21 |
Modelovn kmitoÄtovÄ selektivnch povrch v programu COMSOL Multiphysics / Modeling frequency selective surfaces in COMSOL MultiphysicsH¶hn, Tom January 2008 (has links)
Metoda koneÄnch prvk implementovan v programu COMSOL Multiphysics je vyuvna k analze tzv. free-standing kmitoÄtovÄ selektivnch povrch ve 3D. Tyto modely jsou nslednÄ doplnÄny o periodick© okrajov© podmnky. Dle jsou free-standing povrchy doplnÄny o vrstvy dielektrika a je zkoumn jejich vliv na modul Äinitele odrazu. V analytick© Ästi jsou vyhodnoceny vlivy poÄtu element diskretizaÄn mky na pesnost vsledku a d©lku vpoÄt. Vsledky jsou srovnvny vzhledem k vsledkm uvedenm v literatue [5]. V zvÄreÄn© Ästi prce je vysvÄtlen postup pi generovn m-file pro obd©lnkov element a pouit globlnho optimalizaÄnho algoritmu PSO, kter automaticky upravuje rozmÄry vodiv©ho motivu tak, aby bylo dosaeno prbÄhu modulu Äinitele odrazu podle poadovan©ho prbÄhu.
|
22 |
Spectral Signature Modification By Application Of Infrared Frequency-selective SurfacesMonacelli, Brian 01 January 2005 (has links)
It is desirable to modify the spectral signature of a surface, particularly in the infrared (IR) region of the electromagnetic spectrum. To alter the surface signature in the IR, two methods are investigated: thin film application and antenna array application. The former approach is a common and straightforward incorporation of optically-thin film coatings on the surface designated for signature modification. The latter technique requires the complex design of a periodic array of passive microantenna elements to cover the surface in order to modify its signature. This technology is known as frequency selective surface (FSS) technology and is established in the millimeter-wave spectral regime, but is a challenging technology to scale for IR application. Incorporation of thin films and FSS antenna elements on a surface permits the signature of a surface to be changed in a deterministic manner. In the seminal application of this work, both technologies are integrated to comprise a circuit-analog absorbing IR FSS. The design and modeling of surface treatments are accomplished using commercially-available electromagnetic simulation software. Fabrication of microstructured antenna arrays is accomplished via microlithographic technology, particularly using an industrial direct-write electron-beam lithography system. Comprehensive measurement methods are utilized to study the patterned surfaces, including infrared spectral radiometry and Fourier-transform infrared spectrometry. These systems allow for direct and complementary spectral signature measurements--the radiometer measures the absorption or emission of the surface, and the spectrometer measures its transmission and reflection. For the circuit-analog absorbing square-loop IR FSS, the spectral modulation in emission is measured to be greater than 85% at resonance. Other desirable modifications of surface signature are also explored; these include the ability to filter radiation based on its polarization orientation and the ability to dynamically tune the surface signature. An array of spiral FSS elements allows for circular polarization conditioning. Three techniques for tuning the IR FSS signature via voltage application are explored, including the incorporation of a pn junction substrate, a piezoelectric substrate and a liquid crystal superstrate. These studies will ignite future explorations of IR FSS technology, enabling various unique applications.
|
23 |
Development of Optically Selective Plasmonic Coatings : Design of experiment (DoE) approach to develop the effect of plasmonic materials on selective surfacesKhaled, Fatima January 2024 (has links)
Absolicon is a pioneering solar technology development company specializing in the manufacturing and selling of advanced solar energy systems engineered to generate renewable energy for diverse use. Comprising essential components such as reflectors (mirrors) and a solar receiver tube, these solar energy systems are equipped to efficiently capture and convert solar irradiation into usable thermal energy. As an integral facet of an ongoing research, this project will contribute to optimize the reflection and absorption capacity in receiver tubes of Absolicon's solar collectors. The aim is to investigate optically selective plasmonic coatings intended as an undercoating in the solar selective surfaces. The main coating material that will be used and analysed is gold due to its plasmonic properties and inert nature as well as its low toxicity. The gold will be coated on stainless steel using physical vapor deposition (PVD) and then annealed at mid-to-high temperatures to produce a plasmonic surface. The effect of Au thicknesses, annealing times/temperature and will be investigated to optimize the coating with regards to optical properties based on a systematic method called Design of Experiments (DoE). The goal for the gold coating is to increase the reflectance in the infrared region while generating a plasmonic absorption peak in the visible region (the position and width will be optimized), making it a more beneficial surface to coat a solar selective surface than the original stainless steel (SS). It was found that the size and inter-particle distance of GNPs depend on the temperature and annealing time for different thickness. The surface analysis from SEM-images and AFM-topographs provided that samples with smaller grains are more likely to exhibit significant plasmonic effects compared to larger grains. According to the surface characterization, either thinner gold coating exposed to high temperature for short annealing time or thicker gold coating with longer annealing time provide plasmonic absorption peak in visible light region.
|
24 |
Modélisation électromagnétique des Surfaces Sélectives en Fréquence finies uniformes et non-uniformes par la Technique de Changement d'Echelle (SCT) / Electromagnetic modeling of finite uniform and non-uniform frequency selective surfaces using Scale Changing Technique (SCT)Tchikaya, Euloge Budet 22 October 2010 (has links)
Les structures planaires de tailles finies sont de plus en plus utilisées dans les applications des satellites et des radars. Deux grands types de ces structures sont les plus utilisés dans le domaine de la conception RF à savoir Les Surfaces Sélectives en Fréquence (FSS) et les Reflectarrays. Les FSSs sont un élément clé dans la conception de systèmes multifréquences. Elles sont utilisées comme filtre en fréquence, et trouvent des applications telles que les radômes, les réflecteurs pour antenne Cassegrain, etc. Les performances des FSSs sont généralement évaluées en faisant l'hypothèse d'une FSS de dimension infinie et périodique en utilisant les modes de Floquet, le temps de calcul étant alors réduit quasiment à celui de la cellule élémentaire. Plusieurs méthodes permettant la prise en compte de la taille finie des FSSs ont été développées. La méthode de Galerkin basée sur l'approche rigoureuse permet la prise en compte des interactions entre les différents éléments du réseau, mais cette technique ne fonctionne que pour les FSSs de petite taille, typiquement 3x3 éléments. Pour les grands réseaux, cette méthode n'est plus adaptée, car le temps de calcul et l'exigence en mémoire deviennent trop grands. Donc, une autre approche est utilisée, celle basée sur la décomposition spectrale en onde plane. Elle permet de considérer un réseau fini comme un réseau périodique infini, illuminé partiellement par une onde plane. Avec cette approche, des FSSs de grande taille sont simulées, mais elle ne permet pas dans la plupart des cas, de prendre en compte les couplages qui existent entre les différentes cellules du réseau, les effets de bord non plus. La simulation des FSSs par les méthodes numériques classiques basées sur une discrétisation spatiale (méthode des éléments finis, méthode des différences finies, méthode des moments) ou spectrale (méthodes modales) aboutit souvent à des matrices mal conditionnées, des problèmes de convergence numérique et/ou des temps de calcul excessifs. Pour éviter tous ces problèmes, une technique appelée technique par changements d'échelle tente de résoudre ces problèmes. Elle est basée sur le partitionnement de la géométrie du réseau en plusieurs sous-domaines imbriqués, définis à différents niveaux d'échelle du réseau. Le multi-pôle de changement d'échelle, appelé Scale-Changing Networks (SCN), modélise le couplage électromagnétique entre deux échelles successives. La cascade de ces multi-pôles de changement d'échelle, permet le calcul de la matrice d'impédance de surface de la structure complète et donc la modélisation globale du réseau. Ceci conduit à une réduction significative en termes de temps de calcul et d'espace mémoire par rapport aux méthodes numériques classiques. Comme le calcul des multi-pôles de changement d'échelle est mutuellement indépendant, les temps d'exécution peuvent encore être réduits de manière significative en parallélisant le calcul. La SCT permet donc de modéliser des FSSs Finies tout en prenant en compte le couplage entre les éléments adjacents du réseau. / The finite size planar structures are increasingly used in applications of satellite and radar. Two major types of these structures are the most used in the field of RF design ie Frequency Selective Surfaces (FSS) and the Reflectarrays. The FSSs are a key element in the design of multifrequency systems. They are used as frequency filter, and find applications such as radomes, reflector Cassegrain antenna, etc.. The performances of FSSs are generally evaluated by assuming an infinite dimensional FSS using periodic Floquet modes, the computation time is then reduced almost to that of the elementary cell. Several methods have been developed for taking into account the finite dimensions of arrays. For example the Galerkin method uses a rigorous element by element approach. With this method, the exact interactions between the elements are taken into account but this technique works only for small FSS, typically 3x3 elements. For larger surfaces, this method is no more adapted. The computation time and the memory requirement become too large. So another approach is used based on plane wave spectral decomposition. It allows considering the finite problem as a periodic infinite one locally illuminated. With this approach, large FSS are indeed simulated, but the exact interactions between the elements are not taken into account, the edge effects either. The simulation of FSS by conventional numerical methods based on spatial meshing (finite element method, finite difference, method of moments) or spectral (modal methods) often leads in the practice to poorly conditioned matrices, numerical convergence problems or/and excessive computation time. To avoid these problems, a new technique called Scale Changing Technique attempts to solve these problems. The SCT is based on the partition of discontinuity planes in multiple planar sub-domains of various scale levels. In each sub- omain the higher-order modes are used for the accurate representation of the electromagnetic field local variations while low-order modes are used for coupling the various scale levels. The electromagnetic coupling between scales is modelled by a Scale Changing Network (SCN). As the calculation of SCN is mutually independent, the execution time can still be significantly reduced by parallelizing the computation. With the SCT, we can simulate large finite FSS, taking into account the exact interactions between elements, while addressing the problem of excessive computation time and memory
|
25 |
Radômes actifs utilisant des matériaux et structures à propriétés électromagnétiques contrôléesLunet, Guillaume 28 October 2009 (has links)
Les recherches que nous présentons dans ce mémoire s'inscrivent dans le cadre du développement de nouvelles structures et de l'étude de matériaux accordables en vue d'une intégration industrielle comme radôme actif.Plus particulièrement, ils consistent en la réalisation d'un dispositif micro-onde permettant à la fois un filtrage et une agilité fréquentiels en espace libre. Des structures basées sur des surfaces sélectives en fréquences, pour l'aspect filtrage, et sur des matériaux de type ferroélectrique, pour l'aspect accordabilité, sont développées. Des modélisations et des simulations électromagnétiques montrent que le changement de permittivité du matériau, obtenu par application d'un champ électrique externe, permet le pilotage fréquentiel de la transmission de la structure. Une mise en oeuvre expérimentale complète ces travaux, au cours de laquelle des prototypes ont été fabriqués par des techniques de photolithographie, puis caractérisés en espace libre grâce à un banc ABmm. Les mesures micro-ondes valident ainsi les résultats de simulations menées en amont et montrent les possibilités de contrôler la fréquence de transmission du radôme. / The research we present in this memory registers within the framework to develop new structures and to study tunable materials for an industrial integration as an active radome. Specifically, they consist of achieving a free space microwave device for both a filtering behaviour and a frequency agility behaviour. Structures based on frequency selective surfaces, for the filtering aspect, and on ferroelectric materials for the tuning aspect, are developed. Modeling and simulations show that the change of the material permittivity, obtained by applying an external electric field, enable piloting the transmission frequency of the structure. An experimental implementation complete this work and prototypes have been fabricated by photolithography techniques and then characterized in free space with a bench ABmm. Thus, microwave measurements validate the results of simulations and show the possibility to control the frequency transmission of the radome.
|
26 |
An?lise e otimiza??o de superf?cies seletivas de Frequ?ncia utilizando redes neurais artificiais e algoritmos de otimiza??o naturalCruz, Rossana Moreno Santa 28 September 2009 (has links)
Made available in DSpace on 2014-12-17T14:54:53Z (GMT). No. of bitstreams: 1
RossanaMSC.pdf: 3237270 bytes, checksum: 01cfb4de4da5c1c94fba895ebbbdddb1 (MD5)
Previous issue date: 2009-09-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The bidimensional periodic structures called frequency selective surfaces have been well investigated because of their filtering properties. Similar to the filters that work at the
traditional radiofrequency band, such structures can behave as band-stop or pass-band filters, depending on the elements of the array (patch or aperture, respectively) and can be
used for a variety of applications, such as: radomes, dichroic reflectors, waveguide filters, artificial magnetic conductors, microwave absorbers etc. To provide high-performance
filtering properties at microwave bands, electromagnetic engineers have investigated various types of periodic structures: reconfigurable frequency selective screens,
multilayered selective filters, as well as periodic arrays printed on anisotropic dielectric substrates and composed by fractal elements. In general, there is no closed form solution
directly from a given desired frequency response to a corresponding device; thus, the analysis of its scattering characteristics requires the application of rigorous full-wave
techniques. Besides that, due to the computational complexity of using a full-wave simulator to evaluate the frequency selective surface scattering variables, many
electromagnetic engineers still use trial-and-error process until to achieve a given design criterion. As this procedure is very laborious and human dependent, optimization
techniques are required to design practical periodic structures with desired filter specifications. Some authors have been employed neural networks and natural optimization
algorithms, such as the genetic algorithms and the particle swarm optimization for the frequency selective surface design and optimization. This work has as objective the accomplishment of a rigorous study about the electromagnetic behavior of the periodic structures, enabling the design of efficient devices applied to microwave band. For this, artificial neural networks are used together with natural optimization techniques, allowing the accurate and efficient investigation of various types of frequency selective surfaces, in a simple and fast manner, becoming a powerful tool for the design and optimization of such structures / As estruturas planares peri?dicas bidimensionais, conhecidas como Superf?cies Seletivas de Frequ?ncia, t?m sido bastante estudadas por causa da propriedade de filtragem
de frequ?ncia que apresentam. Similares aos filtros que operam na faixa tradicional de radiofrequ?ncia, tais estruturas podem apresentar caracter?sticas espectrais de filtros rejeitafaixa ou passa-faixa, dependendo do tipo de elemento do arranjo (patch ou abertura, respectivamente) e podem ser utilizadas em uma variedade de aplica??es, tais como
radomes, refletores dicr?icos, filtros de micro-ondas, condutores magn?ticos artificiais, absorvedores etc. Para melhorar o desempenho de tais dispositivos eletromagn?ticos e
investigar suas propriedades, muitos estudiosos t?m analisado v?rios tipos de estruturas peri?dicas: superf?cies seletivas de frequ?ncia reconfigur?veis, filtros de m?ltiplas camadas
seletivas, al?m de arranjos peri?dicos impressos sobre substratos diel?tricos anisotr?picos e que utilizam geometrias fractais na sua forma??o. Em geral, n?o existe uma solu??o
anal?tica diretamente extra?da a partir da resposta em frequ?ncia de um dispositivo; desta forma, a an?lise de suas caracter?sticas espectrais requer a aplica??o de t?cnicas de onda completa rigorosas, como o m?todo da equa??o integral, por exemplo. Al?m disso, devido ? complexidade computacional exigida para a implementa??o destes m?todos, muitos estudiosos ainda utilizam a investiga??o por tentativa e erro, para alcan?ar crit?rios satisfat?rios ao projeto dos dispositivos. Como este procedimento ? muito trabalhoso e
dependente do homem, faz-se necess?rio o emprego de t?cnicas de otimiza??o que acelerem a obten??o de estruturas peri?dicas com especifica??es de filtragem desejadas. Alguns autores t?m utilizado redes neurais artificiais e algoritmos de otimiza??o natural, como os algoritmos gen?ticos e a otimiza??o por enxame de part?culas no projeto e otimiza??o das superf?cies seletivas de frequ?ncia. Este trabalho tem como objetivo realizar um estudo mais aprofundado sobre o comportamento eletromagn?tico das estruturas peri?dicas seletivas de frequ?ncia, possibilitando a obten??o de dispositivos eficientes e aplic?veis na faixa de micro-ondas. P ra isto, redes neurais artificiais s?o utilizadas em conjunto com t?cnicas de otimiza??o baseadas na natureza, permitindo a investiga??o precisa e eficiente de v?rios tipos de superf?cies seletivas de frequ?ncia, de forma simples e r?pida, tornando-se, portanto, uma poderosa ferramenta de projeto e otimiza??o de tais estruturas
|
27 |
An?lise e s?ntese de antenas e superf?cies seletivas de frequ?ncia utilizando computa??o evolucion?ria e intelig?ncia de enxamesLins, Hertz Wilton de Castro 11 October 2012 (has links)
Made available in DSpace on 2014-12-17T14:55:06Z (GMT). No. of bitstreams: 1
HertzWCL_TESE.pdf: 4465162 bytes, checksum: b8574ba7e4819cb59386ad0ba99ebd86 (MD5)
Previous issue date: 2012-10-11 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The frequency selective surfaces, or FSS (Frequency Selective Surfaces), are
structures consisting of periodic arrays of conductive elements, called patches, which are
usually very thin and they are printed on dielectric layers, or by openings perforated on
very thin metallic surfaces, for applications in bands of microwave and millimeter
waves. These structures are often used in aircraft, missiles, satellites, radomes, antennae
reflector, high gain antennas and microwave ovens, for example. The use of these
structures has as main objective filter frequency bands that can be broadcast or rejection,
depending on the specificity of the required application. In turn, the modern
communication systems such as GSM (Global System for Mobile Communications),
RFID (Radio Frequency Identification), Bluetooth, Wi-Fi and WiMAX, whose services
are highly demanded by society, have required the development of antennas having, as
its main features, and low cost profile, and reduced dimensions and weight. In this
context, the microstrip antenna is presented as an excellent choice for communications
systems today, because (in addition to meeting the requirements mentioned intrinsically)
planar structures are easy to manufacture and integration with other components in
microwave circuits. Consequently, the analysis and synthesis of these devices mainly,
due to the high possibility of shapes, size and frequency of its elements has been carried
out by full-wave models, such as the finite element method, the method of moments and
finite difference time domain. However, these methods require an accurate despite great
computational effort. In this context, computational intelligence (CI) has been used
successfully in the design and optimization of microwave planar structures, as an
auxiliary tool and very appropriate, given the complexity of the geometry of the antennas
and the FSS considered. The computational intelligence is inspired by natural
phenomena such as learning, perception and decision, using techniques such as artificial
neural networks, fuzzy logic, fractal geometry and evolutionary computation. This work
makes a study of application of computational intelligence using meta-heuristics such as
genetic algorithms and swarm intelligence optimization of antennas and frequency
selective surfaces. Genetic algorithms are computational search methods based on the
theory of natural selection proposed by Darwin and genetics used to solve complex
problems, eg, problems where the search space grows with the size of the problem. The
particle swarm optimization characteristics including the use of intelligence collectively
being applied to optimization problems in many areas of research. The main objective of
this work is the use of computational intelligence, the analysis and synthesis of antennas
and FSS. We considered the structures of a microstrip planar monopole, ring type, and a
cross-dipole FSS. We developed algorithms and optimization results obtained for
optimized geometries of antennas and FSS considered. To validate results were
designed, constructed and measured several prototypes. The measured results showed
excellent agreement with the simulated. Moreover, the results obtained in this study were
compared to those simulated using a commercial software has been also observed an
excellent agreement. Specifically, the efficiency of techniques used were CI evidenced
by simulated and measured, aiming at optimizing the bandwidth of an antenna for
wideband operation or UWB (Ultra Wideband), using a genetic algorithm and
optimizing the bandwidth, by specifying the length of the air gap between two frequency
selective surfaces, using an optimization algorithm particle swarm / As superf?cies seletivas de freq??ncia, ou FSS (Frequency Selective Surfaces), s?o
estruturas constitu?das por arranjos peri?dicos de elementos condutores, denominados
patches, geralmente muito finos e impressos sobre camadas diel?tricas, ou de aberturas,
perfuradas em superf?cies met?licas muito finas, para aplica??es nas faixas de
microondas e ondas milim?tricas. Estas estruturas s?o frequentemente utilizadas em
aeronaves, m?sseis, sat?lites, radomes, antenas de refletor, antenas de alto ganho e fornos
de microondas, por exemplo. A utiliza??o destas estruturas tem como objetivo principal
filtrar bandas de freq??ncia, que podem ser de transmiss?o ou de rejei??o, dependendo
da especificidade da aplica??o desejada. Por sua vez, os sistemas de comunica??o
modernos, tais como GSM (Global System for Mobile Communications), RFID (Radio
Frequency Identification), Bluetooth, Wi-Fi e WiMAX, cujos servi?os s?o altamente
demandados pela sociedade, t?m requerido o desenvolvimento de antenas que
apresentem, como caracter?sticas principais, baixo custo e perfil, al?m de peso e
dimens?es reduzidas. Neste contexto, a antena de microfita se apresenta como uma
excelente op??o para os sistemas de comunica??es atuais, pois (al?m de atenderem
intrinsicamente aos requisitos mencionados) s?o estruturas planares de f?cil fabrica??o e
integra??o com outros componentes de circuitos de microondas. Em consequ?ncia, a
an?lise e principalmente a s?ntese destes dispositivos, em face da grande possibilidade de
formas, dimens?es e periodicidade de seus elementos, tem sido efetuada atrav?s de
modelos de onda completa, tais como o m?todo dos elementos finitos, o m?todo dos
momentos e o m?todo das diferen?as finitas no dom?nio do tempo. Entretanto, estes
m?todos apesar de precisos requerem um grande esfor?o computacional. Neste contexto,
a intelig?ncia computacional (IC) tem sido utilizada com sucesso nos projetos e na
otimiza??o de estruturas planares de microondas, como uma ferramenta auxiliar e muito
adequada, dada a complexidade das geometrias das antenas e das FSS consideradas. A
intelig?ncia computacional ? inspirada em fen?menos naturais como: aprendizado,
percep??o e decis?o, utilizando t?cnicas como redes neurais artificiais, l?gica fuzzy,
geometria fractal e computa??o evolucion?ria. Este trabalho realiza um estudo de
aplica??o de intelig?ncia computacional utilizando metaheur?sticas como algoritmos
gen?ticos e intelig?ncia de enxames na otimiza??o de antenas e superf?cies seletivas de
frequ?ncia. Os algoritmos gen?ticos s?o m?todos computacionais de busca baseados na
teoria da sele??o natural proposta por Darwin e na gen?tica utilizados para resolver
problemas complexos como, por exemplo, problemas em que o espa?o de busca cresce
com as dimens?es do problema. A otimiza??o por enxame de part?culas tem como
caracter?sticas a utiliza??o da intelig?ncia de forma coletiva sendo aplicada em
problemas de otimiza??o em diversas ?reas de pesquisa. O objetivo principal deste
trabalho consiste na utiliza??o da intelig?ncia computacional, na an?lise e s?ntese de
antenas e de FSS. Foram consideradas as estruturas de um monopolo planar de microfita,
do tipo anel, e de uma FSS de dipolos em cruz. Foram desenvolvidos os algoritmos de
otimiza??o e obtidos resultados para as geometrias otimizadas de antenas e FSS
consideradas. Para a valida??o de resultados foram projetados, constru?dos e medidos
v?rios prot?tipos. Os resultados medidos apresentaram excelente concord?ncia com os
simulados. Al?m disso, os resultados obtidos neste trabalho foram comparados com os
simulados atrav?s de um software comercial, tendo sido observada tamb?m uma
excelente concord?ncia. Especificamente, a efici?ncia das t?cnicas de IC utilizadas foram
comprovadas atrav?s de resultados simulados e medidos, objetivando a otimiza??o da
largura de banda de uma antena para opera??o em banda ultralarga, ou UWB (Ultra
Wideband), com a utiliza??o de um algoritmo gen?tico e da otimiza??o da largura de
banda, atrav?s da especifica??o do comprimento do gap de ar entre duas superf?cies
seletivas de frequ?ncia, utilizando um algoritmo de otimiza??o por enxame de part?culas
|
28 |
An?lise e projeto de superf?cies seletivas de frequ?ncia com elementos pr?-fractais para aplica??es em comunica??es indoorN?brega, Clarissa de Lucena 09 April 2013 (has links)
Made available in DSpace on 2014-12-17T14:55:11Z (GMT). No. of bitstreams: 1
ClarissaLN_TESE.pdf: 4153617 bytes, checksum: 6a9b7ed40b1f66da758afee4efaf74e9 (MD5)
Previous issue date: 2013-04-09 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this thesis, a frequency selective surface (FSS) consists of a two-dimensional
periodic structure mounted on a dielectric substrate, which is capable of selecting signals in
one or more frequency bands of interest. In search of better performance, more compact
dimensions, low cost manufacturing, among other characteristics, these periodic structures
have been continually optimized over time. Due to its spectral characteristics, which are
similar to band-stop or band-pass filters, the FSSs have been studied and used in several
applications for more than four decades. The design of an FSS with a periodic structure
composed by pre-fractal elements facilitates the tuning of these spatial filters and the
adjustment of its electromagnetic parameters, enabling a compact design which generally has
a stable frequency response and superior performance relative to its euclidean counterpart.
The unique properties of geometric fractals have shown to be useful, mainly in the production
of antennas and frequency selective surfaces, enabling innovative solutions and commercial
applications in microwave range. In recent applications, the FSSs modify the indoor
propagation environments (emerging concept called wireless building ). In this context, the
use of pre-fractal elements has also shown promising results, allowing a more effective
filtering of more than one frequency band with a single-layer structure. This thesis approaches
the design of FSSs using pre-fractal elements based on Vicsek, Peano and teragons
geometries, which act as band-stop spatial filters. The transmission properties of the periodic
surfaces are analyzed to design compact and efficient devices with stable frequency
responses, applicable to microwave frequency range and suitable for use in indoor
communications. The results are discussed in terms of the electromagnetic effect resulting
from the variation of parameters such as: fractal iteration number (or fractal level), scale
factor, fractal dimension and periodicity of FSS, according the pre-fractal element applied on
the surface. The analysis of the fractal dimension s influence on the resonant properties of a
FSS is a new contribution in relation to researches about microwave devices that use fractal
geometry. Due to its own characteristics and the geometric shape of the Peano pre-fractal
elements, the reconfiguration possibility of these structures is also investigated and discussed. This thesis also approaches, the construction of efficient selective filters with new
configurations of teragons pre-fractal patches, proposed to control the WLAN coverage in
indoor environments by rejecting the signals in the bands of 2.4~2.5 GHz (IEEE 802.11 b)
and 5.0~6.0 GHz (IEEE 802.11a). The FSSs are initially analyzed through simulations
performed by commercial software s: Ansoft DesignerTM and HFSSTM. The fractal design
methodology is validated by experimental characterization of the built prototypes, using
alternatively, different measurement setups, with commercial horn antennas and microstrip
monopoles fabricated for low cost measurements / Nesta tese, uma superf?cie seletiva de frequ?ncia (FSS) consiste de uma estrutura
peri?dica bidimensional montada sobre um substrato diel?trico, que ? capaz de selecionar
sinais em uma ou mais faixas de frequ?ncias de interesse. Em busca da obten??o de um
melhor desempenho, dimens?es mais compactas, baixo custo de fabrica??o, entre outras
caracter?sticas, estas estruturas peri?dicas t?m sido continuamente otimizadas ao longo do
tempo. Devido ?s suas caracter?sticas espectrais, que s?o similares as de filtros rejeita-faixa ou
passa-faixa, as FSSs t?m sido estudadas e usadas em aplica??es diversas por mais de quatro
d?cadas. O projeto de uma FSS com uma estrutura peri?dica composta de elementos pr?fractais
facilita a sintonia destes filtros espaciais e o ajuste de seus par?metros
eletromagn?ticos, possibilitando uma constru??o compacta, que, em geral, apresenta uma
resposta est?vel em frequ?ncia e desempenho superior em rela??o ? sua contrapartida
euclidiana. As propriedades ?nicas dos fractais geom?tricos t?m-se mostrado bastante ?teis,
principalmente para a constru??o de antenas e superf?cies seletivas de frequ?ncia, permitindo
solu??es inovadoras e aplica??es comerciais na faixa de micro-ondas. Em aplica??es mais
recentes, as FSSs modificam os ambientes de propaga??o indoor (conceito emergente
chamado de wireless building ). Neste contexto, o uso de elementos pr?-fractais tamb?m tem
apresentado resultados promissores, tornando mais efetiva a filtragem de mais de uma faixa
de frequ?ncias com uma estrutura de camada simples. Esta tese aborda o projeto de FSSs com
elementos pr?-fractais baseados nas geometrias de Vicsek, Peano e dos ter?gonos, que
funcionam como filtros espaciais do tipo rejeita-faixa. As propriedades de transmiss?o das
superf?cies peri?dicas s?o analisadas para a concep??o de dispositivos eficientes, compactos e
com respostas est?veis em frequ?ncia, aplic?veis na faixa de micro-ondas e adequados para
utiliza??es em comunica??es indoor. Os resultados s?o discutidos em termos do efeito
eletromagn?tico decorrente da varia??o de par?metros como, n?mero de itera??es fractais (ou
n?vel do fractal), fator de escala, dimens?o fractal e periodicidade da FSS, de acordo com o
elemento pr?-fractal utilizado. A an?lise da influ?ncia da dimens?o fractal sobre as
propriedades de resson?ncia de uma FSS ? uma contribui??o nova no que diz respeito ?s pesquisas com dispositivos de micro-ondas que utilizam geometrias fractais. Devido ?s
caracter?sticas pr?prias e a forma geom?trica dos elementos pr?-fractais de Peano, a
possibilidade de reconfigura??o destas estruturas tamb?m ? investigada e discutida. Esta tese
aborda ainda, a constru??o de filtros seletivos eficientes com novas configura??es de patches
pr?-fractais do tipo ter?gonos, propostos para controle de cobertura WLAN em ambientes
indoor, rejeitando os sinais nas faixas de 2,4~2,5 GHz (IEEE 802.11b) e 5,0~6,0 GHz (IEEE
802.11a). As FSSs s?o analisadas inicialmente por meio de simula??es executadas pelos
programas comerciais Ansoft DesignerTM e HFSSTM. A metodologia de projeto ? validada
atrav?s da caracteriza??o experimental dos prot?tipos constru?dos utilizando,
alternativamente, diferentes setups de medi??o, com antenas corneta comerciais e monopolos
de microfita de fabrica??o pr?pria para medi??es de baixo custo
|
29 |
Otimiza??o de superf?cies seletivas de frequ?ncia com elementos pr?-fractais utilizando rede neural MLP e algoritmos de busca populacionalSilva, Marcelo Ribeiro da 27 January 2014 (has links)
Made available in DSpace on 2014-12-17T14:55:18Z (GMT). No. of bitstreams: 1
MarceloRS_TESE.pdf: 2113878 bytes, checksum: 1cc62a66f14cc48f2e97f986a4dbbb8d (MD5)
Previous issue date: 2014-01-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This thesis describes design methodologies for frequency selective surfaces (FSSs)
composed of periodic arrays of pre-fractals metallic patches on single-layer dielectrics (FR4,
RT/duroid). Shapes presented by Sierpinski island and T fractal geometries are exploited to
the simple design of efficient band-stop spatial filters with applications in the range of
microwaves. Initial results are discussed in terms of the electromagnetic effect resulting from
the variation of parameters such as, fractal iteration number (or fractal level), fractal iteration
factor, and periodicity of FSS, depending on the used pre-fractal element (Sierpinski island or
T fractal). The transmission properties of these proposed periodic arrays are investigated
through simulations performed by Ansoft DesignerTM and Ansoft HFSSTM commercial
softwares that run full-wave methods. To validate the employed methodology, FSS prototypes
are selected for fabrication and measurement. The obtained results point to interesting features
for FSS spatial filters: compactness, with high values of frequency compression factor; as
well as stable frequency responses at oblique incidence of plane waves. This thesis also
approaches, as it main focus, the application of an alternative electromagnetic (EM)
optimization technique for analysis and synthesis of FSSs with fractal motifs. In application
examples of this technique, Vicsek and Sierpinski pre-fractal elements are used in the optimal
design of FSS structures. Based on computational intelligence tools, the proposed technique
overcomes the high computational cost associated to the full-wave parametric analyzes. To
this end, fast and accurate multilayer perceptron (MLP) neural network models are developed
using different parameters as design input variables. These neural network models aim to
calculate the cost function in the iterations of population-based search algorithms. Continuous
genetic algorithm (GA), particle swarm optimization (PSO), and bees algorithm (BA) are
used for FSSs optimization with specific resonant frequency and bandwidth. The performance
of these algorithms is compared in terms of computational cost and numerical convergence.
Consistent results can be verified by the excellent agreement obtained between simulations
and measurements related to FSS prototypes built with a given fractal iteration / Esta tese descreve metodologias de projeto para superf?cies seletivas de frequ?ncia
(FSSs) compostas por arranjos peri?dicos de patches met?licos pr?-fractais impressos em
camadas diel?tricas simples (FR4, RT/duroid). As formas apresentadas pelas geometrias
correspondentes ? ilha de Sierpinski e ao fractal T s?o exploradas para o projeto simples de
filtros espaciais rejeita-faixa eficientes com aplica??es na faixa de micro-ondas. Resultados
iniciais s?o discutidos em termos do efeito eletromagn?tico decorrente da varia??o de
par?metros como, n?mero de itera??es fractais (ou n?vel do fractal), fator de itera??o fractal, e
periodicidade da FSS, dependendo do elemento pr?-fractal utilizado (ilha de Sierpinski ou
fractal T). As propriedades de transmiss?o destes arranjos peri?dicos propostos s?o
investigadas atrav?s de simula??es realizadas pelos programas comerciais Ansoft DesignerTM
e Ansoft HFSSTM, que executam m?todos de onda completa. Para validar a metodologia
empregada, prot?tipos de FSS s?o selecionados para fabrica??o e medi??o. Os resultados
obtidos apontam caracter?sticas interessantes para filtros espaciais de FSS, tais como:
estrutura compacta, com maiores fatores de compress?o de frequ?ncia; al?m de respostas
est?veis em frequ?ncia com rela??o ? incid?ncia obl?qua de ondas planas. Esta tese aborda
ainda, como enfoque principal, a aplica??o de uma t?cnica alternativa de otimiza??o
eletromagn?tica (EM) para an?lise e s?ntese de FSSs com motivos fractais. Em exemplos de
aplica??o desta t?cnica, elementos pr?-fractais de Vicsek e Sierpinski s?o usados no projeto
?timo das estruturas de FSS. Baseada em ferramentas de intelig?ncia computacional, a t?cnica
proposta supera o alto custo computacional proveniente das an?lises param?tricas de onda
completa. Para este fim, s?o desenvolvidos modelos r?pidos e precisos de rede neural do tipo
perceptron de m?ltiplas camadas (MLP) utilizando diferentes par?metros como vari?veis de
entrada do projeto. Estes modelos de rede neural t?m como objetivo calcular a fun??o custo
nas itera??es dos algoritmos de busca populacional. O algoritmo gen?tico cont?nuo (GA), a
otimiza??o por enxame de part?culas (PSO), e o algoritmo das abelhas (BA), s?o usados para
a otimiza??o das FSSs com valores espec?ficos de frequ?ncia de resson?ncia e largura de
banda. O desempenho destes algoritmos ? comparado em termos do custo computacional e da
13
converg?ncia num?rica. Resultados consistentes podem ser verificados atrav?s da excelente
concord?ncia obtida entre simula??es e medi??es referentes aos prot?tipos de FSS constru?dos
com uma dada itera??o fractal
|
30 |
Aplica??o de superf?cies seletivas em frequ?ncia para melhoria de resposta de arranjos de antenas planaresAlmeida Filho, Valdez Arag?o de 12 March 2014 (has links)
Made available in DSpace on 2014-12-17T14:55:20Z (GMT). No. of bitstreams: 1
ValdezAAF_TESE.pdf: 2001050 bytes, checksum: d0f0b88178102c3f48880303c1c6d765 (MD5)
Previous issue date: 2014-03-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work aims to show how the application of frequency selective surfaces (FSS) in planar antenna arrays become an alternative to obtain desired radiation characteristics from changes in radiation parameters of the arrays, such as bandwidth, gain and directivity. In addition to analyzing these parameters is also made a study of the mutual coupling between the elements of the array. To accomplish this study, were designed a microstrip antenna array with two patch elements, fed by a network feed. Another change made in the array was the use of the truncated ground plane, with the objective of increasing the bandwidth and miniaturize the elements of the array. In order to study the behavior of frequency selective surfaces applied in antenna arrays, three different layouts were proposed. The first layout uses the FSS as a superstrate (above the array). The second layout uses the FSS as reflector element (below the array). The third layout is placed between two FSS. Numerical and experimental results for each of the proposed configurations are presented in order to validate the research / Este trabalho tem como objetivo apresentar como a aplica??o de superf?cies seletivas em frequ?ncia (FSS) em arranjos de antenas planares se torna uma alternativa interessante para se obter caracter?sticas de radia??o desejadas, a partir de altera??es em par?metros de radia??o dos arranjos, tais como largura de banda, ganho e diretividade. Al?m de analisar esses par?metros, tamb?m ? feito o estudo do acoplamento m?tuo entre os elementos do arranjo. Para realizar tal estudo, foi projetado um arranjo de antenas de microfita, com dois elementos do tipo patch, alimentado por uma rede de alimenta??o. Outra modifica??o feita no arranjo foi a utiliza??o do plano de terra truncado, com o objetivo de aumentar a largura de banda e miniaturizar os elementos do arranjo. Para poder estudar o comportamento das superf?cies seletivas em frequ?ncia aplicadas em arranjos de antenas, foram propostos tr?s layouts diferentes. O primeiro layout consiste em utilizar a FSS como superstrato (acima do arranjo). O segundo consiste em utilizar a FSS como elemento refletor (abaixo do arranjo). O terceiro layout consiste em colocar o arranjo entre duas camadas de FSS, tanto em cima quanto abaixo. Resultados num?ricos e experimentais para cada uma das configura??es propostas s?o apresentados
|
Page generated in 0.0619 seconds