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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
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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
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/15242 |
| Date | 27 January 2014 |
| Creators | Silva, Marcelo Ribeiro da |
| Contributors | CPF:04401565487, Mendon?a, La?rcio Martins de, CPF:09064087415, http://lattes.cnpq.br/1853488415531363, Lins, Hertz Wilton de Castro, CPF:75112302453, http://lattes.cnpq.br/7712686175574736, Oliveira, Jos? de Ribamar Silva, CPF:12559520320, http://lattes.cnpq.br/4002176927695547, Melo, Marcos Tavares de, CPF:23162767415, http://lattes.cnpq.br/4933635747860906, D'assun??o, Adaildo Gomes |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Engenharia El?trica, UFRN, BR, Automa??o e Sistemas; Engenharia de Computa??o; Telecomunica??es |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | Portuguese |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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