Afin de répondre aux besoins croissants d’équipements de communication pour les applications spatiales, il est important de réduire, le plus possible, la taille et la masse de l’équipement des satellites. Cela conduit à une réduction des coûts de lancement des satellites sur leur orbite ou laisse la possibilité d’ajouter des équipements dans la fusée. Ceci compte aussi pour les composants radioélectriques. L’objectif étant de réduire les dimensions sans pour autant détériorer les performances en rayonnement (directivité, polarisation croisée, bande monomode, etc.). Il est possible de contrôler la propagation des ondes électromagnétiques dans les antennes cornets et les guides d’onde à l’aide de surfaces anisotropes (corrugations, métamatériaux). Ainsi, contrairement à ce que prédisent les lois physiques sur la propagation et le rayonnement d’ondes électromagnétiques dans des structures classiques, les performances des structures à parois anisotropes peuvent être radicalement améliorées : pour le guide d’onde, réduction de la fréquence de coupure ; pour l’antenne cornet, amélioration de la directivité ou réduction du niveau des lobes secondaires. D’après l’état de l’art, même si les résultats de simulations et de mesures obtenus sont très prometteurs, le dimensionnement de la structure des métamatériaux est sujet à optimisation, donc gourmand en ressources informatiques. L’apport principal de cette thèse a été de développer une nouvelle méthodologie de conception s’appuyant sur une Théorie Modale Elargie (TME) analytique pour des guides d’onde à parois anisotropes. Elle permet de dimensionner très rapidement des surfaces à métamatériaux les plus adaptées aux applications requises. Un prototype de guide d’onde et un prototype d’antenne ont été conçus, fabriqués et mesurés grâce à cette méthodologie. Les résultats obtenus démontrent l’intérêt, l'efficacité et le caractère général de la méthode proposée pour la conception de dispositifs hyperfréquences guidés à parois anisotropes. / In space applications, one of the biggest challenges is to reduce the size and mass of equipment, in order to reduce the costs of the rocket launch. For RF components, this has to be done without lowering RF performance (directivity, crosspolarization, single-mode bandwidth, etc.). The challenge is all the more problematic in the case of used horn antennas and waveguides because of their relatively large size. It has been shown that the use of anisotropic surfaces (i.e. corrugations and metamaterials) on the inside walls of guided RF structure makes it possible to influence and control the way electromagnetic waves travel, enabling new devices with radically different and improved performances : for waveguides, reduction of the cuto&# 64256; frequency ; for horn antennas, improvement of the directivity or a reduction of the side lobes. A state of the art of previous work done on metamaterial horn antennas pointed out that, even if the obtained and presented results seem very promising, the procedure to obtain the optimized RF structure is very time-consuming and requires considerable computer resources. The main contribution of this PhD work was to develop a new methodology based on the analytical Modal Expansion Theory (MET) for waveguides with anisotropic walls. This methodology makes it possible to optimize very rapidly the dimensions of the metamaterial surfaces adjusted to the required application. A metamaterial waveguide and antenna prototype have been designed, realized and measured thanks to this methodology. The results obtained demonstrate the usefulness, effectiveness and general applicability of the method developed for the design of RF structures with anisotropic walls.

Des propriétés électromagnétiques nouvelles peuvent être réalisées à l'aide d'une méta-surface à travers des structures artificielles. La permittivité et la perméabilité effectives d'une méta-surface peuvent être conçues de façon flexible et même accordées de sorte à présenter des réponses électromagnétiques pouvant être très différentes de celles de leurs homologues naturels, ce qui conduit à des propriétés améliorées voire parfois à un comportement extraordinaire. Cette thèse porte sur la conception, la fabrication et l'expérimentation de méta-surfaces micro-fluidiques pour le contrôle de propriétés des ondes électromagnétiques. Leur réalisation est basée sur des technologies relevant de la photolithographie et de la micro-fluidique, mises en œuvre sur des substrats souples d'épaisseur sub-longueur d'onde. Plus spécifiquement, nous avons exploité l'incorporation de divers matériaux dans un réseau de canaux micro-fluidiques, y compris des diélectriques liquides, un métal liquide et un métal solide pour manipuler davantage les réponses électromagnétiques des méta-surfaces correspondantes, telles que l'absorption, la transmission et la chiralité. La première partie de la thèse présente une méta-surface très absorbante sur une ultra-large bande spectrale et. Elle est constituée d'un réseau de résonateurs formés de gouttelettes d'eau noyées dans le matériau diélectrique souple, le PDMS; l’absorption mesurée est presque parfaite sur les bandes Ku, K et Ka. La seconde partie de la thèse porte sur un absorbeur agile et indépendant de l'angle dans la gamme Térahertz ; il s’agit d’une méta-surface à base de métal liquide, où un réseau de puits métalliques liquides dont la hauteur est contrôlée de façon continue, ce qui brise la limitation d'accordabilité dans le plan 2D. La troisième partie de la thèse porte sur une méta-surface chirale active. La méta-surface peut être commutée de achiral à chiral en déformant la structure en spirale initialement plane vers une géométrie 3D. Cette fonctionnalité peut manipuler la transmission hyperfréquence de symétrique à asymétrique sous incidence avant et arrière. En conclusion, l'optimisation de l'absorption, de la transmission et de la chiralité d’ondes électromagnétiques a été réalisée grâce à des méta-surfaces micro-fluidiques, qui semblent ainsi présenter un important potentiel applicatif dans divers domaines tels que la technologie furtive, l'imagerie et la communication optique / Novel and tailored electromagnetic properties can be realized using a metasurface through artificially designed structures. The effective permittivity and permeability of a metasurface can be flexibly designed and even tuned so as to exhibit electromagnetic responses that can be very different from those of their natural counterparts, leading to enhanced properties and sometimes to extra-ordinary behaviour. This thesis focuses on the design, fabrication and experimentation of meta-liquid-based metasurfaces for electromagnetic wave control and modulation. These metasurfaces are based on the use of both photolithography-based microfabrication and microfluidic technologies implemented onto thin and flexible substrates of sub-wavelength thickness. More specifically, the incorporation within a microfluidic channel network of various materials, including liquid dielectric material, liquid metal and solid metal have been exploited to further manipulate the electromagnetic responses of the related metasurfaces, such as the absorption, transmission and chirality. The first part of the thesis reports an ultra-broadband and wide-angle absorbing material by water-resonator-based metasurface. It consists of an array of water droplets embedded in the soft dielectric material, PDMS; it exhibited an almost perfect absorptivity over the Ku, K and Ka bands. The second part of the thesis focuses on a frequency-agile and wide-angle absorber in terahertz by liquid-metal-based metasurface, where a liquid-metal-pillar array can be continuously controlled in the vertical direction hence breaking the tuning limitation in the 2D plane. The third part of the thesis focuses on an active chiral metasurface. The metasurface can be switched from achiral to chiral by changing the spiral structure from planar pattern to 3D pattern. This functionality can manipulate the microwave transmission from symmetric to asymmetric under forward and backward incidence. In conclusion, tunability on the absorption, transmission and chirality have been realized through microfluidic metasurfaces, which appear having high potential applications in various areas such as stealth technology, imaging system, and optical communication, to name a few

abstract: The objective of this dissertation is to study the use of metamaterials as narrow-band and broadband selective absorbers for opto-thermal and solar thermal energy conversion. Narrow-band selective absorbers have applications such as plasmonic sensing and cancer treatment, while one of the main applications of selective metamaterials with broadband absorption is efficiently converting solar energy into heat as solar absorbers. This dissertation first discusses the use of gold nanowires as narrow-band selective metamaterial absorbers. An investigation into plasmonic localized heating indicated that film-coupled gold nanoparticles exhibit tunable selective absorption based on the size of the nanoparticles. By using anodized aluminum oxide templates, aluminum nanodisc narrow-band absorbers were fabricated. A metrology instrument to measure the reflectance and transmittance of micro-scale samples was also developed and used to measure the reflectance of the aluminum nanodisc absorbers (220 µm diameter area). Tuning of the resonance wavelengths of these absorbers can be achieved through changing their geometry. Broadband absorption can be achieved by using a combination of geometries for these metamaterials which would facilitate their use as solar absorbers. Recently, solar energy harvesting has become a topic of considerable research investigation due to it being an environmentally conscious alternative to fossil fuels. The next section discusses the steady-state temperature measurement of a lab-scale multilayer solar absorber, named metafilm. A lab-scale experimental setup is developed to characterize the solar thermal performance of selective solar absorbers. Under a concentration factor of 20.3 suns, a steady-state temperature of ~500 degrees Celsius was achieved for the metafilm compared to 375 degrees Celsius for a commercial black absorber under the same conditions. Thermal durability testing showed that the metafilm could withstand up to 700 degrees Celsius in vacuum conditions and up to 400 degrees Celsius in atmospheric conditions with little degradation of its optical and radiative properties. Moreover, cost analysis of the metafilm found it to cost significantly less ($2.22 per square meter) than commercial solar coatings ($5.41-100 per square meter). Finally, this dissertation concludes with recommendations for further studies like using these selective metamaterials and metafilms as absorbers and emitters and using the aluminum nanodiscs on glass as selective filters for photovoltaic cells to enhance solar thermophotovoltaic energy conversion. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2018

Este trabalho apresenta um novo formalismo bi-dimensional em diferenças finitas no domínio do tempo (2D-FDTD) para a simulação de estruturas baseadas em metamateriais. A natureza dispersiva destes meios é levada em consideração de forma precisa pela inclusão dos modelos materiais de Drude para os tensores permissividade elétrica e permeabilidade magnética. Todos os elementos dos tensores são considerados neste formalismo, o que o torna muito atraente para a modelagem de uma classe geral de estruturas eletromagnéticas. Dois efeitos de enorme impacto são analisados em detalhes, sendo eles a cobertura de invisibilidade e o rotacionamento de campo. Ambos os efeitos requerem a utilização de técnicas de transformação de coordenadas a qual deve ser aplicada apenas na região onde os campos eletromagnéticos precisam ser manipulados, tirando vantagem da invariância das equações de Maxwell quanto a estas operações. Esta técnica redefine localmente os parâmetros de permissividade e permeabilidade do meio transformado. O formalismo implementado apresentou grande estabilidade e precisão, uma conseqüência direta da natureza dispersiva dos modelos materiais de Drude, o que o caracteriza como uma boa contribuição para uma completa compreensão da fenomenologia por trás destes efeitos fascinantes. Os resultados numéricos apresentaram boa concordância com os disponíveis na literatura. Foi também observado que ambas estruturas são muito sensíveis a variações de freqüência do campo de excitação. / This work introduces an extended two-dimensional finite difference time domain method (2D-FDTD) for the simulation of metamaterial based structures. The dispersive nature of these media is accurately taken into account through the inclusion of the Drude material models for the permittivity and permeability tensors. All tensor elements are properly accounted for, making the formalism quite attractive for the modeling of a general class of electromagnetic structures. Two striking effects are investigated with the proposed model, namely, the invisibility cloaking and the field rotation effects. Both effects require the utilization of a coordinate transformation technique which must be applied only in the region where the electromagnetic field needs to be manipulated, taking advantage of the invariance of Maxwell\'s equations with respect to these operations. This technique locally redefines the permittivity and permeability parameters of the transformed media. The implemented formalism has proved to be quite stable and accurate, a direct consequence of the dispersive nature of the Drude material model, which characterizes it as a good contribution to fully understand the phenomenology behind these fascinating effects. The numerical results are in good agreement with those available in the literature. It was also verified that both structures are very sensitive to frequency variations of the excitation field.

Magnetic materials are one of the most interesting and promising class of materials for technological applications [1]. Among them, patterned ferromagnetic systems have an important role especially in the prospect of high density data storage [2], domain wall logic devices [3] and magnetic memory [4, 5]. Coupled systems of ferromagnetic and antiferromagnetic materials have been implemented to design sensors such as giant magnetoresistance (GMR) [6-8] and tunnel magnetoresistance (TMR) [9, 10]. Ferromagnetic nanoparticles have been used for the drug targeting, cancer therapy, MRI and many more applications [11, 12]. In addition, more recently, significant attention has been paid to explore the dynamic properties of magnetic materials in the GHz range and use them for technological applications such as microwave filters, signal processing, phase shifter, nonreciprocal microwave devices, spin wave guide, high frequency memory, logic elements [13-19] Boundary conditions, interactions between individual entities, and lateral confinement of magnetic charges generate diverse magnetic properties especially at nanoscale length [20, 21]. The variation of magnetic properties are even quite different when the size of the magnetic structure is smaller or comparable with the magnetic characteristic length such as mean free path of electron, width of domain wall and even the spin diffusion length [22-24]. In this study, we have considered different magnetic systems. Firstly, the multilayer of coupled ferromagnetic and antiferromagnetic system has been considered to evaluate the exchange bias anisotropy. [FeNi/IrMn]n multilayer systems with different thicknesses of ferromagnetic layer were studied. Static and dynamic properties were revealed through magnetometry measurements (VSM) and VNA-FMR techniques respectively. Angular variation of first order reversal curve (AFORC) and ferromagnetic resonance (AFMR) were performed to learn the intrinsic exchange bias distribution. Secondly, patterned magnetic structures were synthesized to understand the magnetization dynamics in confined geometry. Surface modulated thin films with different periodicity, dumbbell-shaped structures with variable size and three dimensional magnonic crystals have been studied using both static and dynamic measurement techniques. Micromagnetic simulations were performed to understand and explain the experimental results.

Afin de retrouver un paramètre efficace de la structure périodique, on s'est efforcé de développer la théorie de l'homogénéisation, qui considère la structure périodique comme un milieu homogène. Cette thèse porte principalement sur la proposition et la validation de l'homogénéisation classique et de second ordre. Une méthode d'homogénéisation est appliquée pour obtenir des paramètres efficaces de structures multicouches. De plus, une homogénéisation classique est adoptée pour calculer les propriétés de transmission de structures diélectriques multicouches et la relation de dispersion d'un réseau de cylindres métalliques monté sur un plan de masse métallique lisse. D'après cette relation de dispersion, la propriété de coupe-bande à une certaine bande de fréquences est découverte et est appliquée sur la reformation du diagramme de rayonnement de l'antenne à plaque traditionnelle en supprimant l'onde de surface propageant sur le plan de masse. Nous avons publié cette partie dans [22]. Nous démontrons expérimentalement une limitation importante de l'homogénéisation classique lors du calcul de la propriété de transmission d'un réseau métallique ultra-fin. Le coefficient de transmission mesuré est beaucoup plus faible que celui calculé par homogénéisation classique, bien que les interférences qui peuvent être causées par l'installation d’expérience imparfaite sont éliminées. Nous proposons donc une nouvelle homogénéisation de second ordre, qui permet d'obtenir le coefficient de transmission correspondant aux résultats numériques. De plus, l'homogénéisation de second ordre a été validée expérimentalement par plusieurs grilles métalliques de même dimension sauf l'épaisseur. / In order to retrieve effective parameter of the periodic structure, people have made effort to develop the theory of homogenization, which regards the periodic structure as a homo- geneous medium. This thesis mainly focuses on the proposition and validation of classical and second order homogenization. A kind of method for homogenization is applied to ob- tain effective parameters of multilayer structures. Moreover, classical homogenization is adopted to calculate transmission properties of dielectric multilayer structures and the dis- persion relation of metallic cylinder array mounted on a smooth metallic ground plane. From the dispersion relation, its band gap property at a certain frequency band is revealed and is applied to reshape the radiation pattern of traditional patch antenna by suppressing the surface wave propagating on the ground plane. We have published his part of the work in [22]. We experimentally demonstrate one important limitation of classical homogenization when calculating the transmission property of an ultra-thin metallic grating. The mea- sured transmission coefficient is much smaller than that calculated by classical homoge- nization, although the interferences may be caused by the imperfect experiment facility are eliminated. Thus we propose a new second order homogenization, which is able to get the transmission coefficient correspondent to numerical results. Furthermore, second order homogenization has been experimentally validated by several metallic grating with the same dimension except for the thickness. This part of work will be included in a chapter of a book will be published by Intech Publisher.

Cette thèse présente de nouveaux développements pour de petites antennes en cavité. L'objectif principal de la thèse est l'analyse de la performance de la bande passante de ces antennes pour des tailles d'ouverture qui sont petites par rapport à la longueur d'onde en espace libre. Des cavités de formes rectangulaires et circulaires intégrées dans un plan de masse infini et dans des plans de masse de dimensions latérales finies sont examinées en détail. Jusqu'à présent, dans la littérature, le choix pour ces antennes en cavités portait sur des antennes imprimées microruban (patch). L'objet de la thèse est de déterminer si les performances d'antennes en cavité de petite taille peuvent être améliorées et si oui, de quelle façon. A cet effet, nous avons tout d'abord étudié théoriquement, la limite supérieure de la bande passante pour cette configuration particulière en cavité. Nous en avons conclu que les antennes microruban intégrées dans une cavité n'atteignent pas la limite de la bande passante, ce qui est l'un des principaux résultats de la thèse. Les antennes intégrées dans une cavité avec un plan de masse infini ou fini sont ensuite analysées à l'aide de plusieurs modèles de ligne de transmission simples. Le deuxième résultat clé de la thèse un modèle de ligne de transmission spécifique et original qui montre que cette limite sur la bande passante est réellement atteignable. Par conséquent, ce modèle de ligne de transmission devient la base d'une nouvelle conception pour l'antenne en cavité. Enfin, le résultat le plus important de la thèse est la conception concrète de nouvelles antennes en cavité capables d'atteindre la performance maximale en bande passante. D'autres sujets sont abordés sont: i) la comparaison avec des structures à base d'éléments empilés en termes de bande passante, de facilité de fabrication et de coût, ii) l'extension de la limite grâce à l'inclusion de matériaux magnétiques idéaux et conducteurs magnétiques; iii) l'utilisation de la nouvelle structure d'antenne pour la constitution d'un réseau d'antennes compact; iv) les avantages de la nouvelle structure pour la réalisation d'antennes en cavité de tailles vraiment petites pour lesquelles les méthodes classiques ne permettent pas la réalisation d'antennes. / This thesis presents new developments in cavity type antennas. The main objective of the thesis is bandwidth performance analysis of antennas in cavities with aperture sizes which are small compared to the free space wavelength. Cavities of rectangular and circular shapes in an infinite and finite ground plane are investigated in detail. So far in the literature, microstrip patch antennas were the antenna of choice for cavity type antennas. The intention of the thesis is to determine if cavity type antennas can be improved and how. To this end, the bound on bandwidth for cavity antennas is investigated theoretically. It is concluded that patch antennas, in fact, do not reach the bound for cavity antennas, which is one of the key results of the thesis. Infinite and finite sized ground plane cavity antennas are further analyzed using several simple transmission line models. The second key result of the thesis is a demonstration that a special transmission line model corresponds to antennas that reach the bound on bandwidth. This transmission line model is the basis to a new cavity antenna design. Finally, the most important result is a practical, physical, design of novel cavity antennas capable of reaching the bandwidth bound. Furthermore, several additional topics are explored; i) A comparison with stacked patches design in terms of bandwidth, ease of fabrication, and cost; ii) The extension of the bound with the inclusion of ideal magnetic materials and magnetic conductors; iii) The new antenna design use in constructing a compact antenna array; iv) The benefits of the new design for constructing small cavity antennas previously not feasible with the classical design.

Over the past several decades our understanding and meticulous characterization of the transient and spatial properties of materials evolved rapidly. The results present an exciting field for discovery, and craft materials to control and reshape light that we are just beginning to fathom. State-of-the-art nano-deposition processes, for example, can be utilized to build stratified waveguides made of thin dielectric layers, which put together result in a material with effective abnormal dispersion. Moreover, materials once deemed well known are revealing astonishing properties, v.gr. chalcogenide glasses undergo an atomic reconfiguration when illuminated with electrons or photons, this ensues in a temporal modification of its permittivity and permeability which could be used to build new Photonic Integrated Circuits.. This work revolves around the characterization and model of heterogeneous and time-varying materials and their applications, revisits Maxwell's equations in the context of nonlinear space- and time-varying media, and based on it introduces a numerical scheme that can be used to model waves in this kind of media. Finally some interesting applications for light confinement and beam transformations are shown.

Many structural acoustic and vibration designs rely extensively on materials that are light-weight, stiff, and highly damped. Advanced materials such as metallic foams can be engineered to achieve these properties in order to control sound and vibration for a variety of aerospace, maritime, and ground transportation applications. In this work, the structural and acoustic properties of commercially available and digitally designed metallic foams are analyzed through numerical and experimental methods. Furthermore as a post-manufacturing process, metallic foams can be engineered in order to preferentially alter the microstructure and achieve material property enhancements. In this work, the following engineering methods are proposed and investigated: plastic deformation and material saturation. When a metallic foam is plastically deformed, the foam's porosity and pore shape are dramatically altered. This transformation in microstructure can lead directly to changes in bulk properties. In this work, a method for triaxial hydrostatic compression of metallic foams is proposed and demonstrated experimentally. The structural properties of transformed foams are tested using a load cell with digital image correlation. Transformed foams exhibit higher compliance, higher toughness, and a reduced Poisson ratio. Measurement and analysis of acoustic properties indicate that the transformed foams can absorb significantly more sound than the conventional samples of equal thickness in the test range of 0.25 - 4.50 kHz. Due to their open-cell microstructure, metallic foams can be filled with saturating materials. In this work, metallic foams saturated with viscous liquids are investigated for reducing vibration transmissibility in a structure. For the best performing saturated foam subject to a transient excitation, an order of magnitude increase in damping ratio is measured. Additionally, a composite foam (consisting of metallic foam saturated with polyurethane foam) is fabricated to enhance acoustic properties. For the best performing composite foam at normal incidence, the sound absorption coefficient is improved by a factor of 6 near 0.60 kHz and by a factor of 2 up to 4.5 kHz. Lastly, two methods for estimating acoustic absorption in metallic foams are presented which utilize finite element analysis and boundary layer theory. The proposed methods are discussed for commercially available foams as well as for representative digital designs. Limitations and assumptions of the methods pertaining to size scales and boundary layer features are addressed.

Nowadays, metamaterials have found their places in different branches of wave physics ranging from electromagnetics to acoustic waves. Acoustic metamaterials are sub-wavelength structures in which their effective acoustic properties are dominated by their structural shape rather than their constitutive materials. In recent years, acoustic metamaterials have gained increasing interest due to numerous promising applications such as sub-wavelength imaging, perfect absorption, acoustic cloaking, etc. The focus of the work herein is to leverage acoustic metamaterial/metasurface structures to manipulate the acoustic wavefront to pave the road for future applications of the metamaterials. In the first part of the work, the metamaterial structure is introduced, which can be leveraged for better manipulation of the transmitted wave by modulating both phase and amplitude. Initially, a general bound on the transmission phase/amplitude space for the case of arbitrary metasurface has been presented and subsequently, the necessary condition for the complete modulation of the transmitted wave is investigated. Next, a horn-like space coiling metamaterial is introduced, which satisfied the aforementioned condition and enabled us to simultaneously modulate both the phase and amplitude of the transmitted wave. Furthermore, our initial efforts toward designing a metamaterial capable of real-time phase modulation with relatively constant amplitude will be discussed. In the second part of this work, a novel metamaterial-based methodology is presented for the design of the air-permeable acoustic silencer. In this work, the concept of the bilayer-transverse metamaterial is introduced, and its functionality for silencing the acoustic wave is demonstrated. Furthermore, it is shown that the methodology presented herein essentially does not limit the ratio of the open area, and ultra-open metamaterial silencers may be designed. Eventually, based on the presented methodology, the ultra-open metamaterial featuring nearly 60% open area is designed, and silencing capacity of about 94% at the targeted frequency is experimentally realized. In the last part of this work, the behavior of a locally resonant class of acoustic metamaterial in the non-Rayleigh regime has been explored. Elaborately, it is demonstrated that in the case of spherical inclusion in a matrix material, large variation in the effective acoustic impedance emerges near the inclusion’s Eigenmode. Eventually, the potential application of this novel phenomenon in the non-destructive evaluation (NDE) and ultrasound imaging is discussed. / 2020-08-09T00:00:00Z