Metamaterials are humanly engineered artificial electromagnetic materials which produce electromagnetic properties that are unusual, yet can be observed readily in nature. These unconventional properties are not a result of the material composition but rather of the structure formed. The objective of this thesis is to investigate and design smaller and wideband metamaterial-inspired antennas for personal communication applications, especially for WiMAX, lower band and higher band WLAN applications. These antennas have been simulated using HFSS Structure Simulator and CST Microwave Studio software. The first design to be analysed is a low-profile metamaterial-inspired CPW-Fed monopole antenna for WLAN applications. The antenna is based on a simple strip loaded with a rectangular patch incorporating a zigzag E-shape metamaterial-inspired unit cell to enable miniaturization effect. Secondly, a physically compact, CSRR loaded monopole antenna with DGS has been proposed for WiMAX/WLAN operations. The introduction of CSRR induces frequency at lower WLAN 2.45 GHz band while the DGS has provided bandwidth enhancement in WiMAX and upper WLAN frequency bands, keeping the radiation pattern stable. The next class of antenna is a compact cloud-shaped monopole antenna consisting of a staircase-shaped DGS has been proposed for UWB operation ranges from 3.1 GHz to 10.6 GHz. The novel shaped antenna along with carefully designed DGS has resulted in a positive gain throughout the operational bandwidth. Finally, a quad-band, CPW-Fed metamaterial-inspired antenna with CRLH-TL and EBG is designed for multi-band: Satellite, LTE, WiMAX and WLAN.

[pt] Invisibilidade sempre mexeu com a imaginação de crianças e adultos. Quem nunca imaginou ser capaz de tornar-se invisível em certas ocasiões? Recentemente essa ideia da ficção científica tomou forma na vida real, e um dos objetivos do presente texto é explicar de uma maneira acessível as principais ideias físicas e matemáticas por trás do conceito de invisibilidade. Pedimos do leitor somente uma modesta familiaridade com Cálculo Vetorial, Séries de Fourier e Álgebra Linear. O objetivo da capa de invisibilidade é tornar um objeto não detectável por meio de energia eletromagnética. A capa é fisicamente realizada por um metamaterial especialmente projetado para redirecionar certas ondas eletromagnéticas irradiadas sobre o objeto. Nesta exposição, usaremos como exemplo a tomografia de impedância elétrica (TIE) como método de detecção e explicaremos como criar uma capa invisível à TIE. Cabe ressaltar que o processamento de imagem através da TIE diz respeito a um problema inverso e, no contexto das equações diferenciais, esse problema envolve, a partir de determinadas simplificações, a equação de Laplace com condições de contorno. Despretensiosamente, optamos pelo caso bidimensional para facilitar a exposição das idéias principais, embora todos os nossos resultados possam ser generalizados em 3 dimensões. / [en] Invisibility has always instigated children and adult s imagination. Who never thought of occasionally being able to turn yourself invisible? Recently, this science fiction idea has taken shape in real life, and one of the objectives of this text is explain the main physical and mathematical ideas behind the invisibility concept, on a comprehensible way. We only require the reader has a modest familiarity with Vectorial Calculus, Fourier Series and Linear Algebra. Invisibility cloak aims to turn an object imperceptible to electromagnetic energy detection. The cloak is made of an especially projected metamaterial that redirects certain electromagnetic waves irradiated over the object. Here we will take as an example electrical impedance tomography (EIT) as a detection method and we will explain how to create an invisible cloak for EIT. It is worth mentioning that image processing through EIT is an inverse problem. Thereby, in the context of differential equations, this problem involves a few simplifications in the Laplace s problem with contours conditions. Unpretentiously, we chose the two-dimensional case to simplify the exposition of the main ideas, although all of our results may be generalized in three-dimensional case.

Made available in DSpace on 2016-08-31T13:33:42Z (GMT). No. of bitstreams: 1 JoseLS_DISSERT.pdf: 2812015 bytes, checksum: 51363b9d128a3b11dbf78cdd5bf2f136 (MD5) Previous issue date: 2015-04-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work aims to characterize microstrip antennas operating on microwave bands, specifically on their behavior between 6 GHz and 16 GHz with metamaterial substrate. These microstrip antennas allow the miniaturization of their structures, which is important to devices that use this antenna, considering their features such: low cost, accommodation facility and structure lightness. In addition to the metamaterials, which are made by geometrical, structures from common materials, such conductors, dielectrics, magnetics or even their combination. The main characteristic of the metamaterials is based on presenting special features of permissiveness and permeability, which are not found in natural materials, whose main effect is the negative refraction rate. By having those features, it is possible to use them in many optical and electromagnetism ways. The metamaterial theory is described and applied on this work as a way of microstrip antenna substrate in order to work the permissiveness and permeability related to the scope of propagation of electromagnetic waves. Some analysis parameters are observed such: resonance and distant field frequency, formulating the characterization and behavior of the observed microstrip antennas / Este trabalho tem como objetivo caracterizar antenas de microfita operando na faixa de micro-ondas, especificamente o seu comportamento na faixa de frequência de 6 GHz a 16 GHz com substrato metamaterial. Essas antenas de microfita por sua vez, possibilitam a miniaturização de sua estrutura, o que tem sido importante para os dispositivos que fazem uso dessas antenas, pois possuem como propriedade: baixo custo, facilidade de acomodação e leveza em sua estrutura. Além dos metamateriais que são estruturas geométricas fabricadas a partir de materiais comuns, ou seja, materiais condutores, dielétricos, magnéticos ou através da combinação entre eles. A principal característica dos metamateriais baseia-se por apresentarem propriedades especiais de permissividade e permeabilidade não encontradas nos materiais em estado natural, cujo principal efeito é o índice negativo de refração. Por intermédio dessas características, permite sua aplicação em diversos meios em eletromagnetismo e óptica. A teoria do metamaterial é descrita e aplicada neste trabalho como forma de substrato de antenas de microfita visando trabalhar a permissividade e permeabilidade relativas no âmbito da propagação de ondas eletromagnéticas. São observados alguns parâmetros de análise, tais como: a frequência de ressonância e campos distantes, formulando a caracterização e comportamento das antenas de microfita estudadas

Made available in DSpace on 2014-12-17T14:55:19Z (GMT). No. of bitstreams: 1 MarinaldoPSN_TESE.pdf: 2731148 bytes, checksum: 7c2caa3355d4d42f0702baf0d147bf97 (MD5) Previous issue date: 2014-04-25 / Universidade Federal do Rio Grande do Norte / Metamaterials have attracted a great attention in recent years mostly due to their electromagnetic properties not found in nature. Since metamaterials began to be synthesized by the insertion of artificially manufactured inclusions in a medium specified host , it provides the researcher a broad collection of independent parameters such as the electromagnetic properties of the material host. In this work was presents an investigation of the unique properties of Split Ring Resonators and compounds metamaterials was performed. We presents a theoretical and numerical analysis , using the full-wave formalism by applying the Transverse Transmission Line - LTT method for the radiation characteristics of a rectangular microstrip antenna using metamaterial substrate, as is successfully demonstrated the practical use of these structures in antennas. We experimentally confirmed that composite metamaterial can improved the performance of the structures considered in this thesis / Os metamateriais tem atra?do uma grande aten??o nas ?ltimas d?cadas, principalmente devido as suas propriedades eletromagn?ticas n?o encontradas na natureza. Desde que os metamateriais passaram a ser sintetizados atrav?s da inser??o de inclus?es artificialmente fabricadas num meio hospedeiro especificado, isto propicia ao pesquisador uma larga cole??o de par?metros independentes, tais como as propriedades eletromagn?ticas do material hospedeiro. Neste trabalho foi realizada uma investiga??o das propriedades ?nicas dos Ressoadores em Anel Partido (Split Ring Ressonators - SRR) e dos metamateriais compostos. Apresentou-se uma an?lise te?rica e num?rico-computacional, utilizando o formalismo de onda completa atrav?s da aplica??o do m?todo da Linha de Transmiss?o Transversa LTT, para as caracter?sticas ressonantes de uma antena de microfita com patch retangular utilizando substrato metamaterial, assim como ? demonstrado com sucesso ? utiliza??o pr?tica dessas estruturas em antenas. Esta utiliza??o pr?tica ? confirmada experimentalmente

In dieser Dissertation wird eine allgemeine zweiskalige Homogenisierungsmethode für große Deformationen entwickelt, welche die Trägheitskräfte der Mikroskala konsistent berücksichtigt. Die energetische Skalenkopplung der Methode basiert auf der erweiterten Hill-Mandel Bedingung für Makrohomogenität. Darüber hinaus wird die kinematische Skalenkopplung diskutiert und eine Volumenintegrals-Verschiebungsbedingung aufgezeigt, die eine allgemeine dynamische Betrachtung ermöglicht. Um einen effizienten Algorithmus zu gewährleisten, werden vier makroskopischen Tangenten-Module in geschlossener Form hergeleitet. Es werden zwei Rechenbeispiele genutzt, um allgemeine Eigenschaften der Methode zu analysieren. Dazu gehören das makroskopische Konvergenzverhalten und die Übereinstimmung mit einskaligen Referenzsimulationen. Des Weiteren wird der Einfluss der Verschiebungsbedingung und die Wahl der Einheitszelle als representatives Volumenelement auf die Antwort der Makroskale untersucht. Der Fokus der Arbeit wird im Anschluss auf die Modellierung hochduktiler Betone (Engl.: Strain-Hardening Cementitious Composites – SHCC) unter Stoßbelastung gelegt. Zunächst wird anhand von experimentellen Daten ein vereinfachtes Materialmodell kalibriert, welches das homogenisierte Faserauszugsverhalten repräsentiert. Danach wird dieses Faserauszugsmodell auf der Mikroskale eingesetzt und mit der vorgestellten Homogenisierungsmethode untersucht. Schließlich wird ein Split-Hopkinson-Bar Zugversuch numerisch repliziert. Dieser wird verwendet um die Funktionaltät der Methode aufzuzeigen, wie dynamische Effekte des Materials und der Struktur untersucht werden können. / A general numerical two-scale homogenization method for large strains is developed, which consistently takes into account inertia forces at the microscale. The energetic scale coupling of the framework is based on the extended Hill-Mandel condition of macro-homogeneity. Furthermore, kinematic scale links are discussed and a volume integral displacement constraint is proposed. To enable an efficient algorithm, closed form formulations of four macroscopic tangent moduli are derived. These consistently include the microscale inertia effects as well as the proposed displacement constraint. Two numerical examples are presented, a layered microstructure and a locally resonant material. These examples are used to analyze general properties of the presented framework, namely the macroscopic convergence behavior and the overall match with single-scale reference calculations. In addition, both the displacement constraint and the choice of unit cell as representative volume element are studied with respect to their influence on the macroscopic response. Subsequently, the thesis focuses on the modeling of strain-hardening cementitious composites under impact loading. First, a simplified material model representing the homogenized fiber pullout behavior is calibrated using experimental data. Then, this fiber pullout model is used at the microscale and studied using the proposed dynamic homogenization framework. Finally, a split Hopkinson bar tension test is numerically replicated and used to showcase the ability of the framework to thoroughly study the dynamic effects of the material and structure.

[pt] Muitos drones subaquáticos (DSs) modernos usados no monitoramento militar e ambiental operam no oceano e são concebidos como transceptores intermediários entre sua estação base (EB) e redes de sensores sem fio subaquáticas (RSSFSs). Devido a salinidade e consequentemente a condutividade da água do mar, DSs não podem usar transmissões de rádio frequência (RF) convencionais, tanto para alimentar quanto para se comunicar com os nós sensores (NSs). Tentando superar essas limitações, sistemas de transmissão indutiva de energia (TIE) têm sido apontados como uma alternativa para RSSFSs assistidas por DSs confiáveis. TIE apresenta perdas menores do que técnicas de campo distante em meios complexos, mas é extremamente limitada em termos de distância de operação. Baseado nisso, a presente tese visa uma solução mais integrada para sistemas de monitoramento assistidos por DSs baseado em sistemas de TIE usando lentes e refletores de metamaterial (MTM) dedicados a aprimorar ambas a eficiência na transmissão de energia e a razão sinal-ruído dos dados transmitidos. Um novo modelo do canal magnético, baseado no modelo de linhas de transmissão magnéticas virtuais, incorporando os ganhos dos MTMs e as perdas da água do mar, também é apresentado de modo a facilitar a futura sistematização das RSSFSs. / [en] Most modern underwater drones (UDs) employed in military and environmental monitoring operate in the ocean and are conceived as intermediary transceivers between their base station (BS) and underwater wireless sensor networks (UWSNs). Due to the salinity and consequently the conductivity of seawater, UDs cannot use conventional radiofrequency (RF) transmissions, either for powering or communicating with the sensor nodes (SNs). Trying to overcome these limitations, inductive power transmission (IPT) systems have been pointed out as an alternative for reliable UD-assisted UWSNs. IPT presents lower losses than far-field-based techniques in complex media but is extremely limited in terms of operating distance. Based on that, the present thesis aims an all-integrated solution for UD-assisted monitoring systems based on IPT systems using metamaterial (MTM) lenses and reflectors dedicated to improving both the power transfer efficiency and the signal-noise ratio of the transmitted data. A new model of the magnetic channel, based on the virtual magnetic transmission line model, incorporating the MTM gains and the seawater losses, is also presented in order to facilitate the future systematization of UWSNs.

Metamaterials are humanly engineered artificial electromagnetic materials which produce electromagnetic properties that are unusual, yet can be observed readily in nature. These unconventional properties are not a result of the material composition but rather of the structure formed. The objective of this thesis is to investigate and design smaller and wideband metamaterial-inspired antennas for personal communication applications, especially for WiMAX, lower band and higher band WLAN applications. These antennas have been simulated using HFSS Structure Simulator and CST Microwave Studio software. The first design to be analysed is a low-profile metamaterial-inspired CPW-Fed monopole antenna for WLAN applications. The antenna is based on a simple strip loaded with a rectangular patch incorporating a zigzag E-shape metamaterial-inspired unit cell to enable miniaturization effect. Secondly, a physically compact, CSRR loaded monopole antenna with DGS has been proposed for WiMAX/WLAN operations. The introduction of CSRR induces frequency at lower WLAN 2.45 GHz band while the DGS has provided bandwidth enhancement in WiMAX and upper WLAN frequency bands, keeping the radiation pattern stable. The next class of antenna is a compact cloud-shaped monopole antenna consisting of a staircase-shaped DGS has been proposed for UWB operation ranges from 3.1 GHz to 10.6 GHz. The novel shaped antenna along with carefully designed DGS has resulted in a positive gain throughout the operational bandwidth. Finally, a quad-band, CPW-Fed metamaterial-inspired antenna with CRLH-TL and EBG is designed for multi-band: Satellite, LTE, WiMAX and WLAN.

Metallic nano-structures provide for new and exciting domains to investigate light-matter interactions. The coupling of these metallic nano-structures to semiconductor emitters allows for the observation of cavity QED effects including Purcell enhancement and Vacuum Rabi splitting. The focus of this dissertation will be to present an introduction and background to semiconductor optics, and metallic metamaterial systems. This will be followed by the presentation of the spectroscopy systems designed and constructed during my tenure as graduate student and the experimental data obtained with these systems. Some of the results have been published, while some of the presented material is still actively being pursued for publication. More specifically, the dissertation will cover the research at hand, experimental techniques, and results.

Metamaterials are artificially constructed "materials" which are formed from arrays of engineered elements. By designing individual elements as well as their interactions, the propagation of electromagnetic (EM) waves within the structure can be manipulated, so that new responses can be realised which may not be found in nature. The subject of this research concerns the study of miniaturised elements with strong EM responses so that the constructed metamaterial can better approximate an ordinary low-loss material. The research involves designing miniaturised magnetic resonators operating in the microwave frequency range. A novel resonator prototypes, so-called “helical resonators”, have been successfully designed and fabricated whose physical sizes can fall below 1% of the free space wavelength at resonance. This contributes to a size reduction of 90% compared with previously published work. In addition, an analytical model has been developed, so that the resonance parameters of a helical resonator have explicit expressions. In particular, a constant optimal metallic fill ratio is demonstrated to exist, which can achieve a minimum resonant frequency and a maximum miniaturisation for any given outmost dimension of the element. The accuracy of the model has been verified by both simulation and experiment. The frequency responses of fabricated helical elements were measured using a vector network analyser and a pair of small loop non- resonant dipole probes, and the parameters were extracted using the phase frequency fit method which proves to have the best accuracy and robustness. The properties of a regular square array of helical resonators are subsequently investigated, which can be regarded as a two-dimensional metamaterial. A relevant analytical model has been developed, which characterises the array as an equivalent sheet with surface current distributions, rather than an artificial medium with finite thickness. The relation between the macroscopic EM fields and the small scale properties of individual helical resonators are then established. In particular, the helical resonators are observed to be inherently chiral, thus the assembled interlocking array exhibits dichroism. The transmission coefficients for the circular EM waves with two different polarisation states have been derived, which have been verified by simulation and measurement results as well. In addition, it has been theoretically demonstrated that the resonator elements and their spacings can be engineered, so that the circular EM wave with one particular polarisation state can be totally attenuated around the element resonance, while the other state suffers negligible attenuation. A quadratic relation between the optimal array spacing and the elements’ quality factor has been demonstrated.

L’étude et la réalisation de métamatériaux auto-assemblés possédant une réponse magnétique aux fréquences optiques font l’objet d’un champ de recherche très actif depuis plusieurs années. De nombreux calculs théoriques ont prédit qu’un arrangement dense de briques élémentaires plasmoniques, « les méta-atomes », conduirait à des matériaux à indice négatif actifs dans le domaine du visible. Il a été démontré qu’un nano-objet ayant un coeur de silice décoré de 12 nanoparticules d’or sphériques permettrait d’optimiser le phénomène de magnétisme optique. Ma thèse repose sur l’élaboration de ces objets à partir de particules colloïdales, parfaitement symétriques, constituées d’un coeur de silice et 12 nodules de polystyrène. Ces nodules de PS pouvant être éliminés ultérieurement par dissolution. Ces objets ont permis de fabriquer des particules de silices décorées d’un nombre précis de « patchs » ou de « fossettes ». Ces objets ont été formés en grande quantité. Nous sommes parvenus à rendre les cavités de surface des particules à fossettes collantes pour des germes d’or de 2-3 nm de diamètre et initier leur croissance. Les mesures de propriétés optiques de ces dodécapodes dorés ont reflété le couplage intense existant entre les nanoparticules plasmoniques autour du coeur diélectrique. La possibilité de faire croitre de l’argent à la surface des germes d’or permet de générer des nanorésonateurs avec des modes magnétiques optiques encore plus intenses que ceux observés pour les systèmes à base d’or. / Over the last decade, the field of self-assembled metamaterials exhibiting unusual properties such as a magnetic response in the visible range represents a challenging and attracting area. Many simulations reported that a dense arrangement of specific plasmonic sub-units called “meta-atoms”, may lead to a material with a negative refractive index. It was reported by computational modelling that a dodecapod clusters made of a central dielectric core and surrounded by a controlled number of satellites (12 satellites, here) with a specific size can exhibited some interesting properties. Here, the purpose was to fabricate such clusters from colloidal particles, which are perfectly symmetrical, made of a silica core and 12 polystyrene nodules. Subsequently, those polystyrene nodules can be dissolved to get silica particles with a specific number of “patches” or “dimples”. Those objects were synthesized in a large quantity. We were able to make those dimples sticky to tiny gold seed of 2-3 nm size and to grow then for a specific size. Optical measurements reported the strong magnetic coupling in-between the plasmonic nanoparticles around the dielectric core. We also reported that growing silver on tiny gold seeds generates stronger magnetic responses than those observed from gold clusters.