Thèses sur le sujet « METAMATERIA »
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Ni, Sisi (Sisi Sophie). « Phononic metamaterials based on complex geometries : "a new kind of metamaterial" ». Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/89957.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Facing the growing challenges of energy, environment, security and disease treatment, the demand for novel materials are growing. While the material centric approach have resulted in development of new materials for advanced applications, we introduce a geometric approach as a complementary point of view for further innovation in this ever expanding and growing field. Inspired by the ubiquitous fractals-like geometry of in natures, the scale transformation (i.e. dilation or contraction) is included in the framework since fractal geometries shows structures at all scales (usually discrete and finite in physical world). We developed our framework using metamaterials since it enable us to design "atoms" or "molecules" and their relative arrangement with greater freedom (i.e. not limited by the chemical bond or ionic bond in classical materials system). We studied metamaterials using prefractals from both exact-self similar fractal and random fractal samples. For exact-self similar fractals, we choose H tree based prefractals and Hilbert Curve prefractals bounded system given their unique geometric properties and wide applications. Guided by the framework, we investigated several key parameters (e.g. level of iteration, geometric anisotropy, impedance contrast, arrangement of subunit, resolution) that would dictate the dispersion behavior of the system. It was found that for exact-self similar prefractals, multiple spectrum bandgaps (i.e. broadband response) can be achieved with increased level of iterations where translation symmetry is imposed through boundary condition. Furthermore, the transition from scale dependence and independent described by the general framework has been observed for all the samples we studied. Furthermore, for single prefractal resonator, subwavelength (~1/75[lambda]) behavior has been observed and explained using a simple analytical model. For metamaterials based on fractional Brownian motion, the Hurst constant is found to be a good indicator of phononic behavior of the system, besides other parameters studied. Our findings does not only expand the repertoire for novel materials by introducing the ubiquitous yet unconventional geometry to metamaterials; but also have interdisciplinary applications in biology, seismology, arts, hence shine lights on our understanding of nature.
by Sisi (Sophie) Ni.
Ph. D.
2
Macêdo, Jorge Andrey da Silva. « Formalismo FDTD para a modelagem de meios dispersivos apresentando anisotropia biaxial ». Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/18/18155/tde-15102008-135510/.
Texte intégralRésumé :
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.
3
Martínek, Luděk. « Antény s kryty z metamateriálů ». Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-219978.
Texte intégralRésumé :
This thesis deals with microstrip antennas covered by the metamaterials. First, are described planar antennas, their problems and the emergence of surface waves. Surface waves can cause unwanted coupling among particular parts of the structure and can degrade its parameters. The problem can be solved using an electromagnetic band gap structure (EBG). These periodic structures are able to suppress surface waves in different frequency bands. It is shown how the EBG structure in the function superstate improve directivity and antenna gain. Radiation conventional microstrip antenna with metallo-dielectric EBG superstrate and with the purely dielectric double-layer superstrate is described. The both structures are designed and simulated in CST Microwave Studio program. Further is described the antenna radiation with so-called mushroom structure and metallo-dielectric EBG superstate. The structure is again designed and simulated in CST MWS program. Finally, there are two structures with metallo-dielectric superstate implemented and measured.
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Sartori, Eduardo Jose. « Metodologia experimental de desenvolvimento de grades metamateriais com permissividade quase-zero e negativa ». [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260806.
Texte intégralRésumé :
Orientador: Hugo E. Hernandez FigueroaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
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Resumo: Metamateriais são estruturas ou arranjos geométricos feitos a partir de materiais comuns, dielétricos, condutores, magnéticos ou por combinação destes. Os metamateriais caracterizam-se principalmente por apresentarem propriedades especiais de permissividade ( e) e permeabilidade ( µ) não encontradas nos materiais em estado natural, cujo principal efeito é o índice negativo de refração (n < 0). Essas características permitem seu emprego em diversos tipos de aplicações em eletromagnetismo e óptica, tais como filtros passa-faixa e rejeita-faixa, espelhos dielétricos, super lentes etc. Normalmente, o equacionamento envolvido no cálculo de parâmetros dos metamateriais são complexos e, na maioria das vezes, necessitam de apoio computacional. Por este motivo, o presente trabalho traz um estudo experimental sobre dois tipos de comportamento metamaterial, o de permissividade quase-zero e negativa, analisando seu desempenho sob vários aspectos geométricos e de características dos materiais envolvidos, além de propor uma metodologia de desenvolvimento, a qual possibilita um rápido dimensionamento de diversos tipos de grades metamateriais, baseada em cálculos simples ou consulta direta a tabelas e curvas de projeto.
Abstract: Metamaterials are structures or geometric arrangements made from common materials, dielectrics, conductors, magnetic or a combination of these. Metamaterials are characterized mainly because of their special characteristics of permittivity ( e) and permeability ( µ), not found in the materials at natural state, whose main effect is the negative index of refraction (n <0). These characteristics allow its use in several types of applications in electromagnetism and optics, such as band-pass and band-stop filters, dielectric mirrors, super lenses etc.. Typically, the equations involved in the calculation of parameters of metamaterials are complex and, in most cases, require high capability computational methods. For this reason, this work presents an experimental study on two types of metamaterial behavior, near-zero and negative permittivity, examining its performance in several geometric aspects and characteristics of the materials involved, and propose a development methodology, which allows a fast scaling of various types of metamaterials grids, based on simple calculations or direct consultation tables and curves design.
Doutorado
Telecomunicações e Telemática
Doutor em Engenharia Elétrica
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Strikwerda, Andrew. « Metamaterial enhanced coupling ». Thesis, Boston University, 2012. https://hdl.handle.net/2144/31611.
Texte intégralRésumé :
Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
In the past decade interest in metamaterials has risen dramatically. This is due, in large part, to metamaterials' ability to exhibit electromagnetic behavior not normally found in nature. This is because these artificial structures display a strong electromagnetic response as a result of their geometry, as opposed to their chemistry, and that response typically dominates that of the substrate they are placed on. As a result, metamaterials can couple free space radiation in previously unheard of ways, and in this thesis I examine several of these coupling mechanisms. After an appropriate discussion of theoretical and experimental tools required for metamaterial study, the thesis turns to the metamaterial substrate and explores the coupling effects of the metamaterial and the substrate itself. We discuss the theory and experimentally demonstrate that the metamaterial and substrate composite can couple free space radiation for use in enhanced dielectric sensing, perfect absorption, and even mechanical deflection for electromagnetic detection. In addition to coupling with dielectric materials, the near field response of a metamaterial can also couple with another metamaterial. Subsequently, this thesis investigates the coupling between a pair of identical split ring resonators, and develops a general framework for evaluating the mode hybridization that results from their near field interaction. In fact, we find that the near field coupling is extremely sensitive to the relative orientation of the two metamaterials, and results in mode splitting between the two resonators. By manipulating their lateral displacement, the coupling, and the mode splitting, can be altered. In this way, an unprecedented modulation of the metamaterial response is demonstrated. Finally, we turn our attention to the effects that metamaterial behavior has on the far field response. Specifically, we focus on the symmetry, or lack thereof, of the unit cell and show that it manifests itself as a birefringence in the far field. As a result, metamaterials can be used as wave retarders to couple between polarization states. Herein we analyze this behavior and experimentally demonstrate functioning metamaterial based terahertz waveplates that are highly efficient at a previously unachieved sub wavelength size.
2031-01-01
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Li, Lianbo. « Metamaterial based superdirectivity ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:65f10679-cbf2-4c86-897e-8121225c44eb.
Texte intégralRésumé :
A model-supporting, simple, compact, robust and high efficiency two- element parasitic superdirective array comprising electrically small reso- nant metamaterial elements, namely singly split resonator rings (SSRRs), is predicted by an analytical model and is verified by CST simulation re- sults. The analytical model is built by combining a method of calculating a two-SSRR array's far fild radiated energy density and a well working equivalent circuit for a two-SSRR parasitic array. This model is capable of easily but accurately predicting the far field radiation behaviours of an electrically small parasitic array of two SSRRs (the two SSRRs are not necessarily standard and identical), based on certain information of the array, namely the SSRRs' dimensions, the SSRRs' electrical components (L, C and R), the SSRRs' rotating orientation angles (α1 and α2), the two SSRRs's separation (d) and the array's operation frequency. The impor- tance of this analytical model in designing parasitic superdirective arrays is discussed. Simulation results show that the model predicted two-SSRR parasitic superdirective structure (the `CC' structure) can achieve an end- fire directivity of 4.36, with an elements' separation d = 4mm working at 1:914GHz, and can maintain an efficiencyciency as high as 98:6%. After a short discussion of the design principle behind the `CC' structure, improved su- perdirective structures of are identified and studied based on simulation results. Among these structures, the 'CCLr' structure can achieve the largest directivity value of 5.06 (very close to 5.25, the theoretical limit value of a two-dipole array) with a moderate efficiency of 81:4%. A com- parison between these two-SSRR parasitic superdirective structures (the `CC' and its improved versions) and two commercial two-element Yagi an- tennas show that these two-SSRR structures achieve better directive per- formances than the commercial two-element Yagi antennas do. Through performing the study of near field energy ow for magnetic dipole based structures (analytical results) and SSRR based structures (simulation re- sults), with the help of the concept of causal surfaces, the physical reason behind the superdirectivity phenomenon is revealed.
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Shepard, III Ralph Hamilton. « Metamaterial Lens Design ». Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/194734.
Texte intégralRésumé :
Developments in nanotechnology and material science have produced optical materials with astonishing properties. Theory and experimentation have demonstrated that, among other properties, the law of refraction is reversed at an interface between a naturally occurring material and these so-called metamaterials. As the technology advances metamaterials have the potential to vastly impact the field of optical science.In this study we provide a foundation for future work in the area of geometric optics and lens design with metamaterials. The concept of negative refraction is extended to derive a comprehensive set of first-order imaging principles as well as an exhaustive aberration theory to 4th order. Results demonstrate congruence with the classical theory; however, negative refraction introduces a host of novel properties. In terms of aberration theory, metamaterials present the lens designer with increased flexibility. A singlet can be bent to produce either positive or negative spherical aberration (regardless of its focal length), its contribution to coma can become independent of its conjugate factor, and its field curvature takes on the opposite sign of its focal power. This is shown to be advantageous in some designs such as a finite conjugate relay lens; however, in a wider field of view landscape lens we demonstrate a metamaterial's aberration properties may be detrimental.This study presents the first comprehensive investigation of metamaterial lenses using industry standard lens design software. A formal design study evaluates the performance of doublet and triplet lenses operating at F/5 with a 100 mm focal length, a 20° half field of view, and specific geometric constraints. Computer aided optimization and performance evaluation provide experimental controls to remove designer-induced bias from the results. Positive-index lenses provide benchmarks for comparison to metamaterial systems subjected to identical design constraints. We find that idiosyncrasies in a metamaterial lens' aberration content can be exploited to produce imaging systems that are superior to their conventional counterparts. However, in some circumstances the reduced low-order aberration content in a metamaterial lens reduces the effectiveness of aberration balancing and stop shifting. Through a series of design experiments the relative advantages and challenges of using metamaterials in lens design are revealed.
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Ekmekci, Evren. « Design, Fabrication And Characterization Of Novel Metamaterials In Microwave And Terahertz Regions : Multi-band, Frequency-tunable And Miniaturized Structures ». Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612730/index.pdf.
Texte intégralRésumé :
This dissertation is focused on the design, fabrication, and characterization of novel metamaterials in microwave and terahertz regions with the following outcomes:
A planar µ-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.
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Tan, Szu Hau. « Metamaterial for Radar Frequencies ». Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/17465.
Texte intégralRésumé :
Approved for public release; distribution is unlimitedThe objective of this thesis is to investigate a new design of periodic metamaterial (MTM) structure for radar cross-section (RCS) reduction application on aircraft and ships. MTMs are man-made materials, not found in nature, that exhibit unusual properties in the radio-, electromagnetic-, and optical-wave bands. The cells of these periodic MTM structures must be much smaller than the wavelength of the frequency of interest. In a MTM, the structure and dimensions of the design at the frequency of interest can produce negative values of permeability and/or permittivity, which define the electrical properties of the MTM. This study looks at various designs of absorbing layers presented in technical papers and verifies the results in simulations. Modifications are done to the existing designs to achieve good absorption level at the radar-frequency band of interest. Modeling and simulation are done in Microwave Studio by Computer Simulation Technology (CST). The S-parameters S11 (reflection coefficient) and S12 (transmission coefficient) are used to investigate the performance of the MTM as a radar-frequency absorber.
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Demetriadou, Angela. « Studies of metamaterial structures ». Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/11396.
Texte intégral
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Le-Van, Quynh. « Optoelectronic Metamaterials ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS082/document.
Texte intégralRésumé :
Une nouvelle génération de dispositifs électroniques et optoélectroniques combinant hautes performances et bas coût se profile grâce aux promesses des films à boîtes quantiques colloïdales (BQCs) et de leurs propriétés électriques et optiques uniques. Les BQCs sont des nanocristaux semi-conducteurs synthétisés en solution qui se comportent comme des atomes artificiels. Des progrès considérables ont été réalisés durant la dernière décennie pour développer une optoélectronique à base de films BQCs mais les performances des composants réalisés sont toujours limitées par un certain nombre de propriétés propres à ces milieux telles que leur granularité et la présence de ligands à la surface des nanocristaux. Un deuxième type de matériaux artificiels, les métamatériaux, suscite un intérêt considérable de la part de la communauté de la nano-optique en raison des perspectives qu'ils offrent pour surmonter la limite de diffraction, réaliser des capes d'invisibilités et des indices de réfraction négatif en optique. Cependant, un certain nombre des applications potentielles des métamatériaux optiques se heurtent à leurs pertes élevées et au manque de fonctionnalités actives contrôlées électriquement.Bien que les films BQCs et les métamatériaux soient étudiés de façon indépendante et associés à deux champs de recherche distincts, leurs propriétés ont beaucoup d'éléments en commun puisqu'elles sont dans les deux cas largement dictées par leur géométrie interne. Il paraît donc intéressant d'exploiter ces analogies et de voir si les difficultés rencontrées dans chaque discipline ne peuvent pas être surmontées en combinant les deux approches. Cette thèse se propose de jeter les premiers ponts entre films BQCs et métamatériaux et constitue une première tentative d'établir une synergie entre ces deux types de milieux artificiels.Dans un premier temps, nous étudions des réseaux de nanoantennes plasmoniques capables d'exalter la photoluminescence spontanée de BQCs et apportons de nouveaux éléments de compréhension à ces interactions. Ensuite, nous décrivons la fabrication et la caractérisation de LEDs à BQCs inorganiques et émission par le haut. Ces LEDs sont développées de façon à servir de plateforme pour la dernière partie de ce travail qui consiste à hybrider les films BQCs et les métamatériaux. Dans cette dernière partie, nous insérons les réseaux d'antennes plasmoniques étudiés précédemment dans l'architecture des LEDs et démontrons une nouvelle forme d'électroluminescence artificielle. Celle-ci se traduit par l'émission de lumière par des nanopixels discrets qui peuvent être arrangés de façon arbitrairement complexe afin de générer toute une gamme de fonctionnalités. D'autres avantages seront présentés comme une brillance accrue, une tension de seuil extrêmement basse, des longueurs d'ondes d'émission contrôlées par la géométrie et un contrôle total de la polarisation. Une série d'expériences visant à sonder les mécanismes à l’œuvre dans ce nouveau type de LEDs sera présentée.Ce travail illustre le très grand potentiel qu'il y a à combiner différentes classes de matière artificielle et suggère que bien d'autres opportunités découleront d'une vision unifiée des différents milieux composites développés en physique, chimie et ingénierieA next generation of electronic and optoelectronic devices with high performances and low cost is expected to take off with films of colloidal quantum dots (CQDs) thanks to their unique electrical and optical properties. CQDs are semiconducting nanocrystals synthesized in solution that behave as artificial atoms. Substantial progresses in CQD film-based optoelectronics has been made over the past decade, but the performances are still limited and governed by the merit and inherited properties of CQDs. Another type of artificial medium, metamaterials, is generating a considerable interest from the nano-optics community because of its promises for beating the diffraction limit, realizing invisible cloaks, and creating negative refractive of index at optical regime. However, many of the potential applications for optical metamaterials are limited by their losses and the lack of active functionalities driven by electricity.Although films of CQDs and metamaterials are studied independently and associated to two distinct fields, their properties are mainly determined by their inner geometry. In addition, the difficult hurdles from each field can be surmounted by cooperating with the other one. This dissertation establishes the first bridge to connect films of CQDs and metamaterials and is a first attempt at exploiting the synergy of different types of artificial media.Firstly, we study plasmonic nanoantenna arrays capable of enhancing the spontaneous photoluminescence of CQDs and provide new fundamental insight into these interactions. Secondly, we report the fabrication and characterization of the first inorganic top-emission infrared quantum dot light-emitting-diodes (QDLEDs). The diodes are developed to serve as a solid platform for studying the CQDs film/metamaterial hybrids. Finally, we insert the plasmonic nanoantenna arrays studied at the beginning of this thesis in our QDLEDs and demonstrate a novel form of electroluminescence in which light is emitted by discrete nanoscale pixels that than be arranged at will to form complex light emitting metasurfaces. Other advantages associated with our metamaterial QDLEDs will also be presented i.e. greatly enhanced brightness, extremely low turn-on voltage, emissive color tunability, and polarized electroluminescence. A series of controlled experiments to probe the operational mechanisms of metamaterial QDLED will be discussed.This demonstration illustrates the enormous synergy of combining different types of artificial matter and suggests that many other opportunities will arise by taking an unified view of the various artificial media developed in physics, chemistry and engineering
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McMahan, Michael T. « Metamaterial absorbers for microwave detection ». Thesis, Monterey, California : Naval Postgraduate School, 2015. http://hdl.handle.net/10945/45904.
Texte intégralRésumé :
Approved for public release; distribution is unlimitedThe development of high-power microwave weapons and dependence on electronics in modern weapon systems presents a high-power microwave weapons threat in future military conflicts. This study experimentally determines the absorption characteristics of simple metamaterial devices to potentially be used as protection and identification mechanisms, constructed through standard printed circuit board manufacturing processes, in the microwave region. Experimental results and analysis techniques are presented confirming absorption peaks in the anticipated microwave frequency range. The experimental results are compared to a finite-element model of these metamaterials confirming the ability to accurately model and predict absorption characteristics of similar metamaterial structures. Utilization of the absorption characteristics of these types of metamaterial structures to develop a microwave detector and/or equipment shielding is discussed. Several applications for such type of a detector are presented.
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Wang, Weijen 1980. « Directive antenna using metamaterial substrates ». Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17995.
Texte intégralRésumé :
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 83-86).
Using a commercially available software(CST Microwave Studio®), two kinds of simulations have been carried out on different metamaterials in the microwave regime. One is transmission and reflection of a unit cell in a waveguide, and the other is parallel plate slab farfield radiation. The S-parameters are obtained from the wave-guide simulation and are used to retrieve the effective permittivity and permeability with which we can estimate the farfield radiation using analytic method. Thus, by comparing the farfield radiation from two different methods, analytic and slab simulation, we find that the analytic method is able to indicate many major features of the slab simulation's farfield results, implying that within a certain frequency range, we can treat the metamaterial as being homogeneous. After comparing the radiation performance of different metamaterial as antenna substrates, a structure is chosen to be optimized in such a way that it improves in radiation power, beamwidth, and bandwidth.
by Weijen Wang.
M.Eng.
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Hasan, Md Kamrul. « Metamaterial Antenna for Medical Applications ». University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367944880.
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Erentok, Aycan. « Metamaterial-Based Electrically Small Antennas ». Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195725.
Texte intégralRésumé :
The introduction of the so-called metamaterials, artificial materials which have engineered electromagnetic responses that are not readily available in nature, and their exotic properties have provided an alternate design approach that has led to improved performance characteristics of several radiating and scattering systems. This dissertation work introduces an antenna design paradigm based on the incorporation of metamaterials, which have negative permittivity and/or permeability medium properties, with simple radiating elements to obtain efficient electrically-small antenna systems. The most general analytical form of the electrically-small electric dipole antenna in the presence of a multilayered metamaterial shell system is developed and the total radiated power of this system is optimized using a hybrid genetic algorithm(GA)-MATLAB optimization approach. The numerical modeling of more realistic antenna-metamaterial systems confirms the analytical results. The theoretical and numerical studies of their radiation and resonance behaviors have led this dissertation work to the discovery of the first physical two- (2D) and three-dimensional (3D) metamaterial based and inspired efficient electrically-small antenna systems. Several novel metamaterial-inspired electrically-small antenna systems, i.e., the 2D and 3D electrical- and magnetic-based EZ antennas, are reported and are shown to be naturally matched to a 50 Ohms source and, hence, to have high overall efficiencies. The proposed 2D and 3D EZ antenna systems are linearly scalable to a wide range of frequencies. Several versions of the 2D EZ antennas were fabricated and tested. The measurement results confirm the performance predictions. This dissertation also considers several new metamaterial structures. An artificial magnetic conductor (AMC) slab is designed to achieve its in-phase reflection properties in the X-band at 10 GHz without the presence of a PEC ground plane. A block of this AMC structure was designed, fabricated, tested, and then integrated with a dipole antenna to realize a resonant low profile antenna system having a large front-to-back ratio.
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Thomas, John Rhodes. « Investigation of properties of materials with negative permittivity and permeability : negative refraction / ». Thesis, Connect to this title online ; UW restricted, 2006. http://hdl.handle.net/1773/6113.
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Ambrosio, Leonardo Andre 1980. « Feixes localizados em pinças opticas com particulas convencionasi e metamateriais ». [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260409.
Texte intégralRésumé :
Orientador: Hugo Enrique Hernandez Figueroa, Michel zamboni RachedTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
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Resumo: Nesta tese, abordamos aplicações de feixes localizados em FSO - Free Space Optics - e em pinças ópticas, com ênfase maior para o segundo. No primeiro caso, mostramos que é possível pré-determinar o padrão de intensidade longitudinal através de elementos ópticos adequadamente modelados em suas funções de fase: os áxicons. Assim, estes feixes poderiam ser usados para alinhar o link. No caso de pinças ópticas, exploramos a idéia de que, em breve, será possível a contrução de partículas esféricas homogêneas, na escala micrométrica, com índice de refração negativo (as chamadas DNG particles, ou Double-Negative particles), e verificamos as propriedades de aprisionamento óptico tanto para feixes gaussianos quanto para feixes localizados, no regime de óptica geométrica e no caso mais geral da teoria eletromagnética. A idéia de que partículas são atraídas para regiões de alta intensidade quando seu índice de refração é maior do que o do meio, e para regiões de baixa intensidade quando este índice é menor, embora válida para partículas convencionais - aquelas com índice de refração positivo -, deve ser revista para partículas DNG.
Abstract: In this thesis, we explore some applications of localized beams in FSO - Free Space Optics - and optical tweezers, greater emphasis been given to the second one. For FSO, we show that it is possible to choose the desired longitudinal intensity pattern by using optical elements adequately modeled in their phase functions: the axicons. In this way, these beams could be uses for optical alignment of the link. In the case of optical tweezers, we investigate the possibility that it will soon be possible to design and build homogeneous spherical particles, in the micron scale, with negative refractive index (the so called DNG particles, or Double-Negative particles), and we verify some properties related to optical trapping, both for Gaussian and Bessel beams, in the optics ray regime and in the more general electromagnetic case. The idea that particles with refractive index higher than the medium in which it is immersed is attracted to regions of high intensity, whereas it is attracted to regions of low intensity when its refractive index is lower than the medium, although valid for conventional particles - those with positive refractive index - must be revisited for DNG particles.
Doutorado
Telecomunicações e Telemática
Mestre em Engenharia Elétrica
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Shelton, David. « TUNABLE INFRARED METAMATERIALS ». Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3925.
Texte intégralRésumé :
Metamaterials are engineered periodic composites that have unique refractive-index characteristics not available in natural materials. They have been demonstrated over a large portion of the electromagnetic spectrum, from visible to radiofrequency. For applications in the infrared, the structure of metamaterials is generally defined using electron-beam lithography. At these frequencies, the loss and dispersion of any metal included in the composite are of particular significance. In this regard, we investigate deviations from the Drude model due to the anomalous skin effect. For comparison with theoretical predictions, the optical properties of several different metals are measured, both at room temperature and at 4 K. We extend this analysis to the coupling between plasmon and phonon modes in a metamaterial, demonstrating that very thin oxide layers residing at the metal-substrate interface will significantly affect the spectral location of the overall resonance. Oxide-thickness-dependent trends are then explored in some detail. Potential applications of this general area of study include surface-enhanced infrared spectroscopy for chemical sensing, and development of narrowband notch filters in the very long wavelength infrared. We then consider various possibilities for development of tunable infrared metamaterials. These would have wide applicability in dynamically variable reflectance surfaces and in beam steering. We consider several methods that have been previously shown to produce tunable metamaterials in the radio frequency band, and explore the challenges that occur when such techniques are attempted at infrared frequencies. A significant advance in tunable-infrared-metamaterial technology is then demonstrated with the use of thermochromic vanadium dioxide thin films. Highlights include the first demonstration of a tunable reflectarray in the infrared for active modulation of reflected phase, the first demonstration of a tunable resonance frequency in the thermal infrared band, and the largest resonance-frequency shift recorded to date in any part of the infrared. Finally, future work is proposed that holds the promise of wideband frequency tuning and electronically-controllable metamaterials.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr PhD
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Yang, Biao. « Photonic topological metamaterials ». Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8103/.
Texte intégralRésumé :
Topology, a mathematical concept associated with global perspectives, was found to represent geometric aspects of physics. To date, various topological phases have been proposed and classified. Among them, topological gapless phases focusing on the degeneracies of energy bands serving as the singularities in the momentum space, attract much attention. Especially in the three-dimension, various topological semimetals have been proposed. With unit topological charge ±1, Weyl degeneracies have laid the foundation. Also, they show loads of exotic properties, such as Fermi arcs and chiral anomalies. Being relied on the band topology theory, topological gapless phases have also been transferred into classic systems, such as photonics, acoustics and mechanics. Here, we experimentally investigated photonic Weyl systems in the photonic continuum media, where electromagnetic intrinsic degrees of freedom play key roles in constructing the state space. Firstly, we researched chiral hyperbolic metamaterials, a type-II Weyl metamaterials, from which we directly observed topological surface-state arcs. Then, we report the discovery of ideal photonic Weyl systems, where helicoid structure of nontrivial surface states has been demonstrated. Finally, we construct photonic Dirac points, through analysing eigen reflection field, we found the correlation of topological charges in momentum and real spaces.
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Atmatzakis, Evangelos. « Bimetallic photonic metamaterials ». Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/399982/.
Texte intégralRésumé :
In this thesis, I introduce bimetallic ring resonator arrays as a platform for enhancing and controlling magneto-optical and thermoelectric effects. By taking advantage of differences in the physical (optical, electronic, thermal, magnetic) properties of the two elements comprising the resonators, I have demonstrated tailoring of the optical absorption and the Faraday effect, and generation of THz magnetic pulses. In particular: I have theoretically predicted for the first time the light-driven generation of intense, highly-localised, THz magnetic pulses in thermoelectric metamaterials. Excitation of bimetallic plasmonic resonators by ultrafast electromagnetic pulses, raises the electron energy and causes them to diffuse towards colder regions due to the thermoelectric effect. In addition, the resonator design and the excitation polarization create a situation in which electrons are forced to migrate in the azimuthal direction along the circumference of the ring, giving rise to a quasistatic magnetic field of up to 0:35 T, localized in an area with diameter of 70 nm. The time dynamics of the pulse generation process are controlled by electron energy relaxation to lattice through electron-phonon collisions, which lead to pulse duration of ~ 1:8 ps. I have demonstrated experimentally for the first time enhanced Faraday rotation in bimetallic single-layer metamaterials. The design of the unit cell resonator allows light confinement in the vicinity of the magneto optically active ferromagnetic metal which results in enhancement of the Faraday effect. Tailoring the size of the ferromagnetic component, which simultaneously controls the magneto-optical response and the dissipation losses in the system, results in a design which rotates the polarization azimuth of an incident electromagnetic wave by up to 1 mrad. I have demonstrated for the first time resonant absorption in single-layer Au/Ni photonic metamaterials and investigated its dependence on wavelength and polarization. A hybrid system consisting of materials that exhibit different levels of dissipation losses can be excited in ways which enable control over the spectral position, bandwidth and level of the optical absorption. The plasmonic modes mediating the metamaterial absorption are identified by a detailed computational analysis, which is in good agreement with the far-field experimental observations. I have fabricated for the first time single-layer, bimetallic ring resonator arrays consisting of noble and ferromagnetic metals. An optimized, multi-step electron beam lithography process has been developed in order to bring together, with sub-10 nm accuracy, the two metallic sectors and form 100 x 100 µm2 ring resonator arrays. I have developed a sensitive polarimeter apparatus to probe polarization rotation in metamaterial arrays. Following the principles of polarization modulation polarimetry, I have built a state of the art experimental setup that resolves angles as low as 10-5 radians in finite size, strongly scattering samples which have dimensions down to 50 x 50 µm2.
21
Plum, Eric. « Chirality and metamaterials ». Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/301296/.
Texte intégralRésumé :
Electromagnetic metamaterials are artificial media that derive novel properties from periodic structuring on the sub-wavelength scale. Here, the consequences of two-dimensional (2D) and three-dimensional (3D) chirality for the electromagnetic properties of metamaterials are investigated. The focus of this work is on new ways of achieving circular conversion dichroism, optical activity and negative refraction in highly symmetric structures. In the theoretical part of this work, fundamental constraints on polarization effects in planar metamaterials are established based on symmetry and energy conservation considerations. Through the experimental study of 2D chirality, I have first observed circular conversion dichroism (i) in non-chiral structures and (ii) due to 2D-chiral arrangement of non-chiral elements. (iii) I have first seen enantiomerically sensitive reflection, yielding the experimental demonstration that circular conversion dichroism results in simultaneous directional asymmetries in transmission, reflection and absorption. In particular, a tunable transmission asymmetry of up to 21 % has been observed when extrinsic 2D chirality was associated with oblique incidence onto a non-chiral meandering wire pattern. At normal incidence circular conversion dichroism was seen for non-chiral split ring elements assembled into a 2D-chiral double-periodic array. Simultaneous directional and enantiomeric asymmetries in transmission (16 %), reflection (16 %) and absorption (32 %) were observed for normal incidence onto a double-periodic array of 2D-chiral split rings. Regarding 3D chirality, I have (i) realized the first material with a negative refractive index due to chirality and (ii) observed optical activity in the first stereometamaterial. (iii) I have discovered that optical activity can be observed in non-chiral metamaterials and (iv) I have demonstrated that optical activity in such structures is tunable and occurs in transmission and reflection. In particular polarization rotation reaching 81± and circular dichroism of up to 26 dB have been observed for non-chiral arrays of split rings, when an extrinsically 3D-chiral experimental arrangement was formed by metamaterial and direction of incidence. Based on a previously-studied meta-molecule consisting of mutually twisted metal patterns in parallel planes, microwave and photonic stereometamaterials with optical activity have been realized in this thesis and such a structure has been shown to have a negative refractive index of -1.7 for right-handed circularly polarized microwaves.
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Ou, J. Y. « Reconfigurable photonic metamaterials ». Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/379328/.
Texte intégralRésumé :
This thesis reports on the development of a new class of switchable nanostructured photonic metamaterials, Reconfigurable Photonic Metamaterials (RPMs). Over the last decade, fascinating material properties including negative refraction, optical magnetism, invisibility, asymmetric transmission, perfect lenses and many more were demonstrated in metamaterials. Inspired by pioneering work on micro-electro mechanical metamaterials for the terahertz and microwave spectral regions with feature sizes from millimeters to tens and hundreds microns, I develop reconfigurable photonic metamaterials for the optical spectral range that have sub-micron meta molecules and nanoscale design features. In particular, for the first time I developed: Novel fabrication processes for manufacturing reconfigurable photonic metamaterials based on the platform of elastic silicon nitride membranes using focused ion beam lithography, film deposition, precise alignment, etching and annealing techniques. These fabrication techniques have allowed the manufacturing of a wide range of reconfigurable metamaterials consisting of bi-layer (gold/silicon nitride) or tri-layer (gold/silicon nitride/gold) structured membranes suitable for applications as plasmonic RPMs. Novel RPMs tunable by ambient temperature that operate in the optical and near infrared parts of the spectrum. With such metamaterials exploiting the change in plasmonic response due to differential thermal expansion in bimorph nanostructures I have demonstrated 50% changes in optical transmission at the wavelength of 1735 nm when the temperature is ramped from 76 K to 270 K. Novel RPMs operating in the near-infrared part of the spectrum that can be controlled by electric signals. These types of metamaterials harness electrostatic forces on the nanoscale and offer up to 20 MHz modulation bandwidth. At a threshold level of stimulation these metamaterials exhibit non-volatile switching with up to 250% transmission change. As a part of this research I developed a characterization technique that allows imaging and recording of the electrostatic switching under a scanning electron microscope. Novel optically controlled RPMs exploiting near-field optical forces induced by light and optical heating for reconfiguration. Such metamaterials show a new type of optomechanical nonlinearity leading to intensity-dependent transmission that exceeds the cubic nonlinearity of GaAs by seven orders of magnitude. Using CW diode lasers operating at telecommunication wavelengths of 1.3 μm and 1.55 μm I have demonstrated cross-wavelength optical modulation with amplitude of about 1 % that can be achieved at only about 1 mW of average power of the control beam. I also developed the numerical analysis of thermo-opto-mechanical properties of the structures and calculated eigenmodes and cooling constants of the RPMs under modulated laser irradiation. Overall, the development of reconfigurable photonic metamaterials provides a new and flexible platform for the control of metamaterial properties "on demand". Such metamaterials can find applications in sensors, tunable spectral filters, switches, modulators, programmable transformation optics devices and any other application where tunable optical properties are required.
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Jenett, Benjamin(Benjamin Eric). « Discrete mechanical metamaterials ». Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/130610.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, September, 2020Cataloged from the official PDF version of thesis.
Includes bibliographical references (pages 127-136).
Digital fabrication enables complex designs to be realized with improved speed, precision, and cost compared to manual techniques. Additive manufacturing, for example, is one of the leading methods for rapid prototyping and near net shape part production. Extension to full scale structures and systems, however, remains a challenge, as cost, speed and performance present orthogonal objectives that are inherently coupled to limited material options, stochastic process errors, and machine-based constraints. To address these issues, this thesis introduces new materials that physically embody attributes of digital systems, scalable methods for automating their assembly, and a portfolio of use cases with novel, full-scale structural and robotic platforms. First, I build on the topic of discrete materials, which showed a finite set of modular parts can be incrementally and reversibly assembled into larger functional structures.
I introduce a new range of attainable properties, such as rigidity, compliance, chirality, and auxetic behavior, all within a consistent manufacturing and assembly framework. These discretely assembled mechanical metamaterials show global continuum properties based on local cellular architectures, resulting in a system with scalability, versatility, and reliability similar to digital communication and computation. Next, I present a new kind of material-robot system to enable methods of assembly automation. Rather than relying on global motion control systems for precision, mobile robots are designed to operate relative to their discrete material environment. By leveraging the embedded metrology of discrete materials, these relative robots have reduced complexity without sacrificing extensibility, enabling the robots to build structures larger and more precise than themselves.
Multi-robot assembly is compared to stationary platforms to show system benefits for cost and throughput at larger scales. Finally, I show a range of discretely assembled systems that blur the boundary between structure and robotics. Full-scale demonstrations include statically reconfigurable bridges, supermileage racecars, and morphing aero and hydrodynamic vehicles. Performance scaling is projected to new regimes, using case studies of turbine blades, airships, and space structures. These discrete systems demonstrate new, disruptive capabilities not possible within the limits of traditional manufacturing.
by Benjamin Eric Jenett.
Ph. D.
Ph.D. Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences
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Ferrer, González Pere Josep. « Multifunctional metamaterial designs for antenna applications ». Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/312841.
Texte intégralRésumé :
Over the last decades, Metamaterials (MTMs) have caught the attention of the scientific community. Metamaterials are basically artificially engineered materials which can provide unusual electromagnetic properties not present in nature. Among other novel and special EM applications, such as the negative refraction index (NRI) application, Metamaterials allow the realisation of perfect magnetic conductors (PMCs), which are of interest in the development of smaller and more compact antenna systems composed of one or more antennas.
In this context, this thesis is focused on investigating the feasibility of using metamaterial structures to improve the performance of antennas operating at the microwave frequencies. The metamaterial design process is challenging because metamaterials are primarily composed of resonant particles, and hence, their response is frequency dependent due to the dispersive behaviour of their effective medium properties. However, one can take advantage of this situation by exploiting those strange properties while finding other antenna applications for such metamaterial designs. For the case of the PMC applications, the relative magnetic permeability values are negative, because they are found just above the resonance of the metamaterial.
This thesis investigates several antenna applications of artificial magnetic materials (AMMs). The initial work is devoted to the design of a spiral resonator (SR) AMM slab to realise a low profile reflector dipole antenna by taking advantage of its PMC response. The spiral resonator has been used due to its reduced unit cell size when compared to other metamaterial resonators, leading to a more homogeneous metamaterial structure. In addition, a bidirectional PMC spacer has been applied to produce a small and compact antenna system composed of two monopole antennas, although the concept may be applied to other antenna types. A third application as an AMC reflector are the transpolarising surfaces, where the incident electric field plane wave is reflected at a polarisation rotation angle of 90 degrees. Such surfaces may be of interest to produce high cross-polar response reflecting devices, like the modified trihedral corner reflector that has been tested for polarimetric synthetic aperture radar (PolSAR) purposes.
Another application of the SR AMM metamaterial is the patch antenna with a magneto-dielectric loading. The relative magnetic permeability of the AMM metamaterial has values over the unity in the frequency band below the resonance. As a consequence, the patch antenna can be miniaturised without reducing its bandwidth of operation, in contrast to a typical high dielectric permittivity substrate.
Finally, the SR AMM metamaterial also presents values of relative magnetic permeability between zero and the unity (MNZ). In such a case, the SR AMM metamaterial has been applied as an MNZ cover of a slot antenna, devoted to increasing the broadside radiated power and directivity of the antenna.En las últimas décadas, los Metamateriales (MTMs) han captado la atención de la comunidad científica internacional. Los metamateriales son básicamente materiales artificiales diseñados que tienen propiedades electromagnéticas inusuales no presentes en la naturaleza. Aparte de otras aplicaciones innovadoras en electromagnetismo, como la posibilidad de un material con un índice de refracción negativo (NRI), los metamateriales permiten realizar los conductores magnéticos perfectos (PMCs), que podrían ser de gran utilidad para implementar sistemas de múltiples antenas más pequeños y compactos. En este contexto, esta tesis se centra en investigar el uso de diferentes diseños de metamateriales para mejorar las prestaciones de sistemas radiantes o antenas que trabajan a frecuencias de microondas. El proceso de diseño de los metamateriales es complicado, porque los metamateriales están compuestos de resonadores magnéticos, y consecuentemente, su respuesta varía con la frecuencia a causa de la naturaleza dispersiva de sus parámetros de medio efectivo. No obstante, se pueden aprovechar estas propiedades extrañas para encontrar otras aplicaciones interesantes en antenas. Para el caso de aplicaciones como PMC, el valor de la permeabilidad magnética relativa toma principalmente valores negativos, ya que se encuentran después de la resonancia del metamaterial. Esta tesis realiza el estudio de diferentes aplicaciones de antenas con materiales magnéticos artificiales (AMMs). Primeramente, se ha diseñado un metamaterial AMM compuesto de resonadores en espiral (SRs), que se aplica para realizar un reflector de perfil bajo con una antena dipolo, aprovechando la respuesta PMC que proporciona el metamaterial. Se han utilizado resonadores en forma de espiral porque tienen una celda unidad más reducida al compararla con la de otros resonadores metamaterials, produciendo así una estructura metamaterial más homogénea. Además, un diseño PMC bidireccional ha permitido diseñar un sistema pequeño y compacto de dos antenas monopolo, aunque este concepto se puede aplicar a otros tipos de antenas. Una tercera aplicación como reflector AMC es el de pantalla transpolarizadora, dónde una onda eléctrica plana incidente es reflejada con un ángulo de rotación de 90 grados. Estas pantallas pueden servir para realizar dispositivos reflectores con una respuesta cruzada alta, como pasa con un triedro modificado que se ha probado con éxito en aplicaciones como calibrador de radar de apertura sintética polarimétrico (PolSAR). El metamaterial SR AMM también se ha utilizado como substrato magneto-dieléctrico de una antena impresa o patch. La permeabilidad magnética relativa de este metamaterial toma valores más grandes que la unidad en el rango de frecuencias por debajo de la resonancia. Por esto, la antena patch se puede miniaturizar sin reducir sus prestaciones de ancho de banda de operación, caso contrario a cuando se utilizan substratos de permitividad dieléctrica alta. Finalmente, el metamaterial SR AMM también toma valores de permeabilidad magnética relativa entre cero y la unidad (MNZ). En este caso, el metamaterial SR AMM se ha aplicado como un superestrato MNZ de una antena de ranura o slot, con la intención de incrementar la potencia radiada y la directividad de la antena.
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Hedayati, Mehdi Keshavarz [Verfasser]. « Tunable Plasmonic Metamaterial / Mehdi Keshavarz Hedayati ». Kiel : Universitätsbibliothek Kiel, 2014. http://d-nb.info/1055941444/34.
Texte intégral
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Peruch, Silvia. « Ultrafast properties of plasmonic nanorod metamaterial ». Thesis, King's College London (University of London), 2016. https://kclpure.kcl.ac.uk/portal/en/theses/ultrafast-properties-of-plasmonic-nanorod-metamaterial(d981b5e4-b959-4193-8cf1-219b68de08d6).html.
Texte intégralRésumé :
Plasmonic metamaterials have customized linear and nonlinear optical properties. This thesis investigates the properties of an anisotropic plasmonic metamaterial, consisting of aligned, interacting gold nanorods, to perform ultrafast light modulation, exploiting the intrinsic Kerr nonlinearity of gold. This e ect is based on an illumination-intensity-dependent change in the gold's permittivity, which takes place on ultrafast timescales and induces the intensity-dependent change of the metamaterial's re ection and transmission. A comprehensive theoretical and numerical analysis of the linear and nonlinear response of various con gurations of the metamaterial is performed and compared to experimental results. A new family of hyperbolic waveguided modes above the e ective plasma frequency, enabled by spatial dispersion, is identi ed. The strong nonlinear response and the dynamic modulation capabilities associated with the excitation of the waveguided modes is investigated. The presence of strong electron temperature gradients in the nanorods induced by a control light is shown to determine a stronger nonlinear modulation and to in uence the dynamic response, leading to subpicosecond time recovery components of the nonlinearity. Weak and strong coupling between molecular excitons and the metamaterial's modes can be achieved using core-shell nanorod geometries. The coherent interaction of molecular J-aggregates with coreshell nanorod arrays is analyzed in both the weak and strong coupling regimes. Subpicosecond components of the modulation are determined in the strong coupling conditions. The design of the optical response of the gold nanorod and core-shell metamaterials is studied through the near- to mid- Infrared, key spectral regions for molecular ngerprinting in chemical sensing and absorption spectroscopy. The applicability limits of the analytic approaches using the quasi-static and e ective medium approximations is tested. The results show great potential of the plasmonic nanorod metamaterial for ultrafast nonlinear optics in free-space and integrated applications, in a broad spectral range.
27
Phillips, Allan T. « Resonant terahertz absorption using metamaterial structures ». Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/27888.
Texte intégralRésumé :
The Sensor Research Lab at the Naval Postgraduate School is developing a real-time THz imaging camera. Vital to its design is the metamaterial absorbing layer (metafilm) within each pixel that allows for THz absorption. While there are numerous applications in the THz region, sensors and sources for THz energy have much room for improvement. The use of metamaterial technology for the purpose of a THz sensor has the potential to reduce costs while greatly improving sensitivity performance. The Sensor Research Lab has fabricated metafilms capable of near 100 percent absorption. In this research project, absorption characteristics of a set of metamaterials were measured using Fourier transform THz spectroscopy and modeled using an RLC circuit. The model provides a good description of the absorption characteristics and should assist in better understanding of the electromagnetic interactions within the metafilm.
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Liu, Xianliang. « Infrared Metamaterial Absorbers : Fundamentals and Applications ». Thesis, Boston College, 2013. http://hdl.handle.net/2345/3829.
Texte intégralRésumé :
Thesis advisor: Willie J. PadillaRealization of an ideal electromagnetic absorber has long been a goal of engineers and is highly desired for frequencies above the microwave regime. On the other hand, the desire to control the blackbody radiation has long been a research topic of interest for scientists--one particular theme being the construction of a selective emitter whose thermal radiation is much narrower than that of a blackbody at the same temperature. In this talk, I will present the computational and experimental work that was used to demonstrate infrared metamaterial absorbers and selective thermal emitters. Based on these work, we further demonstrate an electrically tunable infrared metamaterial absorber in the mid-infrared wavelength range. A voltage potential applied between the metallic portion of metamaterial array and the bottom ground plane layer permits adjustment of the distance between them thus altering the electromagnetic response from the array. Our device experimentally demonstrates absorption tunability of 46.2% at two operational wavelengths. Parts of this thesis are based on unpublished and published articles by me in collaboration with others. The dissertation author is the primary researcher and author in these publications. The text of chapter two, chapter five, and chapter seven is, in part, a reprint of manuscript being prepared for publication. The text of chapter three is, in part, a reprint of material as it appears in Physical review letters 104 (20), 207403. The text of chapter four is, in part, a reprint of material as it appears in Physical Review Letters 107 (4), 45901. The text of chapter six is, in part, a reprint of material as it appears in Applied Physics Letters 96, 011906
Thesis (PhD) — Boston College, 2013
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Brito, Davi Bibiano. « Metamaterial inspired improved antennas and circuits ». Universidade Federal do Rio Grande do Norte, 2010. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15152.
Texte intégralRésumé :
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Metamaterials exhibiting negative refraction have attracted a great amount of attention in recent years mostly due to their exquisite electromagnetic properties. These materials are artificial structures that exhibit characteristics not found in nature. It is possible to obtain a metamaterial by combining artificial structures periodically. We investigated the unique properties of Split Ring Resonators, High impedance Surfaces and Frequency Selective Surfaces and composite metamaterials. We have successfully demonstrated the practical use of these structures in antennas and circuits. We experimentally confirmed that composite metamaterial can improve the performance of the structures considered in this thesis, at the frequencies where electromagnetic band gap transmission takes place
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Aquino, Manoel do Bonfim Lins de. « Antena de microfita com substrato metamaterial ». Universidade Federal do Rio Grande do Norte, 2008. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15224.
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This paper presents a theoretical and numerical analysis of the parameters of a rectangular microstrip antenna with metamaterial substrate. The metamaterial (MTM) theory was applied along with Transverse Transmission Line (LTT) method to characterize substrate quantities and obtain the general equations of the electromagnetic fields. A study on metamaterial theory was conducted to obtain the constructive parameters, which were characterized through permittivity and permeability tensors to arrive at a set of electromagnetic equations. Electromagnetic principes are used to obtained parameters such as complex resonance frequency, bandwidth and radiation pattern were then obtained. Different metamaterial and antenna configurations were simulated to miniaturize them physically and increase their bandwidth, the results of which are shown through graphics. The theoretical computational analysis of this work proved to be accurate when compared to other studies, and may be used for other metamaterial devices. Conclusions and suggestions for future work are also proposed
Este trabalho apresenta a an?lise te?rica e num?rica dos par?metros de uma antena de microfita tipo patch retangular sobre substrato metamaterial. Para isso, ? aplicada a teoria de metamateriais - MTM, em conjunto com o m?todo da Linha de Transmiss?o Transversa - LTT, para a caracteriza??o das grandezas do substrato e obten??o das equa??es gerais dos campos eletromagn?ticos. ? realizado um estudo acerca da teoria de metamateriais com o intuito de obter seus par?metros construtivos, os mesmos s?o caracterizados atrav?s de tensores permissividade e permeabilidade. Essa teoria ? aplicada ao m?todo da Linha de Transmiss?o Transversa chegando-se ?s equa??es gerais para os campos eletromagn?ticos da antena. Em seguida s?o utilizados princ?pios da teoria eletromagn?tica para obter-se caracter?sticas como: freq??ncia de resson?ncia complexa, diagramas de radia??o e largura de banda. S?o simulados diferentes configura??es de metamateriais e antenas com o intuito de miniaturizar as dimens?es f?sicas e aumentar a largura de banda das mesmas, os resultados s?o apresentados atrav?s de gr?ficos. A an?lise te?rica computacional deste trabalho se mostra precisa, em compara??o a outros, podendo ser empregado em dispositivos que utilizem metamateriais como substratos. Ao final s?o apresentadas conclus?es e sugest?es para trabalhos futuros
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Lei, Qin. « All dielectric composites for metamaterial applications ». Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:2dd643a5-7590-44a2-833a-148ffaa655f6.
Texte intégralRésumé :
This thesis describes my work on manufacturing of all dielectric polymer/ceramic composites for electromagnetic property customisation at microwave frequencies. Electromagnetic wave manipulation can be achieved with the help of transformation optics concept and metamaterials with desired permittivity and permeability properties. The use of all-dielectric metamaterials, in particular, offers a novel solution to broadband, low loss microwave devices. In this work, polymer/ceramic composites were studied to provide materials with a wide range of permittivity that can be customised precisely by optimised manufacturing routes. Thermoplastic perfluoroalkoxy (PFA) and thermoset epoxy were mainly used as polymer matrices and ferroelectric powders such as barium titanate used as ceramic fillers. Different composite types were fabricated by spraying, casting and 3D printing, with each manufacturing method carefully studied to produce stable and uniform composite quality. The microstrcutures of these composites were examined by microtomy and SEM and the dielectric properties were assessed by impedance and waveguide measurements for difference microwave frequency ranges. Controllable dielectric constants from 3 to 18 with high accuracy in epoxy/BT composites were achieved at 12 - 18 GHz. These composites were then used to fabricate advanced microwave devices such as the power divider lens to demonstrate my capability of permittivity customisation. Simulations for these advanced applications were done in Comsol Multiphysics and were compared to the experimental results.
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Maassel, Michael. « A Metamaterial-Based Multiband Phase Shifter ». Diss., North Dakota State University, 2014. https://hdl.handle.net/10365/27095.
Texte intégralRésumé :
A design methodology for a multi-band phase shifter using a metamaterial-based transmission line was developed. This method is different in that the loaded-line phase shifter has a phase shift of 90 degrees at the center frequencies of both bands instead of -90 degrees and -270 degrees. The method was validated using simulation and measured results.
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Ijaz, Bilal. « Metamaterial-Inspired Reconfigurable Series-Fed Arrays ». Diss., North Dakota State University, 2014. https://hdl.handle.net/10365/27593.
Texte intégralRésumé :
One of the biggest challenges in modern day wireless communication systems is to attain agility and provide more degrees of freedom in parameters such as frequency, radiation pattern and polarization. Existing phased array antenna technology has limitations in frequency bandwidth and scan angle. So it is important to design frequency reconfigurable antenna arrays which can provide two different frequency bandwidths with a broadside radiation pattern having a lower sidelobe and reduced frequency scanning. The reconfigurable antenna array inspired by the properties of metamaterials presented here provides a solution to attain frequency agility in a wireless communication system. The adaptive change in operating frequency is attained by using RF p-i-n diodes on the antenna array. The artificially made materials having properties of negative permeability and negative permittivity have antiparallel group and phase velocities, and, in consequence of that, they support backward wave propagation. The key idea of this work is to demonstrate that the properties of metamaterial non-radiating phase shifting transmission lines can be utilized to design a series-fed antenna array to operate at two different frequency bands with a broadside radiation pattern in both configurations. In this research, first, a design of a series-fed microstrip array with composite right/left-handed transmission lines (CRLH-TLs) is proposed. To ensure that each element in the array is driven with the same voltage phase, dual-band CRLH-TLs are adopted instead of meander-line microstrip lines to provide a compact interconnect with a zero phase-constant at the frequency of operation. Next, the work is extended to design a reconfigurable series-fed antenna array with reconfigurable metamaterial interconnects, and the expressions for array factor are derived for both switching bands.
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Venkatakrishnan, Rajiv Krishnan. « Compact Metamaterial UHF RFID Tag Antennas ». University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313767918.
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Noor, Adnan. « Metamaterial electromagnetic absorbers and plasmonic structures ». Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/metamaterial-electromagnetic-absorbers-and-plasmonic-structures(7028ac57-86c2-4557-8f57-1acb03ee8800).html.
Texte intégralRésumé :
In this thesis metamaterial radar absorbers and plasmonic structures have been investigated. Following a brief overview covering metamaterial structures, and their applications in various areas of Microwave Engineering, a novel thin metamaterial wideband radar absorber, formed by two layers of resistive Hilbert curve arrays, is proposed and analysed numerically in HFSS, revealing a reduction in Monostatic Radar Cross Section (RCS) of more than 10 dB from 9.1 to 18.8 GHz (70% fractional bandwidth) for both polarizations. The structure has thickness of only 0.11λ to 0.24λ at lowest and highest frequencies respectively. The lateral dimensions are only 0.13λ to 0.3λ per unit cell at lowest and highest frequencies respectively which is several times smaller than that of recently reported circuit analogue absorbers operating in the similar frequency band. Furthermore, a wideband terahertz Hilbert curve array is proposed and analyzed both theoretically and numerically, showing an absorption bandwidth of more than one octave. This was followed by study of plasmonic cloak for subwavelength conducting objects. It was demonstrated that a plasmonic cloak designed for a conducting sphere will work for non spherical conducting objects of similar dimensions as well. Finally spoof plasmonic structures were investigated. A novel plasmonic structure based on a modified Apollonian fractal array of cylindrical coaxial apertures in an aluminium sheet was proposed and analyzed. The structure exhibits negative group velocity with less than 3.5 dB attenuation. Plasmonic structure based on Sierpinski array of apertures was also investigated and found to give quite good extraordinary transmission bandwidth.
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Hao, Jianping. « Broad band electromagnetic perfect metamaterial absorbers ». Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10076/document.
Texte intégralRésumé :
Ce travail de thèse concerne les structures artificielles à base de métamatériaux permettant la réalisation d’absorbants parfaits. Après une brève introduction des métamatériaux, de leur fonctionnement en tant qu’absorbants et de l’état de l’art, quatre types de structures fonctionnant en bandes centimétrique ou millimétrique ont été conçus puis fabriqués à savoir (i) des réseaux de cubes BaSrTiO3 (BST) basés sur les résonances de Mie, (ii) des réseaux désordonnés composés d’anneaux métalliques mettant en jeu des effets de résonance semblables aux systèmes plasmoniques (iii) des absorbants à quatre résonateurs élémentaires sur substrat flexible et (iv) des réseaux multicouches métal-diélectrique de forme pyramidale. Pour l’ensemble, des simulations numériques, corroborées par l’expérience en guide d’onde ou en espace libre, montrent l’existence d’un moment magnétique. Celui-ci est induit par une boucle des courants de déplacement et de conduction. Pour les structures périodiques, les conditions de grande largeur de bande d’absorption ont été établies sur la base du piégeage et de la dissipation de l’énergie incidente. Pour les réseaux désordonnés, il est montré le rôle capital des couplages entre résonateurs. Des structures périodiques à base de ferroélectrique de dimensions sous longueur d’onde ont été assemblées avec succès tandis que des absorbants flexibles ont été réalisés par technique d’impression jet d’encre montrant l’amélioration d’un facteur quatre de la bande d’absorption. Des améliorations comparables ont été obtenues à l’aide de réseaux d’anneaux, dont les positions dans le plan sont désordonnées, résultant de la distribution des fréquences de résonance par effet de couplage fort entre les résonateursIn this thesis broadband Metamaterial Perfect Absorbers (MPAs) have been investigated. Following a brief introduction of metamaterials, operating mechanisms and state of the art of MPA, four absorber types operating either at centimeter or millimeter wavelengths have been designed and fabricated namely :(i) Mie-resonance based BaSrTiO3 (BST) arrays operating at microwaves, (ii) plasmonic-type disordered ring-shaped MPA, (iii) four patches millimeter wave flexible absorbers (iv) Pyramidal metal/dielectric stacked resonator arrays. For all the structures, it was demonstrated, through numerical simulations, assessed by characterization in a waveguide configuration or in free space, that unit absorbance relies on magnetic resonances induced by a current loop combining displacement and conduction currents. For periodic arrays, the condition for a broad band operation was established via the optimization of dissipation and trapping of electromagnetic energy in the resonators. For disordered metamaterials, it was shown the major role played by the magnetic dipole-dipole interaction. From the technological side, Ferroelectrics cube arrays with subwavelength dimensions were assembled onto a metal plate while flexible multi-resonators periodic arrays were successfully fabricated by ink-jet printing showing a fourfold enhancement of the absorbance bandwidth thanks to the overlapping of resonance frequencies. Comparable improvement in the bandwidth was also pointed out with randomly position metal ring arrays due to the distribution of resonance frequencies that result from tight in-plane resonator coupling
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Heffernan, Travis Jade. « Metamaterial Enhanced Wireless Power Transmission System ». DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1069.
Texte intégralRésumé :
Nikolai Tesla's revolutionary experiments demonstrated the possible benefits of transmitting power wirelessly as early as 1891. Applications for the military, consumers, emergency personnel, remote sensors, and others use Tesla’s discovery of wireless power. Wireless power transmission (WPT) has the potential to be a common source of consumable energy, but it will only receive serious consideration if the transmit and receive systems are extremely efficient and capable of delivering usable amounts of power. Research has been conducted to improve the efficiency and performance of nearly every aspect of WPT systems, but the relatively new field of metamaterials (MTMs) has yet to play a dominate role in improving system performance. A gradient index (GRIN) MTM lens was designed using Ansoft’s High Frequency Structure Simulator (HFSS) to improve antenna gain and thereby increase WPT system performance. A simple WPT demonstration system using microstrip patch antennas (MPAs) confirmed the benefits of the GRIN MTM lens. The WPT demonstration system, MPAs, and GRIN MTM lens were constructed and experimentally tested near 2.45 GHz. The theoretical and experimental gain improvement of the MPA due to the GRIN MTM lens is 5.91 dB and 7.06 dB, respectively.
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Guelber, Elise Fraga. « Aplicação de células metamateriais em antenas planares ». reponame:Repositório Institucional da UFABC, 2016.
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Orientador: Prof. Dr. Carlos Eduardo CapovillaDissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Elétrica, 2016.
A tecnologia metamaterial vem sendo estudada cientificamente e suas propriedades prometem efeitos inovadores em suas aplicações. A possibilidade de manipular o comportamento eletromagnetico em um dispositivo cercado por metamateriais abre portas para a criação e otimização de novos dispositivos. Qualquer sistema que envolva dispositivos de microondas, optica e antenas, está na grade dos beneficiados por essa tecnologia. As principais caracteristicas dos metamateriais são a refração negativa e as caracteristicas intrinsecas do material com valores negativos. Assumindo esse cen'ario, nesse trabalho ser'a projetada uma célula metamaterial inspirada no conceito de lente de Lenz, que permite uma amplificação do fluxo de energia magnética na região central da estrutura. Essa célula será reconfigurada para sua implementação na estrutura de antenas planares, operando na faixa de 2,4 GHz. Tr¿es modelos de antenas são utilizadas nesse estudo, uma quasi-Yagi , uma PIFA e completando a teoria um arranjo com três PIFAs. A disposição das celulas é feita de forma periódica e estrão, assim como diagramas de radiação extraidos das simulações e testes experimentais. As conclusões são obtidas com referência nesses resultados e por meio de comparações das configurações das antenas com e sem as celulas metamateriaias em sua estrutura.
The metamaterial technology has been studied scientifically and its properties promise innovative effects in their applications. The possibility of manipulating the electromagnetic behavior on a device surrounded by metamaterials opens doors for the creation and optimization of new devices. Any system that involves microwave devices, optics and antennas is on the grid of those benefited by this technology. The main characteristics of the metamaterials are the negative refraction and the intrinsic characteristics of the material with negative values. Assuming this scenario, in this work will be projected a metamaterial cell inspired by the concept of Lenz lens, which allows an amplification of the magnetic flux in the central region of the structure. This cell will be reconfigured for its implementation in the planar antenna structure, operating in the 2.4 GHz range. Three antennas are used in this study, a quasi-Yagi, a PIFA and completing the theory a PIFA array with three elements. The arrangement of the cells is made periodically and strategically in the antenna structure, aiming for improvements in its performance. The characterization of these antennas is carried out by means of reflection and transmission parameters, as well as radiation diagrams extracted from the simulations and experimental tests. The conclusions are achieved with reference in these results and through comparisons of the antenna configurations with and without the metamaterial cells in their structure.
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Měcháček, Radek. « Studie šíření širokospektrých signálů nehomogenním prostředím ». Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218407.
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Work is focused on both theoretical knowledge of the electromagnetic field and the specific properties of metamaterials measured. First, be informed about the fundamentals of electromagnetic fields, the issue of periodic structures to the properties required metastructures. Further experimental work is designed to measure the properties of metamaterials. The measurements will be used as harmonic signals and broadband signals in the frequency range 100MHz to 10GHz. In the last part of the proposed work is carried out experimental work and are evaluated some characteristics of the antennas and measurement of the selected sample.
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Manktelow, Kevin Lee. « Dispersion analysis of nonlinear periodic structures ». Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51936.
Texte intégralRésumé :
The present research is concerned with developing analysis methods for analyzing and exploring finite-amplitude elastic wave propagation through periodic media. Periodic arrangements of materials with high acoustic impedance contrasts can be employed to control wave propagation. These systems are often termed phononic crystals or metamaterials, depending on the specific design and purpose. Design of these systems usually relies on computation and analysis of dispersion band structures which contain information about wave propagation speed and direction. The location and influence of complete (and partial) band gaps is a particularly interesting characteristic. Wave propagation is prohibited for frequencies that correspond to band gaps; thus, periodic systems behave as filters, wave guides, and lenses at certain frequencies. Controlling these behaviors has typically been limited to the manufacturing stage or the application of external stimuli to distort material configurations. The inclusion of nonlinear elements in periodic unit cells offers an option for passive tuning of the dispersion band structure through amplitude-dependence. Hence, dispersion analysis methods which may be utilized in the design of nonlinear phononic crystals and metamaterials are required. The approach taken herein utilizes Bloch wave-based perturbation analysis methods for obtaining closed-form expressions for dispersion amplitude-dependence. The influence of material and geometric nonlinearities on the dispersion relationship is investigated. It is shown that dispersion shifts result from both self-action (monochromatic excitation) and wave-interaction (multi-frequency excitation), the latter enabling dynamic anisotropy in periodic media. A particularly novel aspect of this work is the ease with which band structures of discretized systems may be analyzed. This connection enables topology optimization of unit cells with nonlinear elements. Several important periodic systems are considered including monoatomic lattices, multilayer materials, and plane stress matrix-inclusion configurations. The analysis methods are further developed into a procedure which can be implemented numerically with existing finite-element analysis software for analyzing geometrically-complex materials.
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Kadic, Muamer. « Metamaterials for surface plasmons ». Thesis, Aix-Marseille 3, 2011. http://www.theses.fr/2011AIX30026.
Texte intégralRésumé :
Le travail présenté dans cette thèse comporte différents attrayant sujetsde l'optique comme les métamatériaux, l’optique transformationnelle, lescristaux photoniques, la réfraction négative et les interactions thermoplasmoniques.Nous avons développé plusieurs métamatériaux pour les plasmons desurface basés sur l'optique de transformation. Tout d'abord, nous avonsdémontré théoriquement, numériquement et expérimentalement certainsdispositifs mettant en scène le phénomène d’invisibilité.Deuxièmement, nous avons démontré la réfraction négative des plasmonsde surface en utilisant le concept d'espace de pliage (space folding) pourdes lentilles plates et anisotropes et enfin avec seulement desmétamatériaux diélectriques. Additionnellement, nous avons démontréqu’un damier structuré de films d'or peut exhiber une transmission extraordinairesur toute la gamme de fréquences visible.Enfin, nous avons étudié un problème multiphysique en mixant l'optiqueet thermique et leurs effets induits. Nous avons pu montrer que joueravec l'amplitude d'une onde électromagnétique ou une impulsion, peutinduire un gradient de température et le contrôle parfait d’un tel dispositifthermo-plasmoniqueThe work which has been presented in this thesis includes differentappealing subjects of optics such as metamaterials, transformationaloptics, photonic crystals, negative refraction and thermo-plasmonicinteractions. In this manuscript we have developed several metamaterialsfor Surface Plasmon Polaritons based on the transformational optics.Firstly we have demonstrated theoretically, numerically andexperimentally some SPP cloaking devices. Secondly, we havedemonstrated SPP negative refraction using the concept of space foldingthen with some dielectric metamaterial, flat and anisotropic SPP lenses.Additionaly we have demonstrated that subwavelength checkerboardstructured thick gold films have demonstrated an extra-ordinarytransmission over the visble range of frequencies.Finally, we have investigated a general multiphysics problem to mix opticsand thermally induced effects. We have been able to show that playingwith the amplitude of an electromagnetic wave or a pulse, we can inducea gradient of temperature and control heat of a plasmonic device
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Papakostas, Aris. « Planar chiral optical metamaterials ». Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444955.
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Barr, Lauren. « Giving metamaterials a hand ». Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34561.
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The focus of this thesis is the interaction of electromagnetic fields with chiral structures in the microwave regime. Through this study, which focuses on three regimes of electromagnetic interactions, I aim to develop a deeper understanding of the consequences and manifestations of chiral interactions The structures are on the order of, or smaller than, the wavelength of the probing radiation. As the structures are chiral, they have broken inversion symmetry, and exist in two states where one is the mirror image of the other. The results in this thesis can have impacts on future optical communications technologies and methods of sensing biological molecules. To begin with, the manipulation of the circular polarisation of a propagating beam by bilayer chiral metasurfaces is investigated. The metasurfaces consist of two layers of stacked crosses with a twist between top and bottom layers, forming chiral metamolecules. A broad frequency region of dispersionless polarisation rotation appears between two resonances, due to alignment between electric and magnetic dipoles. The dependence of this effect on the layer separation is studied for two similar metasurfaces. Evanescent chiral electromagnetic fields are the focus of the next chapter. An array of chiral antennas produces chiral near-fields at their resonant frequency. Aligned and subwavelength helices placed within this field interact differently depending on the handedness of the field with respect to the handedness of the helices. This difference in interaction strength is measured for the helices and an effective medium model where multipolar interactions are forbidden. Comparison of these two systems leads to the conclusion that the contribution to a chiral interaction from multipolar modes is minimal, in contrast to previous publications. The third study concentrates on the electromagnetic wave bound to an "infinitely long" metal helix. The helix has infinite-fold screw symmetry, and this leads to interesting features in the energy-dispersion of the waves it supports. The broad frequency range of high, tunable, dispersionless index is interpreted using a geometrical approach, and the factors that limit the bandwidth explained. A modified geometry is suggested for increased bandwidth. The final part of the thesis is dedicated to future work, based on the results presented thus far. Three suggestions for future study are presented, including chiroptical signals from higher-order chiral arrangements, the effect of reflecting surfaces next to chiral objects and the possible use of orbital angular momentum for chiroptical measurements.
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Williams, Christopher. « Teraherts waveguiding on metamaterials ». Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520384.
Texte intégralRésumé :
Terahertz time-domain spectroscopy (TTDS) is a powerful spectroscopic technique, combining pulsed broadband operation with high sensitivity coherent detection at room temperature. This thesis describes studies of terahertz surface plasmon polariton (SPP) guidance on a range of metamaterial structures using TTDS. Metamaterials are artificial media constructed from sub-wavelength dimension conducting elements which have an electromagnetic response that can be engineered by creating geometrical plasma-like resonances. In this work, high-confinement terahertz waveguiding is achieved by binding SPPs to cavity resonances which spoof the behaviour of intrinsic surface plasmon resonances found at much higher frequencies. The main aim of these studies is to investigate their properties with regard to potential applications in waveguiding and sensing. The first two chapters of this thesis describe the background to the subject. In chapter 3, the construction of a novel, flexible geometry, fibre-coupled TTDS system using hollow-core photonic crystal fibre (HC-PCF) is described. The extension of the system to include a near-field probe for evanescent field characterisation is also discussed. In chapter 4, we present the first direct observation of terahertz SPP propagation on plasmonic metamaterials consisting of copper sheets patterned with two-dimensional arrays of square copper-lined holes. Wavelength-scale field confinement is experimentally observed over an octave in frequency close to the band edge, representing a two order of magnitude increase in confinement compared to a flat metal sheet. In chapter 5, metamaterials consisting of two-dimensional arrays of coaxial apertures are shown to support two spoof plasmon modes below the band edge, enabling wavelength-scale field confinement to be experimentally realised at two distinct frequencies. In chapter 6, we present the first experimental results for terahertz SPP propagation on helical and discretely grooved cylindrical metamaterials termed metawires. In each case the results are compared with numerical simulations.
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Dubrovina, Natalia. « Metamaterials for photonic applications ». Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112088/document.
Texte intégralRésumé :
L’objet de cette étude concerne l’exploration, à la fois sur le plan théorique et expérimental, de la possibilité d’utilisation des métamatériaux pour des applications dans le domaine de la photonique aux longueurs d’onde télécoms (λ=1.5µm). L’un des principaux objectifs adressés dans le cadre de la thèse est de réaliser l’ingénierie de l’indice effectif en utilisant des résonances des plasmons de surface localisés des métamatériaux métallo-diélectriques. Deux cas particulièrement importants du point de vue de la réalisation technologique sont considérés :• Propagation en espace libre quand une onde lumineuse sous incidence normale ou oblique interagit avec une surface diélectrique recouverte d’une monocouche de métamatériaux.• Propagation dans une configuration guide d’onde avec une monocouche de métamatériaux à la surface d’un guide d’onde en Silicium.Les résultats des modélisations et des mesures expérimentales montrent que les propriétés optiques d’une mono-couche de métamatériau peuvent être décrites par celle d’une couche homogène avec un certain indice effectif. L’épaisseur de cette couche est égale à celle des motifs métalliques, à condition qu’elle soit inférieure à quelques dizaines de nm. Pour des faibles facteurs de remplissage en surface, l’indice de réfraction d’une telle couche suit l’approximation de Maxwell-Garnett. Cet indice effectif ne dépend pas de l’angle d’incidence ni de l’orientation de la polarisation de la lumière (perpendiculaire ou dans le plan d’incidence). Au voisinage de la fréquence de résonance pour un facteur de remplissage de métamatériau de 20% en surface on obtient un indice de réfraction très élevé : neff=10. Cet indice de réfraction est plusieurs fois supérieur à celui qu’on trouve dans des matériaux naturels. L’adaptation de cette approche à configuration guidée à utiliser une structure hybride composée d’une couche de métamatériau à la surface d’un guide d’onde en Silicium. Les travaux réalisés ont permis de démontrer la possibilité d’effectuer l’ingénierie de l’indice effectif et de contrôler le niveau des pertes d’un tel guide d’onde hybride en utilisant des métamatériau métallo-diélectriques à base des fils d’Au de 200X50X50nm. Le contraste d’indice au voisinage de la ligne de la résonance donné par des modélisations et confirmé expérimentalement est de ±1.5, soit plus que ce que l’on peut obtenir avec un guide Silicium gravé. Ce résultat représente une première démonstration sur le plan international de fonctionnement des métamatériaux en configuration guidée.De plus, en contrôlant l’orientation des motifs de métamatériaux, on peut réaliser un indice anisotrope. Les résultats obtenus ouvrent des perspectives très prometteuses pour la réalisation de dispositifs en optique guidée utilisant les transformations d’espaceThe subject of the PhD thesis deals with metamaterials for photonic applications. The main objective is to investigate the potential of metallic metamaterials for building optical functions at NIR optical frequencies. A significant part of the work is focused on the engineering of the metamaterials effective index associated with localized plasmon resonances. Two configurations of particular importance for fabrication technology are considered:• Free space light propagation, with the incident electromagnetic wave interacting with single metafilms at either normal or oblique incidence. • Guided wave configuration, with single metamaterial layer placed on top of dielectric waveguide.For the free space configuration, the validity of the effective medium approach was investigated both numerically and experimentally with the example of metamaterials composed of either gold cut wires or split ring resonators and continuous wires on silicon substrate. On the basis of these examples it was shown that the metafilm behavior is indeed analogous to that of a homogeneous layer. The thickness of this layer is that of the deposited metal. The validity of this conclusion was verified with respect to a number of criteria consistent with the Maxwell-Garnett approximation. It was shown in particular that near the resonance frequency the effective index of the metafilm layer can reach very high values neff=10 that cannot be attained with natural materials.The effective medium approach developed for a single metamaterial layer in free space configuration was further extended to a guided wave configuration. The objective is to achieve an efficient control over the flow of light in the waveguide using effective index variations induced by metamatarial resonances. The possibility of achieving a significant effective index variation with a silicon slab waveguide covered by 200X50X50nm cut wires was investigated by numerical modeling and confirmed by experimental results. The magnitude of local index variation in the vicinity of the resonance frequency deduced from experimental data is as high as ±1.5. The possibility for controlling the local effective index at the nanoscale can be used in transformation optics applications. The hybrid metamaterial guided wave configuration may become a promising alternative to the bulk multi-layers metamaterial structures in the near infrared domain
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Karvounis, Artemios. « All dielectric reconfigurable metamaterials ». Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/424497/.
Texte intégralRésumé :
This thesis reports on my research efforts towards all-dielectric metamaterials with reconfigurable functionalities: • I have reported the first optomechanical nonlinear dielectric metamaterial. I have shown that such metamaterials provide extremely large optomechanical nonlinearities at near infrared, operating at intensities of only a few μW per unit cell and modulation frequencies as high as 152 MHz, thereby offering a path to fast, compact, and energy efficient all-optical metadevices. • I have experimentally demonstrated the first all-dielectric electro-optical nanomechanical modulator based on all-dielectric nanomembrane metamaterial. Furthermore, I have shown the dynamical control of optical properties of this device, with modulation frequency up to 7 MHz. I have also establish an encapsulation technique where any nano-membrane can be embedded within a fiber setup with electrical feedthroughs and pressure control. • I have studied for first time the optical properties of Diamond nano-membrane metamaterials. Diamond membranes after nanostructuring with Focus Ion Beam, present broadband, polarization-independent absorption that can be used as efficient coherent absorbers for optical pulses as short as 6 fs. This novel class of metamaterials have been used for coherent modulation with modulation contrast up to 40% at optical fluences of few nJ/cm2 across the visible spectrum. • I have reported the first optically-switchable, all-chalcogenide phase-change metamaterial. Germanium antimony telluride alloys (GST) after nanostructuring subwavelength-thickness films of GST present high-quality resonances that are spectrally shifted by laser-induced structural transitions, providing reflectivity and transmission switching contrast ratios of up to 5:1 (7 dB) at near-infrared wavelengths selected by design, or strong colour contrast in visible due to its plasmonic nature. • This work has introduced dielectric nano-membrane metamaterials, as a platform to provide optically switchable, nonlinear, reconfigurable responses. Due to nanomechanical actuation based on optical/electromagnetic forces, coherent modulation based on the diamond absorbers and phase change media of Chalcogenide glasses.
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ElKabbash, Mohamed. « ACTIVE PLASMONICS AND METAMATERIALS ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1512659080056302.
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Zedler, Michael. « Systematic topological design of metamaterials : scalar and vectorial 3D metamaterials and their realisation ». kostenfrei, 2008. http://mediatum2.ub.tum.de/doc/653119/653119.pdf.
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Prat, Camps Jordi. « Shaping magnetic felds with superconductor-metamaterial hybrids ». Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/309138.
Texte intégralRésumé :
El magnetisme és molt important en diverses àrees de la ciència i la tecnologia, cobrint un rang molt ampli d'escales i temes. En aquesta tesis presentem el desenvolupament teòric i la realització experimental de diversos dispositius nous pel control dels camps magnètics. Pel disseny d'aquests s'han emprat diverses estratègies; la teoria de l'òptica de transformació s'ha combinat amb resultats obtinguts directament de les equacions de Maxwell, i les propostes idealitzades han esdevingut dispositius reals mitjançant la combinació de materials ferromagnètics i superconductors formant diferents metamaterials magnètics.
En primer lloc presentem l'estudi referent a les capes invisibilitat magnètica. De manera anàloga a com actuaria una capa d'invisibilitat per llum visible, una capa d'invisibilitat magnètica evita que els camps penetrin al seu interior al mateix temps que la capa i el seu contingut són magnèticament indetectables des de l'exterior. En aquesta tesis presentem el desenvolupament de diferents dissenys de capa d'invisibilitat, centrant-nos en un sistema bicapa superconductor-ferromagnètic. Aquesta bicapa ha estat construïda i provada amb èxit.
La concentració de camps magnètics també ha estat estudiada. Hem dissenyat una capa concentradora magnètica cilíndrica, la qual concentra els camps magnètics aplicats externs en el seu orifici interior. Alhora, aquesta mateixa capa expulsa el camp magnètic cap a l'exterior quan la font de camp se situa a l'orifici interior. S'han fabricat algunes d'aquestes capes concentradores emprant materials superconductors i ferromagnètics i les seves propietats s'han verificat experimentalment. A més a més també hem demostrat que les capes permeten incrementar l'acoblament magnètic entre circuits. Aquesta propietat l'hem aplicat experimentalment per demostrar que les capes concentradores permeten millorar la transmissió d'energia elèctrica sense fils.
Seguidament hem estudiat la transmissió de camps magnètics. A diferència de les ones electromagnètiques que es propaguen fàcilment dins de guies d'ones o fibres òptiques, els camps magnètics decauen ràpidament a mesura que ens allunyem de la font. A fi de superar aquesta limitació hem desenvolupat un sistema de "mànega magnètica" que permet la transferència de camps magnètics estàtics fins a llargues distàncies i que es pot construir combinant adequadament capes superconductores i ferromagnètiques. El disseny l'hem validat a partir de simulacions numèriques i desenvolupaments analítics. Algunes "mànegues" s'han fabricat i les seves propietats ha estat experimentalment demostrades.
Finalment hem desenvolupat un forat de cuc magnètic. Inspirats pels forats de cuc cosmològics, que connecten dos punts de l'espai a través d'un camí que se situa fora de l'espai tridimensional convencional, hem desenvolupat un dispositiu capaç de crear l'efecte equivalent per camps magnètics estàtics. Així, el forat de cuc magnètic connecta magnèticament dos punts de l'espai a través d'un camí que és magnèticament indetectable. El dispositiu està format per una "mànega magnètica" recoberta d'una esfera superconductora i una "metasuperfície" ferromagnètica. Les seves propietats han estat estudiades teòricament i el dispositiu ha estat construït. Això ha permès demostrar, també, les seves característiques de manera experimental.
En resum, aquesta tesis conté el desenvolupament teòric i la realització experimental de diversos dispositius que permeten la manipulació de camps magnètics. A banda d'estudiar diversos problemes concrets com la invisibilitat magnètica, la concentració o la transmissió de camps, la present recerca ha donat lloc a tot un conjunt d'"eines" que permeten el control i la manipulació de camps magnètics d'una manera general.Magnetism is very important in various areas of science and technology, covering a wide range of scales and topics. In this thesis we present the theoretical development and the experimental realization of various novel devices to control magnetic fields. Their design is based on different strategies; transformation optics theory is combined with solutions directly obtained from Maxwell equations, and ideal designs are turned into real devices combining superconducting and ferromagnetic materials forming different magnetic metamaterials. We first study the cloaking of magnetic fields. Analogous to the concept of an "invisibility" cloak for light, a cloak for static magnetic fields prevents fields to penetrate in its interior and makes the cloak itself and its content magnetically undetectable from the exterior. Different designs of magnetic cloak are developed and a bilayer superconductor-ferromagnetic cylindrical cloak is experimentally built and tested. The concentration of magnetic fields is also addressed. A cylindrical magnetic concentrating shell is designed, demonstrating that it concentrates external fields in its interior hole and it also expels the field of internal sources towards the exterior. Different concentrating shells are experimentally built using superconducting and ferromagnetic materials and their properties are validated. We also demonstrate that concentrating shells increase the magnetic coupling between circuits. We apply this property to experimentally demonstrate they enhance the wireless transfer of power. The transfer of static magnetic fields is also studied. Different from electromagnetic waves that easily propagate in waveguides or optical fibers, magnetic fields rapidly decay as one moves far from the source. To overcome this limitation we develop the magnetic hose, a design that allows to transfer static magnetic fields to arbitrary distances and can be realized with an adequate combination of superconducting and ferromagnetic shells. The design is validated using numerical calculations and analytical developments. Some hoses are experimentally built and their properties are demonstrated. Finally we develop a magnetic wormhole. Inspired by cosmological wormholes, that connect two points in space through a path that is out of the conventional 3D space, we study an analogous effect for static magnetic fields. The magnetic wormhole magnetically connects two points in space through a path that is magnetically undetectable. It is composed of an interior magnetic hose surrounded by a spherical superconducting shell and a spherical ferromagnetic metasurface. An actual magnetic wormhole is experimentally built and its properties are demonstrated. To sum up, this thesis contains the theoretical development and the experimental realization of different devices to manipulate magnetic fields. In addition to addressing different particular problems, like magnetic cloaking, concentration or magnetic field transfer, this research has resulted in a whole set of new "tools" to shape and control static magnetic fields in a general way.
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King, Neil James. « Aspects of metamaterial structures : theory and simulation ». Thesis, University of Salford, 2007. http://usir.salford.ac.uk/26761/.
Texte intégralRésumé :
The investigations reported here address the issue of overcoming loss in a typical isotropic metamaterial. The possibility of adding functionality to such materials, through gyrotropic effects, and diffraction management of nonlinear beams, driven by negative phase accumulation, is presented. Loss is overcome by the introduction of gain to the metamaterial. This is achieved on the basis that typical split-ring metaparticles can be suitably enhanced through the addition of carefully selected diodes. The detailed analysis given here deploys a familiar equivalent circuit model and specific current-voltage characteristics. It is emphasised that conditions must be in place to ensure overall stable material behaviour. The methodology uses convective and absolute instability concepts and it is shown that the latter can be so detrimental as to lead to a much reduced frequency window of operation. Another set of investigations emphasises that surface waves provide a path to new science. Consequently the propagation of surface waves along the interface between a metamaterial and a gyrotropic medium is promising for applications. The investigation outcomes of this complicated system need to demonstrate generation properties in real time. Hence, some unique finite-difference time-domain (FDTD) computations have been developed enabling their interesting connection to the Goos- Hanchen shift to be elegantly displayed. Many interesting forms of surface waves are discussed including the simultaneous generation of TE and TM waves propagating in opposite directions. It is well known that in an isotropic metamaterial backward waves can exist so this property is exploited to create a fascinating form of diffraction management. This is investigated both for the bulk and for cavities and the impact of what is defined as nonlinear diffraction is introduced. Finally, some magnetooptics is introduced that adds even more functionality to the generation of cavity solitons.