Ce travail de thèse a pour objectif de développer et de valider expérimentalement un modèle de diffusion adapté au sang agrégeant, prenant en compte une forte fraction volumique de globules rouges (hématocrite de 40%) et des structures d’agrégats polydisperses. Un modèle développé récemment pour l’estimation de la microstructure du sang est la théorie de milieu effectif combinée à un modèle de facteur de structure monodisperse. Pour augmenter le domaine de validité de ce modèle en hautes fréquences, nous proposons une théorie de milieu effectif prenant en compte la composante incohérente de la diffusion par des agrégats de globules rouges. A l’aide de simulation numériques tridimensionnelles, nous montrons que la nouvelle modélisation permet de prédire les coefficients de rétrodiffusion de façon satisfaisante pour un produit $kR<2$ ($k$ étant le nombre d’ondes et $R$ le rayon d’un agrégat). Par ailleurs, nous proposons une théorie de milieu effectif combinée à un facteur de structure polydisperse afin d’estimer, à partir de la mesure expérimentale du coefficient de rétrodiffusion, des paramètres de structure des agrégats : le rayon moyen de la distribution de tailles, son étalement, et la compacité des agrégats. Des expériences réalisées sur du sang de porc cisaillé dans un dispositif de Couette couplé à une sonde ultrasonore montrent que le modèle polydisperse permet d’obtenir de meilleures courbes d’ajustement des coefficients de rétrodiffusion en comparaison des modèles monodisperses classiques. Les tailles d’agrégats estimées par ultrasons sont corrélées de façon satisfaisante (r$^2$ $\approx$ 0.92) avec les tailles estimées par ailleurs dans un dispositif optique. / This thesis aims to develop and evaluate a scattering model for aggregating blood, taking into account the high volume fraction of red blood cells in blood (40%) and the polydispersity in terms of aggregate size. The effective medium theory combined with the monodisperse structure factor model was recently developed to estimate blood microstructure. In order to improve the modeling at high frequency range, we proposed an effective medium theory that takes into account the incoherent component of the scattering by aggregates of RBCs. Three dimensional simulations were performed and showed that the consideration of the incoherent component allows to approximate the simulation satisfactorily for a product of the wavenumber times the aggregates radius $kR$ up to 2. Besides, we proposed an effective medium theory combined with a polydisperse structure factor. From the measured BSC, this model allows to estimate three structural parameters: the mean radius of the aggregate size distribution, the width of the distribution, and the compactness of the aggregates. Experiments were performed on pig blood shared in a Couette device coupled with an ultrasonic probe, and showed that the polydisperse modeling provides better fitting to the experimental BSC data, when compared to the classical monodisperse models. Satisfactory correlation is obtained (r$^2$ $\approx$ 0.92) between the aggregate sizes estimated with ultrasound and the aggregate sizes estimated on the same sample in an optical device.

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<p>Nonlinear transmission lines (NLTLs) are of great interest for high power microwave (HPM) generation because they can sharpen pulses to create an electromagnetic shockwave to produce oscillations from 100 MHz to low GHz. NLTLs provide frequency agility, compactness, durability and reliability, providing a solid-state radiofrequency (RF) source for producing HPM. The essential component of NLTLs is the nonlinear material, typically a dielectric that varies with voltage or a magnetic material whose permeability varies with current, incorporated in the transmission line in various topologies. This thesis presents an alternative approach involving designing composites comprised of nonlinear dielectric inclusions (barium strontium titanate (BST)) and/or nonlinear inductive inclusions (nickel zinc ferrites (NZF)) in a polymer base host material, analogous to electromagnetic interference designs that incorporate stainless steel inclusions of various shapes in a plastic to tune the composite’s electromagnetic properties at GHz. Appropriately designing NLTL composites requires predicting these effective properties both in linear (for a fixed and low voltage and current) and nonlinear regions (permittivity and permeability become voltage dependent and current dependent, respectively) prior to designing HPM systems comprised of them. As a first step, this thesis evaluates and benchmarks composites models in the commercial software CST Microwave Studios (CST MWS) to various effective medium theories (EMTs) to predict the permittivity and permeability of composites of BST and/or NZF inclusions in the linear regime, compared with experimental measurements. The manufacturing and measurement of the nonlinear composites will be briefly discussed with an analysis of the homogeneity of a composite sample using 3D X-ray scan. Long-term application of these approaches to predicting the effective nonlinear composite permittivity and permeability and future work will be discussed.</p>

The effectiveness of the heat transfer in a geothermal reservoir strongly depends on its temperature, pressure and rock type. A porous and fractured rock is essential to provide a hot fluid circulation to a geothermal power plant. Velocity anomalies in seismic tomography may relate to the location of a fluid reservoir, hydrothermal systems, and possible heat sources. However, the subsurface properties like porosity, fracture density, and fluid state (e.g liquid, gas or supercritical fluid) cannot be inferred directly using seismic tomography. The inversion of seismic data can be combined with an effective medium model (EMM) to investigate such rock and subsurface properties. In the present study, we implement an EMM involving elastic rock properties and the following descriptions of inclusions: pore porosity, fracture density, fracture aspect ratio, fracture porosity, and liquid ratio. The chosen EMM was reproduced from the work of Adelinet et al. (2011a) and Adelinet (2010). Tomographic results were inverted for the same geographic area (Krysuvik in Iceland) in order to validate our method and to confirm the presence of the supercritical fluid reservoir. We re-evaluate the assumptions and constraining parameters choice of the inverse model used in Adelinet et al. (2011a) and Adelinet (2010), in order to 1) get a better understanding of the underlying problems, 2) investigate the sensitivity of the results based on the constraining parameters, 3) produce suitable workflows, and 4) build an adaptive method for geothermal exploration in different areas. The newly implemented method found the same qualitative results in Krysuvik as Adelinet et al. (2011a). Namely, at ≈ 6.5 km depth both values of fracture density and of liquid ratio are consistent with hydraulic fracturing and a probable super-critical fluid reservoir. Afterwards, the method was applied to the Hengill volcanic complex. Fracture density and liquid ratio values similar to those observed at Krysuvik and associated to a geothermal reservoir were obtained at Hengill at the exact location of existing production sites. Our results also showed limitations of initial assumptions and could contribute to improve the method. This study could be a starting point to build a more sophisticated tool for geothermal exploration. / Idag består majoriteten av världens energiproduktion av fossilt bränsle. Naturgas, kol och olja stod tillsammans för 70% av världens energiproduktion 2010 och det ökar konstant trots nödvändigheten att minska koldioxidutsläppen. Geotermisk energi är en hållbar resurs men bidrar endast med mindre än 2% av världens energi. Det finns dock undantag, exempelvis på Island där 70% av all energi som förbrukas kommer från geotermiska resurser. Island är en seismiskt aktiv region som inkluderar diverse olika geotermiska områden med hög temperatur. På grund av detta, har det där skett mycket forskning om geotermiska resurser. Vidare information är nödvändig för att utforska potentialen av att nyttja geotermisk energi. I denna studie impementerades en metod som kombinerar seismiska hastigheter och teoretiska mekaniska egenskaper av stenar, exempelvis stenbrottsgeometri. Metoden tillåter att uttyda egenskaper under ytan, framförallt tätheten av sprickor och det fysiska tillståndet av vätskan. Dessa egenskaper kan bidra med relevant information för beslutstagande och är nödvändiga för att lyckas med borrning. En optimering av mätna och teoeriska värden var beräknad för att hitta de optimala värdena av spricktäthet och det fysiska tillståndet av vätskan. Studien fokuserar huvudsakligen på två geotermiska områden på Island, Krysuvik- och Hengill-vulkanernas områden. Resultat erhållna från Krysuvik konfimerade en möjlig superkritisk vätskereservoar på ettdjup av 5.5-6.5 kilometer. Efter att ha studerat Hengill-området, uppkom resultat på den geotermiska utvinningsplatsen men det visade även begränsningar kring metoden. Metoden behöver förbättras och anpassa sig till funktionen av området. Heterogeniteten och de komplexa egenskaperna (till exempel bergskomposition eller vätskealternering) under ytan ledde till omvärdering av antaganden gjorda i den initiala mediummodellen.

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Gold black porous coatings were thermally evaporated in the chamber backfilled with inert gas pressure and their optical properties were studied in near-far-IR wavelengths. The porosities of coatings were found to be extremely high around ~ 99%. Different approaches of effective medium theories such as Maxwell-Garnett, Bruggeman, Landau-Lifshitz-Looyenga and Bergman Formalism were utilized to calculate refractive index (n) and extinction coefficient (k). The aging induced changes on electrical and optical properties were studied in regular laboratory conditions using transmission electron microscopy, Fourier transform infrared spectroscopy, and fore-probe electrical measurements. A significant decrease in electrical resistance in as deposited coating was found to be consistent with changes in the granular structure with aging at room temperature. Electrical relaxation model was applied to calculate structural relaxation time in the coatings prepared with different porosities. Interestingly, with aging, absorptance of the coatings improved, which is explained using conductivity form of Bergman Formulism. Underlying aim of this work was to utilize gold blacks to improve sensitivity in un-cooled IR sensors consist of pixel arrays. To achieve this, fragile gold blacks were patterned on sub-mm length scale areas using both stenciling and conventional photolithography. Infrared spectral imaging with sub-micron spatial resolution revealed the spatial distribution of absorption across the gold black patterns produced with both the methods. Initial experiments on VOx-Au bolometers showed that, gold black improved the responsivity by 42%. This work successfully establishes promising role of gold black coatings in commercial un-cooled infrared detectors.

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A near-field technique known as evanescent interferometric lithography allows for high resolution imaging. However its primary limitation is that the image exponentially decays within the photoresist due to physical limits. This thesis aims to overcome this limitation and presents a method to considerably enhance the depth of focus of images created using evanescent interferometric lithography by using a material underlay beneath the photoresist. A key enabler of this is the understanding that evanescent fields couple to surface states and operating within proximity of a resonance, the strength of the coupling allows for considerable energy extraction from the incident beam and redistribution of this energy in a photoresist cavity. This led to the analysis of the Fresnel equations, which suggested that such coupling was in fact the result of an enhanced reflectance that takes place at boundaries of carefully chosen materials. While it is known that metals and lossy dielectrics result in surface plasmon polaritons (SPP) and surface exciton polaritons (SEP) as conventional solutions to the Fresnel reflection equations for the TM polarization of light, there is no such naturally occurring surface state that allows evanescent wave enhancement with the TE polarization of light. Further investigation of the Fresnel reflection equations revealed both for TM and TE that in fact another solution exists that is but unconventional to enhance the reflectivity. This solution requires that one of the media have a negative loss. This is a new type of surface resonance that requires that one of the media be a gain medium; not one in the optical pumped sense but one that would naturally supply energy to a wave to make it grow. This new surface resonance is also a key result of this thesis. Clearly, however this is only a hypothetical solution as a real gain medium would violate the conservation of energy. However, as it is only the reflectance of this gain medium that is useful for evanescent wave enhancement, in fact a multilayered stack consisting of naturally occurring materials is one way to achieve the desired reflectivity. This would of course be only an emulation of the reflectivity aspect of the gain medium. This multilayered stack is then an effective gain medium for the reflectivity purposes when imaging is carried out at a particular NA at a particular wavelength. This proposal is also a key idea of this thesis. At λ = 193 nm, this method was used to propose a feasible design to image high resolution structures, NA = 1.85 at an aspect ratio of ~3.2. To experimentally demonstrate the enhancements, a new type of solid immersion test bed, the solid immersion Lloyd's mirror interference lithography test-bed was constructed. High quality line and space patterns with a half-pitch of 55.5 nm were created using λ = 405 nm, corresponding to a NA of 1.824, that is well in the evanescent regime of light. Image depths of 33-40 nm were seen. Next, the evanescent image was coupled to an effective gain medium made up of a thin layer of hafnium oxide (HfO) upon silicon dioxide (SiO2). This resulted in a considerable depth enhancement, and 105 nm tall structures were imaged. The work in this thesis details the construction of the solid immersion lithography test-bed, describes the implementation of the modeling tools, details the theory and analysis required to achieve the relevant solutions and understanding of the physical mechanism and finally experimentally demonstrates an enhancement that allows evanescent interferometric lithography beyond conventional limits.

Le nombre d’appareils électroniques et de systèmes de communication sans fil a considérablement augmenté au cours des 20 dernières années. Les boîtiers de blindage utilisés pour protéger les appareils électroniques contre les radiations externes, mais aussi pour limiter leurs émissions sont généralement conçus en alliages d’aluminium. Mais la nécessité de réduire le poids des aéronefs incite l’industrie aéronautique à l’utilisation de matériaux composites.La modélisation de boîtiers de blindage composés de matériaux homogènes est possible par l’utilisation d’outils numériques tels que la méthode des éléments finis. Mais la discrétisation de boîtiers constitués de matériaux composites impliquerait un nombre d’éléments trop important rendant impossible toute modélisation numérique. Le recours à l’homogénéisation semi-analytique est une possibilité pour s’affranchir de cette restriction. Les milieux homogènes équivalents obtenus avec ces méthodes peuvent être insérés dans des outils numériques pour simuler le comportement électromagnétique de boîtiers de blindage complexes. Les modèles d’homogénéisation existants, tel que le modèle de Maxwell-Garnett, sont toutefois limités a des applications quasi-statiques.La définition des propriétés effectives de matériaux composites illuminés par des ondes électromagnétiques est l’objectif principal de ce travail. Il en résulte deux méthodes d’homogénéisation dynamiques. La première introduit un effet de taille entre les fibres et la longueur d'onde. Elle permet ainsi d’étendre une méthode basée sur des problèmes d'inclusion aux micro-ondes. Mais elle reste limitée par l’apparition de l’effet de peau dans les renforts conducteurs. La seconde est basée sur la définition des pertes par effet Joule dans les fibres, permettant ainsi d’étendre la première méthode après l’apparition de l’effet de peau. Cette dernière est enfin utilisée pour modéliser le comportement électromagnétique d’un boîtier de blindage réaliste. / The number of electronic devices and wireless communication systems has significantly increased over the past 20 years. Shielding enclosures used to protect electronic devices against radiated waves and to limit their emissions are usually designed in aluminum alloys. But the need to reduce the weight of aircraft incites the aerospace industry to the use of composite materials.Modeling shielding enclosures composed of homogeneous materials is possible by the use of numerical tools such as the finite element method. But considering every details of the microstructure would involve a excessive number of unknowns preventing numerical modelings. The use of semi-analytical homogenization methods is a possibility to overcome this restriction. The equivalent homogeneous mediums obtained with these methods can be inserted into numerical tools to simulate the electromagnetic behavior of complex shielding enclosures. But classical homogenization models such as Maxwell-Garnett model, are limited to quasi-static applications.Calculating the effective properties of composite materials illuminated by electromagnetic waves is the main objective of this work. This leads to two dynamic homogenization methods. The first one introduces a size effect between the fibers and the wavelength. It allows to extend a method based on inclusion problems to microwave frequencies. However it is limited by the occurrence of the skin effect in conductive inclusions. The second consider Joule losses and extends the first method after the occurrence of the skin effect. This second homogenization method is finally used to model the behavior of a realistic shielding enclosure.