Metamaterials are a growing area of interest in the electromagnetics community due to their highly uncommon wave-material interaction characteristics, and they can be modeled using transmission line (TL) based networks. From verification of negative refraction to modeling more complex devices such as invisibility cloaks and field rotators, TL metamaterials offer a tangible solution to modeling novel devices in 1-D, 2-D, and 3-D structures. While currently available TL metamaterials allow for a predictable and easily manufactured network, the need for periodic, regular grids make current TL metamaterials sub-optimal for devices with curved boundaries or realization on curved surfaces. Our work presents the theory and application of TL metamaterials on irregular, nonperiodic grids for modeling 2-D electromagnetic phenomena in TE polarization, allowing for accuracy in curved device boundary modeling and significantly increased adaptability in potential application to curved surfaces. Based on an irregular grid obtained using an unstructured surface mesher, irregularly-shaped individual cells are related to local medium parameters to represent an overall device. The design method is validated using simple scattering problems with known analytical solutions and simulation data through lumped-element circuit- network simulations. The design process is then applied to more complex devices such as the Luneburg lens and field rotator. Capabilities and limitations of this technique are tested and explored. A microstrip based version of this method is subsequently developed and investigated using circuit and full-wave simulation data as well as experiment of a printed-circuit realization.

In recent years, there has been an increasing interest on left handed metamaterials because of their possible innovative applications. The pioneer study introducing such materials was brought out by V. G. Veselago in 1968 [1]. In his work, Veselago proposed a medium having simultaneously negative electric permittivity and magnetic permeability and investigated its electromagnetic characteristics. He found out that the electric field, magnetic field and the propagation vector form a left handed triplet, thus named such materials as &ldquo / Left Handed Materials&rdquo / . Despite the significance of Veselago&rsquo / s inferences, the metamaterial theory stayed dormant for nearly 30 years. Towards the end of 1990s, the physically realizable left handed materials were built as the combination of two periodical structures / Split Ring Resonators (SRRs) and metallic thin wire arrays [4-5]. In this thesis, electrical and magnetic characteristics of the left handed metamaterials are theoretically investigated by using the analytical models for their permittivity and permeability functions with respect to frequency. For this purpose, first, two basic metamaterial structures / the Split Ring Resonators and Thin Metallic Wire Arrays are studied individually and their electrical and magnetic characteristics are examined. Finally, the composite left handed structure containing both SRRs and thin wires is studied to investigate the resulting simultaneous resonance properties and to estimate their overall effective permeability and permittivity functions.

This dissertation is focused on the design, fabrication, and characterization of novel metamaterials in microwave and terahertz regions with the following outcomes: A planar &micro / -negative metamaterial structure, called double-sided SRR (DSRR), is proposed in the first part of this study. DSRR combines the features of a conventional split ring resonator (SRR) and a broadside-coupled SRR (BC-SRR) to obtain much better miniaturization at microwave frequencies for a given physical cell size. In addition to DSRR, double-sided multiple SRR (DMSRR), double-sided spiral resonator (DSR), and double-sided U-spiral resonator (DUSR) have been shown to provide smaller electrical sizes than their single-sided versions under magnetic excitation. In the second part of this dissertation, a novel multi-band tunable metamaterial topology, called micro-split SRR (MSSRR), is proposed. In addition to that, a novel magnetic resonator structure named single loop resonator (SLR) is suggested to provide two separate magnetic resonance frequencies in addition to an electric resonance in microwave region. In the third part, two different frequency tunable metamaterial topologies called BC-SRR and gap-to-gap SRR are designed, fabricated and characterized at terahertz frequencies with electrical excitation for the first time. In those designs, frequency tuning based on variations in near field coupling is obtained by in-plane horizontal or vertical displacements of the two SRR layers. The values of frequency shifts obtained for these tunable metamaterial structures are reported to be the highest values obtained in literature so far. Finally, in the last part of this dissertation, novel double-sided metamaterial based sensor topologies are suggested and their feasibility studies are presented.

The optical properties of a concentric nanometer-sized spherical shell comprised of an (active) 3-level gain medium core and a surrounding plasmonic metal shell are investigated. Current research in optical metamaterials has demonstrated that including lossless plasmonic materials to achieve a negative permittivity in a nano-sized coated spherical particle can lead to novel optical properties such as resonant scattering as well as transparency or invisibility. However, in practice, plasmonic materials have high losses at optical frequencies. It will be demonstrated that a properly designed passive optical spherical core impregnated with a gain medium and coated with a concentric spherical plasmonic nano-shell will have a "super resonant" (SR) lasing state. The operating characteristics of this coated nano-particle (CNP) laser have been obtained numerically for a variety of configurations and will be reported here. Once the optical properties of the isolated active CNP inclusion are established, several examples of optical metamaterials using them as inclusions will be presented and analyzed. In particular, the effective material properties of these optical MTMs will be explored using effective medium theories that are applicable to a variety of inclusion configurations. Two-dimensional (2D) mono-layers of these active CNPs, which form metafilms; three-dimensional (3D) periodic arrays of these active CNPs; and 3D random distributions of these active CNPs will be described. The effective permittivities and refractive indexes of these optical MTMs will be compared and contrasted to those of their active CNP inclusions. In addition to the active MTMs, some examples of nano-photonic applications enabled by the unique properties of these inclusions will also be presented. Specifically metamaterial pigments derived from exploiting the high absorption and low scattering properties of the passive CNP particle will be explored for possible use in color display technology as well as the use of the SR lasing state and localized plasmon resonance of the active CNP for nano-sensing applications.

Novel metamaterial and metamaterial-inspired structures and microwave/antenna applications thereof are proposed and studied in this thesis. Motivated by the challenge of extending the applicability of metamaterial structures into practical microwave solutions, the underlying objective of this thesis has been the design of low-cost, easily fabricated and deployable metamaterial-related devices and the development of computational tools for the analysis of those. For this purpose, metamaterials composed of tightly coupled resonators are chosen for the synthesis of artificial transmission lines and enabling antenna applications. Specifically, fully-printed double spiral resonators are employed as modular elements for the design of tightly coupled resonators arrays. After thoroughly investigating the properties of such resonators, they are used for the synthesis of artificial lines in either grounded or non-grounded configurations. In the first case, the supported backward waves are exploited for the design of microstrip-based filtering/diplexing devices and series-fed antenna arrays. In the second case, the effective properties of such structures are employed for the design of a novel class of self-resonant, low-profile folded monopoles, exhibiting low mutual coupling and robust radiating properties. Such monopoles are, in turn, used for the synthesis of different sub-wavelength antenna arrays, such as superdirective arrays. Finally, an in-home periodic FDTD-based computational tool is developed and optimized for the efficient and rigorous analysis of planar, metamaterial-based, high-gain antennas.

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.

Metamaterials offer the freedom to tune the rich electromagnetic coupling between the constituent meta-atoms to tailor their collective electromagnetic response. Therefore, a comprehensive understanding of the nature of electromagnetic interactions between meta-atoms is necessary for novel metamaterial design, which is provided in the first part of this thesis. The subsequent work in the thesis applies the understanding from the first part to design and demonstrate novel one-dimensional metamaterials that overcome the limitations of metamaterials proposed in literature or exhibit electromagnetic responses not previously observed. Split-ring Resonators (SRRs) are a fundamental building block of many electromagnetic metamaterials. In the first part of the work in this thesis, it is shown that bianisotropic SRRs (with magneto-electric cross-polarisation) when in close proximity to each other, exhibit a rich coupling that involves both electric and magnetic interactions. The strength and nature of the coupling between two identical SRRs are studied experimentally and computationally as a function of their separation and relative orientation. The electric and magnetic couplings are characterised and it is found that, when SRRs are close enough to be in each other's near-field, the electric and magnetic couplings may either reinforce each other or act in opposition. At larger separations retardation effects become important. The findings on the electromagnetic interactions between bianisotropic resonators are next applied to developing a one-dimensional ultra-wideband backward-wave metamaterial waveguide. The key concept on which the metamaterial waveguide is built is electro-inductive wave propagation, which has emerged as an attractive solution for designing backward-wave supporting metamaterials. Stacked metasurfaces etched with complementary SRRs (CSRRs) have also been shown to exhibit a broadband negative dispersion. It is demonstrated through experiment and numerical modeling, that the operational bandwidth of a CSRR metamaterial waveguide can be improved by restricting the cross-polarisation effects in the constituent meta-atoms. The metamaterial waveguide constructed using the modified non-bianisotropic CSRRs are found to have a fractional bandwidth of 56.3\% which, based on a thorough search of relevant literature, is the broadest reported value for an electro-inductive metamaterial. A traditional coupled-dipole toy-model is presented as a tool to understand the field interactions in CSRR based metamaterials, and to explain the origin of their negative dispersion response. This metamaterial waveguide should be of assistance in the design of broadband backward-wave metamaterial devices, with enhanced electro-inductive waveguiding effects. In the final part of the thesis, a one-dimensional metamaterial prototype that permits simultaneous forward- and backward-wave propagation is designed. Such a metamaterial waveguide could act as a microwave analogue of nanoparticle chains that support electromagnetic energy transfer with a positive or a negative dispersion due to the excitation of their longitudinal or transverse dipole modes. The symmetry of the designed hybrid meta-atom permits the co-existence of two non-interfering resonances closely separated in frequency. It is experimentally and computationally shown that the metamaterial waveguide supports simultaneous non-interacting forward- and backward-wave propagation in an overlapping frequency band. The proposed metamaterial design should be suitable for realising bidirectional wireless power transfer applications.

We study theoretically graphene-like plasmonic metamaterials, in particular a honeycomb structured array of identical metallic nanoparticles, and examine the collective plasmonic modes that arise due to the near-field dipolar coupling between the localised surface plasmons of each individual nanoparticle. An analysis of the band structure of these eigenmodes reveals a phenomenal tunability granted by the polarisation of the dipole moments associated with the localised surface plasmons. As a function of the dipole orientation we uncover a rich phase diagram of gapped and gapless phases, where remarkably every gapless phase is characterised by the existence of collective plasmons that behave as massless chiral Dirac particles, in analogy to electrons in graphene. We consider lattices beyond the perfect honeycomb structure in two ways. Firstly, we break the inversion symmetry which leads to collective plasmons described as massive chiral modes with an energy dependent Berry phase. Secondly, we break the three-fold rotational symmetry and investigate generic bipartite lattices. In this scenario we progressively shift one sublattice away from the original honeycomb arrangement and observe a sequence of topological phase transitions in the phase diagram, as well as the merging and annihilation of Dirac points in the dispersions. After examining the purely plasmonic response we wish to address the true eigenmodes responsible for transporting electromagnetic radiation. For this reason we examine plasmon polaritons that arise from the strong light-matter coupling between the collective plasmons in a honeycomb array of metallic nanoparticles and the fundamental photonic mode of an enclosing cavity. Here we identify that the Dirac point remains robust and fixed in momentum space, irrespective of the light-matter coupling strength. Moreover, we demonstrate a qualitative modification of the polariton properties through modulation of the photonic environment, including order-of-magnitude renormalisation of the group velocity and the intriguing ability to invert the chirality of Dirac polaritons.

L’optimisation offre la possibilité, dans de nombreux domaines, d’améliorer les performances d’unsystème donné, qu’il soit physique ou mathématique. Depuis quelques décennies, les méthodesd’optimisation metaheuristiques ont fait leurs preuves, notamment dans le domaine de la mécanique.Du grec meta signifiant "un niveau au dessus", les metaheuristiques permettent de s’affranchir ducalcul des sensibilités souvent problématique quant à la résolution de problèmes d’optimisationcomplexes et/ou NP difficiles. En outre, elles ont la capacité à analyser simultanément l’ensemble dudomaine des solutions, ce qui leur permet converger efficacement vers l’optimum global de la fonctionobjectif considérée. Notre travail propose le développement d’une nouvelle méthode metaheuristiqueintelligente, basée conjointement sur l’algorithme d’optimisation par essaim particulaire PSO, etl’algorithme PageRank développé par MM. Brin et Page, et utilisé par le moteur de rechercheGoogle. Cet algorithme, appelé Inverse-PageRank-PSO (I-PR-PSO), a été validé sur un benchmarkde fonctions mathématiques, puis en optimisation contrainte sur des treillis mécaniques. Interfacéeavec l’algorithme Evolutionary Structural Optimization (ESO), elle a été adaptée à l’optimisationtopologique et a permis de trouver des résultats dont les topologies sont régulières et les temps decalcul minimisés. Dans le domaine des metamatériaux, nous avons développé une cape d’invisibilitéélectromagnétique fréquentielle, c’est à dire un metamatériau dont les parties réelle et imaginaire dela perméabilité effective sont négatives. En appliquant notre algorithme I-PR-PSO aux metamatériauxmécaniques, nous avons montré qu’il est possible de développer un metamatériau constitué d’acierqui présente des grandes déformations à l’échelle macroscopique, dues notamment aux grandsdéplacements présents dans le Volume Elémentaire Représentatif à l’échelle microscopique. / Based on a recent research concerning the PageRank algorithm used by the famous search engineGoogle, a new Inverse-PageRank-Particle Swarm Optimizer (I-PR-PSO) is developed, in order toimprove the performances of classic PSO. After having been tested and validated on a benchmarkof classical mathematical functions, this algorithm has been validated on constrained optimization,applied on classical trusses of the literature. Interfaced with the Evolutionary Structural Optimizationalgorithm, this algorithm has shown its performances on topology optimization, applied to structuralmechanics. Finally, using the performances of our newly developed algorithm, we have developedmetamaterials. In electromagnetics, a frequantial cloaking device has been developed, minimizingthe effective permeability of the considered Representative Volume Element. In mechanics, we havedeveloped a metamaterial made of steel which exhibits hyper-elastic - or, at least, non linear -mechanical behaviour. Combining great displacements and rotations at microscale, the developedmetamaterial exhibits great deformations at the macroscale as well.

La identificació per radiofreqüència (RFID) és una tecnologia de comunicació sense fils entre un lector i un transductor anomenat etiqueta, que s’adhereix als objectes per a identificar-los o emmagatzemar-ne informació. A diferència dels seus predecessors, els codis de barres òptics, l’enllaç de comunicació no requereix visió directe i es poden llegir múltiples etiquetes al mateix instant de temps. El rang d’operació és significativament superior també. Totes aquestes característiques afavoreixen el desenvolupament del que serà, segons els experts, la revolució de la Internet de les Coses, que permetrà identificar qualsevol objecte etiquetat des de qualsevol ordinador, instantàniament. Només dos factors impedeixen el desenvolupament i expansió de la tecnologia RFID: la falta d’uniformitat en la estandardització i els costos dels sistemes RFID, que van disminuint ràpidament any rere any. La finalitat de la tesi és abordar i aportar solucions a la falta d’homogeneïtat en els estàndards de RFID en el rang de freqüències ultra altes (UHF). L’objectiu, per tant, es centra en dissenyar etiquetes RFID per operar en les bandes de freqüència de les diferents regions del món. És a dir, es dissenyaran etiquetes RFID duals en freqüència per operar en diferents regions. Per aconseguir aquesta fita es desenvolupa un mètode pertorbatiu mitjançant les línies de transmissió artificials de tipus ressonant, basades en conceptes metamaterial. Aquestes línies permeten cert control dels paràmetres elèctrics de les xarxes d’adaptació que es concatenaran entre l’antena i el xip de l’etiqueta RFID. Així, aprofitant les característiques de controlabilitat dels metamaterials, s’implementen etiquetes RFID multibanda. L’estudi analític del mètode pertorbatiu, així com el disseny, fabricació i mesura de les etiquetes RFID són els blocs principals d’aquest treball. / Radiofrequency identification (RFID) is a wireless communication technology, consisting on a link between a reader and a transducer namely tag. The tag is attached to the objects in order to identifier them and to provide information of such objects. RFID is being developed to replace the optical bar codes, because it offers some relevant advantages as the possibility to read multiples tags at the same time without direct line of sight. It also involves that the RFID read ranges are largest. According to experts, the RFID technology will allow to develop the revolution of The Internet of Things, which can identifier any tagged object from any computer, instantly. However there are two factors which hinder the development and expansion of RFID technology: the standard (lack of uniformity) and the costs associated to RFID systems, which are decreasing year after year. The thesis goal deals with solutions to solve the lack of uniformity of the standard in the RFID ultra-high frequencies (UHF).Therefore, the thesis aim consists in designing RFID tags capable to operate at two frequency bands of the different worldwide regions. In order to achieve this target a perturbation method has been carried out by means of the resonant-type artificial transmission lines, based in metamaterial concepts. Such lines can engineer and tailor the dispersion diagram and characteristic impedance (to some extend) of the impedance matching networks, which are cascaded between the antenna and the chip of the tag. Then, it is possible to implement multiband RFID tags, thanks to the metamaterial controllability. This work has compiled the analytical study of the perturbation method, and also the design, fabrication and measure of the RFID tags.