 10 m sejam capazes de sensibilizar até 50% da área ativa do dispositivo. / Effects on electronic devices caused by interactions of ionizing radiation are a main concern in several fields, such as aerospace applications and high-energy physics. Among the heavy-ion induced radiation effects are the Single Event Effects, in which a strike of a single ion can be enough to generate an observable effect, as a result of the high energy deposition and thus electron-hole pairs generation. The study of these effects requires the use of uniform, low-flux particle beams. In this work, we developed a system for production of heavy ion beams for SEE studies at Pelletron 8UD accelerator, through the defocusing and multiple scattering in gold foil techniques. The setup can provide ion beams with intensities ranging from 10 2 e 10 5 particles/s/cm 2 with uniformity better than 90% in an circular area of 1.5 cm diameter, operating under high-vacuum. A sample manipulador allows device under test positioning with a precision of 2.5 m, and a dedicated data acquisition system was developed, allowing measurement automation. The system was characterized with 1 H, 12 C, 16 O, 19 F, 28 Si, 35 Cl and 63 Cu ion beams at several energies, presenting flux and uniformity adequate for SEE studies in many different configurations, and it is being used by several research groups. The new facility was used to study the effect of isolation and metalization layers in charge collection and observable events generation in an analog and in a digital device, in order to establish proper metodologies for precise studies of radiation effects mecanisms. The analog device studied was a p-MOS transitor, from which the heavy-ion impact induced current signal was analised to obtain cross-section and colected charge, allowing to determine metalization layer thickness to be 1.28(2) m, and charge collection dependency on particle LET and range, varying from 6.0 to 11.0 m. The digital device studied was a 28nm SRAM memory, where a strong dependency of cross-section with particle range in the device was observed. Associating to the metal and insulating layers an effectivexi medium, it was observed that the complete sensitive area can be excited only by particle with ranges in effective medium between 14 and 20 m, although particles with ranges up to 10 m are capable of sensibilizing up to 50% of devices active area.

This thesis investigates analysis and simulation of the backscattering enhancement phenomenon from randomly distributed point scatterers. These point scatterers are randomly distributed within a cube or a sphere and then the backscattering enhancement phenomenon from both cubical and spherical distributions are examined throughout the thesis. The general characteristic differences between cubical and spherical distribution about the scattering phenomenon are observed. T-matrix method is used for analytic investigations of the backscattering enhancement and also a certain number of approximate formulas are obtained. As for Monte Carlo simulation method, it is used for simulated investigations of the backscattering enhancement. Some Monte Carlo simulations are prepared by using MATLAB programming language and verified by showing their confidence intervals. Both analytic and simulated investigations of the backscattering enhancement due to single and double scattering are analyzed / however, only simulated investigation of the backscattering enhancement due to multiple scattering are analyzed because of its computational complexity. The thesis traces differences between single scattering and multiple scattering from randomly distributed point scatterers. Effects of both incident field frequency and point scatterer density on the backscattering enhancement are indicated. The thesis seeks answers to questions such as which conditions cause the backscattering enhancement phenomenon from randomly distributed point scatterers, why we need to consider multiple scattering to examine the backscattering phenomenon and how we can discriminate the backscattering enhancement from the specular enhancement.

Ultrasonic wave transport in strongly scattering, disordered media is investigated via analysis of the multiply-scattered transmitted field. Measurements of transverse confinement, statistics, and correlations of the intensity were performed on an aluminum mesoglass, where aluminum beads were brazed together to form a porous slab sample. Comparison of the transverse confinement measurements with the self-consistent theory of localization was used to identify and locate a mobility edge in the sample at f = 1.1011 MHz, enabling a measurement of the critical exponent nu characterizing the Anderson transition, nu ~ 1.6–2. Infinite-range C0 correlations were observed, and observed to grow dramatically near the mobility edge, along with the C2 and C3 correlations. Measurements of the multifractal exponent Delta_2 were able to confirm the link between C0 correlations and Anderson localization. Experiments using the aluminum mesoglass with ethanol-filled pores showed evidence of two nearly-independent propagating modes, one of which appears to be characterized by a strongly renormalized diffusion coefficient. The density of states and level spacing statistics were investigated using a different mesoglass, constructed by sintering glass beads percolated on a random lattice. Direct measurements of these quantities were obtained by cutting small samples of this mesoglass, allowing individual vibrational modes to be resolved. The density of states showed a plateau extending well into the expected Debye regime, and evidence of a Boson peak was observed at low frequencies. The level spacing statistics indicated that transport in the frequency ranges measured was on the diffusive side of the mobility edge, showing agreement with the predictions of the GOE from random matrix theory. The dynamics of a suspension of bubbles were investigated using phase-based Diffusing Acoustic Wave Spectroscopy, where phase correlations were found to give additional information beyond traditional field- and intensity-based correlation measurements. / October 2015

Computer simulation of wave propagation is an active research area as wave phenomena are prevalent in many applications. Examples include wireless communication, radar cross section, underwater acoustics, and seismology. For high frequency waves, this is a challenging multiscale problem, where the small scale is given by the wavelength while the large scale corresponds to the overall size of the computational domain. Research into wave equation modeling can be divided into two regimes: time domain and frequency domain. In each regime, there are two further popular research directions for the numerical simulation of the scattered wave. One relies on direct discretization of the wave equation as a hyperbolic partial differential equation in the full physical domain. The other direction aims at solving an equivalent integral equation on the surface of the scatterer. In this dissertation, we present three new techniques for the frequency domain, boundary integral equations. / text