In recent years a new class of materials, the metamaterials, has emerged in the scientific community. The use of these materials makes possible to achieve unique electromagnetic properties, such as the negative refractive index. Today there exist several applications that take advantage of these special properties, such as sensors, antennas and invisibility cloaks, aiming at improving their intrinsic characteristics. Based on these considerations, this project aims at developing metamaterials structures to control the radiation properties of antennas in the microwave range, such as gain and directivity. More specifically, it was also chosen chiral metamaterials, mainly due to the phenomenon of electromagnetic field rotation which opens the possibility to control efficiently the radiation properties of antennas. In addition, chiral metamaterials, which have proved to be a more attractive alternative to obtain negative or zero refractive index, enable a greater degree of freedom in the design of different structures. This work encompasses all different phases of the structure design, namely: project, computational modeling, fabrication, and characterization of the proposed structures. We show improvements for the gain that in some cases reaches more than the double of the conventional monopole antenna gain and for the return loss parameter, which reaches minimum values. We also could maintain good efficiency and improve the input impedance matching. Finally, it is worth mentioning that this new technology also has the great potential to be applied in the telecommunication devices, particularly to improve communications based on antennas. / Nos últimos anos uma nova classe de materiais, os metamateriais, emergiu na comunidade científica. O uso desses materiais torna possível alcançar propriedades eletromagnéticas singulares, como o índice de refração negativo. Hoje existem vastas aplicações que usufruem destas propriedades especiais, como os sensores, mantas de invisibilidade e antenas, onde se procura o aperfeiçoamento de suas características intrínsecas. Com base nestas considerações, este projeto buscou desenvolver estruturas metamateriais para controle das propriedades de radiação de antenas na faixa de micro-ondas, tais como diretividade e ganho. Mais especificamente, foram utilizados os metamateriais quirais, principalmente devido ao fenômeno de rotação do campo eletromagnético que abre a possibilidade de controle mais eficiente das propriedades de radiação de antenas. Além disso, os metamateriais quirais, por se mostrarem uma alternativa mais atraente para se obter meios com índice de refração zero ou negativo, possibilitam um maior grau de liberdade no projeto de diferentes estruturas. Este trabalho contempla, ainda, todas as etapas de projeto de tais estruturas, quais sejam: projeto, modelagem computacional, fabricação, e caracterização das estruturas. Mostramos melhorias para o ganho que, em alguns casos, chega a mais do que o dobro do ganho da antena monopolo convencional e para o parâmetro de perda de retorno, que atinge valores mínimos. Nós também mantivemos uma boa eficiência e melhoramos o casamento de impedância de entrada. Finalmente, vale salientar que essa nova tecnologia também apresenta grande potencial de ser aplicada em dispositivos de telecomunicações, com o intuito de aprimorar a comunicação baseada em antenas.

In recent years a new class of materials, the metamaterials, has emerged in the scientific community. The use of these materials makes possible to achieve unique electromagnetic properties, such as the negative refractive index. Today there exist several applications that take advantage of these special properties, such as sensors, antennas and invisibility cloaks, aiming at improving their intrinsic characteristics. Based on these considerations, this project aims at developing metamaterials structures to control the radiation properties of antennas in the microwave range, such as gain and directivity. More specifically, it was also chosen chiral metamaterials, mainly due to the phenomenon of electromagnetic field rotation which opens the possibility to control efficiently the radiation properties of antennas. In addition, chiral metamaterials, which have proved to be a more attractive alternative to obtain negative or zero refractive index, enable a greater degree of freedom in the design of different structures. This work encompasses all different phases of the structure design, namely: project, computational modeling, fabrication, and characterization of the proposed structures. We show improvements for the gain that in some cases reaches more than the double of the conventional monopole antenna gain and for the return loss parameter, which reaches minimum values. We also could maintain good efficiency and improve the input impedance matching. Finally, it is worth mentioning that this new technology also has the great potential to be applied in the telecommunication devices, particularly to improve communications based on antennas. / Nos últimos anos uma nova classe de materiais, os metamateriais, emergiu na comunidade científica. O uso desses materiais torna possível alcançar propriedades eletromagnéticas singulares, como o índice de refração negativo. Hoje existem vastas aplicações que usufruem destas propriedades especiais, como os sensores, mantas de invisibilidade e antenas, onde se procura o aperfeiçoamento de suas características intrínsecas. Com base nestas considerações, este projeto buscou desenvolver estruturas metamateriais para controle das propriedades de radiação de antenas na faixa de micro-ondas, tais como diretividade e ganho. Mais especificamente, foram utilizados os metamateriais quirais, principalmente devido ao fenômeno de rotação do campo eletromagnético que abre a possibilidade de controle mais eficiente das propriedades de radiação de antenas. Além disso, os metamateriais quirais, por se mostrarem uma alternativa mais atraente para se obter meios com índice de refração zero ou negativo, possibilitam um maior grau de liberdade no projeto de diferentes estruturas. Este trabalho contempla, ainda, todas as etapas de projeto de tais estruturas, quais sejam: projeto, modelagem computacional, fabricação, e caracterização das estruturas. Mostramos melhorias para o ganho que, em alguns casos, chega a mais do que o dobro do ganho da antena monopolo convencional e para o parâmetro de perda de retorno, que atinge valores mínimos. Nós também mantivemos uma boa eficiência e melhoramos o casamento de impedância de entrada. Finalmente, vale salientar que essa nova tecnologia também apresenta grande potencial de ser aplicada em dispositivos de telecomunicações, com o intuito de aprimorar a comunicação baseada em antenas.

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<p>The advent of resonant metamaterials with strongly dispersive behavior allowed scientists to design new electromagnetic devices -- including (but not limited to) absorbers, antennas, lenses, holograms, and arguably the most well-known of them all, invisibility cloaks -- exhibiting properties that would otherwise be difficult to obtain. At the heart of these breakthrough designs is our ability to model the behavior of individual metamaterial elements as Lorentzian dipoles, and -- in applications that call for it -- collectively model an entire array of such elements as a homogenous medium with effective electromagnetic properties retrieved from measurements or simulations. </p><p>Of particular interest in the context of this dissertation is a certain type of metamaterials elements which -- while composed entirely of essentially non-magnetic materials -- respond to a magnetic field, can be modeled as magnetic dipoles, and are able to form a material with effective magnetic response. This thesis describes how such ``magnetic metamaterials'' have been utilized by the author when designing devices for applications in wireless power transfer (WPT) and computational imaging. For the former, I discuss in the thesis a metamaterial implementation of a magnetic `superlens' for wireless power transfer enhancements, and a magnetic reflector for near field shielding. For the latter I detail how we model the imaging capabilities of a recently-introduced class of dispersive metamaterial-based leaky apertures that produce pseudo-random measurement modes, and demonstration of novel Lorentzian-constrained holograms able to tailor their radiation patterns. </p><p>To design a magnetic superlens for WPT enhancements, we first demonstrate how an array comprising resonant metamaterial elements can act as an effective medium with negative permeability ($\mu$) and enhance near-field transmission of quasi-static non-resonant coil antennas. We implement a new technique to retrieve all diagonal components of our superlens' permeability, including its normal component, which standard techniques cannot retrieve. We study the effect of different components of the $\mu$ tensor on field enhancements using analytical solutions as well as 2D rotationally-symmetric full-wave simulations which approximate the lens as a disc of equal diameter, enabling highly efficient axisymmetric description of the problem. Our studies indicate enhancements are strongest when all three diagonal components of Re$(\mu)$ are negative, which we attribute to the excitation of surface waves.</p><p>The ability to retrieve permeability's normal component, awarded to us with the implementation of the aforementioned retrieval technique, directly enabled the design of a near field magnetic shield, which -- in contrast to the tripple-negative superlens -- relies on the normal component of $\mu$ assuming values near zero. The thesis discusses the theory behind this phenomenon and explains why such an anisotropic slab is capable of reflecting magnetic fields with component of their wave vector parallel to the slab's surface (fields which contain significant portions of the energy transferred in WPT systems with dipole-like coils). Furthermore, the dispersive nature of the resonant metamaterials used to realize the shield grants us the ability to block certain frequencies while allowing the transmission of other, which can be particularly useful in certain applications; conventional materials used for shielding or electromagnetic interference (EMI) suppression, on the other hand, block frequencies indiscriminately. </p><p>The thesis also discusses a single-pixel, metamaterial-based aperture we designed for computational imaging purposes. This aperture, termed \textit{metaimager}, forms pseudo-random radiation patterns that vary with frequency by leaking energy from a guided mode via a collection of randomly distributed resonant metamaterial elements. The metaimager, then, is able to interrogate a scene without any moving parts or expensive auxiliary hardware (both are common problems which plague synthetic aperture and phased array systems, respectively). While such a structure cannot be homogenized, when modeling its imaging capabilities we still rely on the fact each of its irises can be modeled analytically as a magnetic dipole using a relatively simple Lorentzian expression. Accurate qualitative modeling of such apertures is of paramount importance in the design and optimization stages, since it allows us to save time and money by avoiding prohibitively slow full-wave simulations of such complex structures and unnecessary fabrication processes. </p><p>Lastly, the thesis discusses how such an aperture can be viewed as a hologram in which pixels are realized by the metamaterial elements and the reference wave is realized by the fields that excite them. While the current metaimager implementation produces pseudo-random modes, the last section of the thesis discusses how, by accounting for the Lorentzian constraints of each pixel, a novel metamaterial hologram can be designed to yield tailored radiation patterns. An experiment utilizing a Fraunhofer hologram excited in a free-space illumination configuration indicates tailored modes can indeed be formed by carefully choosing the resonance frequency and location of each metamaterial. While this proof-of-concept example is relatively simple, more sophisticated realizations of such holograms can be explored in future works.</p> / Dissertation

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

This thesis presents the design of radio-frequency (RF) tunable active inductors (TAIs) with independent inductance (L) and quality factor (Q) tuning capability, and their application in the design of RF tunable phase shifters and directional couplers for wireless transceivers. The independent L and Q tuning is achieved using a modided gyrator-C architecture with an additional feedback element. A general framework is developed for this Q- enhancement technique making it applicable to any gyrator-C based TAI. The design of a 1.5V, grounded, 0.13um CMOS TAI is presented. The proposed circuit achieves a 0.8nH-11.7nH tuning range at 2GHz, with a peak-Q in excess of 100. Furthermore, printed and integrated versions of tunable positive/negative refractive index (PRI /NRI) phase shifters, are presented in this thesis. The printed phase shifters are comprised of a microstrip transmission-line (TL) loaded with varactors and TAIs, which, when tuned together, extends the phase tuning range and produces a low return loss. In contrast, the integrated phase shifters utilize lumped L-C sections in place of the TLs, which allows for a single MMIC implementation. Detailed experimental results are presented in the thesis. As an example, the printed design achieves a phase of -40 to +34 degrees at 2.5GHz. As another application for the TAI, a reconfigurable CMOS directional coupler is presented in this thesis. The proposed coupler allows electronic control over the coupling coefficient, and the operating frequency while insuring a low return loss and high isolation. Moreover, it allows switching between forward and backward operation. These features, combined together, would allow using the coupler as a duplexer to connect a transmitter and a receiver to a single antenna. Finally, a planar electronically steerable patch array is presented. The 4-element array uses the tunable PRI/NRI phase shifters to center its radiation about the broadside direction. This also minimizes the main beam squinting across the operating bandwidth. The feed network of the array uses impedance transformers, which allow identical interstage phase shifters. The proposed antenna array is capable of continuously steering its main beam from -27 to +22 degrees of the broadside direction with a gain of 8.4dBi at 2.4GHz.

Metasurfaces, introduced as a compact 2D alternative of metamaterials, have developed into a vast field in recent times for light manipulation at an ultra-compact scale. Metasurface applications have found a place in the literature for compact alternatives to lens, holograms, polarizers, color filters. Plasmonic metasurfaces consisting of noble metals such as gold and silver provide light confinement on an unprecedented scale. Gold and silver grown conventionally on transparent substrates are polycrystalline, and exhibit losses and limit performance of the device. Moreover, these materials have a lower damage threshold and melting point. To circumvent the lower melting point and damage thresholds, new materials, and material growing techniques need to be researched. <br>In the first part of this work, a metasurface for color holography with an epitaxially grown silver thin film on a transparent substrate is shown. The demonstrated metasurface has been the first ever epitaxial silver metasurface that operated in the transmission mode. This plasmonic hologram has also been the thinnest metasurface hologram operating in transmission mode at the time of its reporting. The holographic image of all three basic color components of red, green, and blue has been demonstrated in the transmission mode. The control of color has been achieved by resonant sub-wavelength slits and the phase can be manipulated through altering slit orientation. This amplitude and phase control pave the way to applications of ultra-compact polychromatic plasmonic metasurfaces for advanced light manipulation. In the second part, we explore temperature rise due to the optical absorption in plasmonic structures. Titanium Nitride based metasurfaces structures are fabricated, that work in harsh environmental conditions and high temperature. A time domain thermo reflectance technique for rapid measurement of temperature is explored. Finally, a practical design prototype for thermo-photovoltaic (TPV) emitters using plasmonic metasurfaces is fabricated and characterized.<br><br>

Dans cette thèse on étudie le comportement des ondes électromagnétiques lorsqu'elles rencontrent un matériau négatif, c'est-à-dire un matériau dont la permittivité électrique et/ou la perméabilité magnétique est négative. On se focalise ici sur le cas où seulement la permittivité change de signe. En dimension deux, les équations de Maxwell en régime harmonique se réduisent à deux sous-problèmes scalaires plus aisés à traiter. L'un de ces sous-problèmes autorise la propagation d'ondes de surface, appelées plasmons de surface, à l'interface entre le matériau négatif et le diélectrique, ce qui le rend particulièrement intéressant pour les applications. On se concentre sur ce sous-problème et en particulier sur sa partie principale qui correspond à une équation de conductivité. Cependant, comme la permittivité change de signe les outils classiques comme le Théorème de Lax-Milgram sont mis en défaut. Dans le premier chapitre, on introduit des outils utiles à la compréhension du reste de la thèse. On décrit en particulier comment l'étude l'équation de conductivité fait naturellement intervenir l'opérateur de Poincaré-Neumann dont le spectre encode les rapports de permittivité qui permettent l'existence des plasmons de surface. On présente une formulation intégrale et une formulation variationnelle de l'opérateur de Poincaré-Neumann et le lien qui existe entre ces deux formulations. Le second chapitre de ce manuscrit s'intéresse au caractère bien posé de l'équation de conductivité lorsque la permittivité change de signe. En utilisant des méthodes d'équations intégrales on propose une condition suffisante pour que ce problème soit bien posé. Dans le troisième chapitre de cette thèse, on se concentre sur le calcul numérique du spectre de l'opérateur de Poincaré-Neumann à l'aide des méthodes d'éléments finis. On s'intéresse à la convergence des valeurs propres calculées numériquement vers les valeurs propres théoriques. Dans le dernier chapitre, on étudie le problème de transmission des ondes électromagnétiques dans une couche métallique de permittivité négative sous l'angle des fonctions de Green. En particulier on s'intéresse au comportement de la fonction de Green pour ce problème lorsque l'épaisseur de la couche métallique tend vers zéro. / In this thesis, we study the behaviour of electromagnetic waves when interacting with a negative material. Such a material has a negative electric permittivity and/or magnetic permeability. Here we only focus on negative permittivity materials. In dimension two, Maxwell's equations in harmonic regime reduce to a couple of scalar, easier to tackle, sub-problems. One of these sub-problems allows surface waves to propagate along the interface between a negative material and a dielectric, which makes it very interesting for the applications. Such surface waves are called surface plasmons. Here, we focus on this sub-problem and more specifically on its main part which is a conductivity equation. Yet, as the permittivity sign changes between the negative material and the dielectric, it is not allowed to use the classical Lax-Milgram framework. In the first chapter, we introduce tools which are useful to understand the rest of this thesis. In particular, we describe how studying conductivity equation leads us to deal with the Poincar{'e}-Neumann operator. The spectrum of this operator encodes permittivity ratios that allow surface plasmons to propagate. We propose both the integral formulation and the variational formulation of this operator, and we explain the link existing in-between. In the second chapter of this thesis, we focus on the well-posedness property of the conductivity equation when permittivity sign changes. Using integral equation methods, we propose a sufficient well-posedness condition for this problem. In the third chapter, we deal with the numerical computation of the Poincaré-Neumann operator spectrum using finite element methods. We are interested in the convergence of numerically computed eigenvalues to the theoretical ones. In the last chapter, we study the electromagnetic wave transmission problem in a metallic layer with a negative permittivity from the Green's function point of view. In particular, we investigate the Green's function behaviour when the metallic layer thickness goes to zero.

Ce mémoire de thèse est consacré à l'étude, la fabrication et la caractérisation de métamatériaux en vue d'applications dans le domaine millimétrique et submillimétrique. Dans un premier temps, nous avons tenu à rappeler les propriétés remarquables ainsi que les processus physiques mis en jeux par cette nouvelle génération de matériaux. Le manuscrit regroupe essentiellement des résultats issus d’études réalisées sur différentes structures en microondes et en terahertz : métamatériaux composites, métamatériaux entièrement diélectriques à base de résonances de Mie, ouvertures sublongueur d’ondes basés sur la transmission extraordinaire assistée par plasmons de surface. Nos investigations ont permis d’ouvrir la voie à de multiples applications dans les domaines des capteurs et des télécommunications. / This PhD dissertation is dedicated to the study, fabrication and characterization of metamaterials for millimeter and submillimeter applications. First of all we proposed to remind the extraordinary properties and physical processes involving within this new generation of materials. The manuscript contains results obtained from studies performed on different categories of metamaterials at microwave and terahertz frequencies: composite metamaterials, all dielectric metamaterials based on Mie resonances, subwavelength apertures based on the extraordinary transmission assisted by surface Plasmon polaritons. Our investigations have contributed to open the path to multiple potential applications in the field of sensors and telecommunications.

Les métamatériaux sont des matériaux artificiels qui possèdent de nouvelles propriétés optiques grâce à leur structuration à l’échelle nanométrique. Un des principaux axes de recherche dans le domaine des métamatériaux s’intéresse aux indices de réfraction négatifs qui permettent la réalisation de lentilles « parfaites » ainsi que d’autres applications excitantes. Dans cette thèse, nous étudions théoriquement les propriétés de métamatériaux optiques de type « fishnet », en particulier l’origine de leur indice de réfraction négatif, ainsi que d’autres problèmes théoriques associés. La thèse peut être divisée en quatre parties.Dans la première partie, nous étudions la diffusion de la lumière à l’interface entre l’air et un métamatériau fishnet semi-infini. A l’aide d’une méthode numérique vectorielle, nous calculons les coefficients de diffusion de l’interface et nous démontrons que le transport de l’énergie est dû à un seul mode de Bloch, le mode fondamental du fishnet. Puis, en s’appuyant sur les coefficients de diffusion de l’interface et sur l’indice effectif de ce mode de Bloch, nous proposons un nouvel algorithme d’extraction des paramètres effectifs du métamatériau. Notre approche met l’accent sur le rôle clé joué par le mode de Bloch fondamental et elle permet d’extraire des paramètres effectifs plus stables que ceux obtenus avec les méthodes classiques basées sur le calcul de la réflexion et la transmission d’une couche de métamatériau d’épaisseur finie. Dans la deuxième partie, nous dérivons grâce à l’orthogonalité des modes de Bloch des expressions analytiques pour les coefficients de diffusion à l’interface entre deux milieux périodiques de périodes légèrement différentes. Nous montrons que les expressions analytiques permettent d’obtenir des résultats très précis pour différentes géométries allant de guides d’onde périodiques diélectriques à des métamatériaux métalliques. Ces expressions analytiques constituent donc un outil utile pour la conception et l’ingénierie de structures photoniques périodiques.Le mode de Bloch fondamental est central pour expliquer le phénomène de réfraction négative dans les métamatériaux fishnet. Dans la troisième partie, nous avons développé un modèle semi-analytique pour la constante de propagation complexe du mode de Bloch fondamental du fishnet. Le modèle est basé sur une analyse fine de la propagation et de la diffusion de la lumière à l’intérieur de la structure. Le modèle montre que l’origine des valeurs négatives de l’indice de réfraction sur une large bande spectrale peut être essentiellement comprise comme le résultat d’une résonance plasmonique dans les canaux transverses métal-insolant-métal du fishnet. La résonance plasmonique exalte la réponse « magnétique » du fishnet et les pertes associées à cette résonance peuvent être compensées en incluant du gain dans les couches diélectriques. En outre, le modèle simplifie l’ingénierie des paramètres géométriques des métamatériaux fishnet. C’est la résonance plasmonique dans des structures de type métal-isolant-métal (MIM) qui induit l’indice de réfraction négatif dans les métamatériaux de type fishnet. Dans la dernière partie, nous étudions le comportement asymptotique de nanorésonateurs MIM lorsque leur taille est réduite sous la limite de diffraction. En particulier, nous montrons que le facteur de qualité augmente d’un ordre de grandeur quand le volume du résonateur passe de (λ/2n)3 à (λ/50)3. Une étude complète est réalisée avec un modèle Fabry-Perot semi-analytique. Le modèle reste précis sur toute la gamme de tailles étudiées, même dans le régime quasi-statique où des effets de retard ne sont pas attendus. Ce résultat important et contre-intuitif indique que les résonances plasmoniques localisées dans des nanoparticules peuvent être comprises de la même manière que les résonances délocalisées dans des nanofils métalliques, c’est-à-dire comme des problèmes d’antennes basés sur des effets de retard. / Optical metamaterials are artificial media that exhibit new properties from structuring on the nanometric scale. One of the main researches in metamaterials investigates materials with negative refractive index, which can allow the development of perfect lens and other exciting potential applications. In this thesis, we theoretically study the properties of negative-index optical fishnet metamaterials, especially the origin of their negative-valued refractive index, and also associated theoretical problems. The thesis can be divided into 4 parts. In the first part we study the light scattering at an interface between air and a semi-infinite fishnet metamaterial. With a fully-vectorial numerical method, we calculate the scattering coefficients of the interface and find that the energy transport inside the fishnet is due to a single Bloch mode, the fundamental one. Based on the single-interface scattering coefficients and the effective index of this Bloch mode we propose a new algorithm for retrieving effective optical parameters of the metamaterial. The approach emphasizes the key role played by the fundamental Bloch mode and provides retrieved parameters that are more accurate or stable than those obtained by classical methods based only on light reflection and transmission through finite-thickness metamaterial slabs. Due to the importance of the fundamental Bloch mode in the light transport in metamaterials, in the second part, based on the Bloch mode orthogonality we derive closed-form expressions for the scattering coefficients at an interface between two periodic media with slightly different geometrical parameters, which is a computationally demanding electromagnetic problem. We show that the analytical expressions are very accurate for various geometries, including dielectric waveguides and metallic metamaterials. Thus they can be useful for designing and engineering stacks of periodic structures. As shown in the first part, the fundamental Bloch mode is central to explain the negative refraction phenomenon in fishnet metamaterials. In the third part, we derive an accurate semi-analytical model for the complex propagation constant of the fishnet fundamental Bloch mode. This is achieved by analyzing light propagation and scattering inside the fishnet. The model shows that the origin of broad-band negative index of fishnets can be mainly understood as a plasmon resonance in the transversal metal-insulator-metal (MIM) channels. The plasmon resonance enhances the ‘magnetic’ response of fishnet and the losses associated to this resonance can be compensated by including gain in the dielectric layers of the fishnet. Furthermore, the model allows an easy and precise geometrical tailoring of fishnet metamaterials. As shown in the third part, it is the plasmon resonance in metal-insulator-metal (MIM) structures that induces the negative index of fishnet metamaterials. In the last part, we study the asymptotic behavior of 3D MIM nanoresonators, as the resonator size is shrunk below the diffraction limit. In particular we show that the quality factor increases from 10 to 100 when the resonator volume is scaled down from (λ/2n)3 to (λ/50)3. We provide a comprehensive study with a semi-analytical Fabry-Perot model. The model remains accurate over the whole size scale even in the quasi-static regime for which retardation effects are not expected. This important and counterintuitive result indicates that both localized plasmon resonances in nanoparticles and delocalized resonance in elongated plasmonic nanowires can be possibly understood as a wave-retardation based antenna problem.