"March, 2009". / Thesis (PhD)--Macquarie University, Faculty of Science, Dept. of Physics & Engineering, 2008. / Bibliography: p. 145-158. / Introduction -- Frequency selective surfaces -- Absorb/transmit frequency selective surface absorber -- Switchable frequency selective surface for wireless applications -- Energy-saving glass characterisation -- Frequency selective surface solution for energy-saving glass -- Conclusion. / This thesis presents three topics related to frequency selective surfaces (FSSs), namely bsorb/transmit FSSs, active FSSs and passive bandpass FSSs for energy-saving glass used in modern buildings. These three FSSs are unique in their design and functionalities. The absorb/transmit FSS is a novel dual-layer frequency selective surface for 5 GHz WLAN applications. This FSS can stop propagation of specific bands by absorbing as opposed to re ecting, while passing other useful signals. This is in contrast to the conventional Salisbury and Jaumann absorbers, which provide good absorption in the desired band while the out-of-band frequencies are attenuated. The second topic is a single-layer bandpass active FSS that can be switched between ON and OFF states to control the transmission in 2.45 GHz WLAN applications. Previously, researchers have focused on the bandstop and dual-layer versions of the active FSS. This is in contrast to the design presented in this thesis which is single-layer and provides extra advantage in a practical WLAN environment. Also the dc biasing techniques that were used for the active FSS design are easier to implement and provide good frequency stability for different angles of incidence and polarisations in both ON and OFF states. The last topic is on the use of a bandpass FSS in energy-saving glass panels used in building design. The manufacturers of these glass panels apply a very thin metal-oxide coating on one side of the glass panels to provide extra infrared (heat) attenuation. However, due to the presence of the coating, these energy-saving glass panels also attenuate communication signals such as GSM 900, GSM 1800/1900, UMTS and 3G mobile signals etc. This creates a major communication problem when buildings are constructed with windows of this glass. In this thesis, a solution to this problem is presented by designing and etching a cross-dipole bandpass FSS on the coated side of the glass to pass the useful signals while keeping infrared attenuation at an acceptable level. One of the advantages of this FSS design is that measured material values of the metal-oxide coating are used for simulations, which have not been done previously. / Mode of access: World Wide Web. / 166 p. ill. (some col.)

Les surfaces sélectives en fréquence (FSS) pour la furtivité radar ou l’optique ont été largement étudiées. Depuis plus de vingt ans, des matériaux artificiels ont été conçus, permettant d’obtenir des propriétés particulières, notamment l’existence de bandes permises ou interdites, réfraction négative, ultra-réfraction. Par ailleurs, des antennes basées sur la mise en réseau d’un élément rayonnant sont plus compactes et plus facilement intégrables. Le problème de la diffraction d’une onde plane par des réseaux tridimensionnels bipériodiques peut être résolu par éléments finis ou par équations intégrales bipériodiques ; il l’est souvent par une méthode hybride combinant la méthode des éléments finis et la méthode aux équations intégrales. Nous avons choisi de développer une méthode hybride utilisant deux variantes de la méthode aux équations intégrales. Les domaines semi-infinis (l’extérieur du réseau) sont traités par des équations intégrales bipériodiques (EI3D2D), et les domaines bornés (l’intérieur du réseau) sont traités par des équations intégrales tridimensionnelles (EI3D), auxquelles on impose des conditions aux limites de pseudopériodicité. Ce code numérique est développé dans le cadre du code SPECTRE de Dassault-Aviation, qui est un code généraliste 3D, afin de bénéficier de la richesse des modèles qui y ont déjà été développés (modèle composé d’un nombre quelconque de sous-domaines de formes et de matériaux quelconques, traitement des différents cas de jonctions entre sous-domaines, matériaux de faible épaisseur). L’efficacité en termes de précision et en temps de calcul de la méthode numérique est validée par comparaison des résultats avec d’autres simulations numériques et également avec des résultats de mesures. Les cas testés sont représentatifs de plusieurs des principaux phénomènes liés aux métamatériaux : surfaces sélectives en fréquence, transmission « extraordinaire », surfaces à haute impédance. Enfin, nous étudions un radôme passe-bande indépendant à l’angle d’incidence, à l’aide de la méthode numérique que nous proposons. La structure retenue se base sur un réseau de cavités coaxiales dans une couche métallique. Nous expliquons l’origine physique des résonances qui apparaissent et nous suggérons une évolution géométrique du profil des cavités, afin d’augmenter la largeur de bande passante. / Frequency selective surfaces (FSS) for radar stealth or in optics have been widely studied. For more than two decades, articial materials have been designed to highlight specific behaviour, like the existence of allowed or forbidden bands, negative refraction, ultra-refraction... Moreover, antennas based upon an array of radiating elements improve the compactness and integration of these features. The problem of the diffraction of a plane wave by 3D biperiodic scatterers can be solved by finite-elements methods (FEM) or biperiodic boundary integral equations (BIE). It is often done by hybrid methods, that combine FEM and BIE. We choose to develop a hybrid method that uses two variants of the BIE method. Semiinfinite outer domains are treated by biperiodic integral equations (3D2D IE) and inner bounded domains are treated by 3D free-space integral equations (3D IE). Pseudoperiodic boundary conditions are enforced in the scattering biperiodic structure. The numerical code is developed in the framework of Dassault Aviation’s SPECTRE code, which is a general 3D code, in order to take advantage of the various models that have already been developed : arbitrary number of sub-domains of various shapes or materials, treatment of the different types of junctions between sub-domains, thin slabs. The efficiency in terms of accuracy and computation time of the numerical code is validated by comparison of the results from other numerical simulations or measurements. All the test cases are representative of several of the main phenomena that can be observed in metamaterials : FSS, “extraordinary” transmission, high-impedance surfaces. Finally, a bandpass radome which is independent to the angle of incidence is studied. The proposed numerical method is used. The chosen structure is based upon an array of coaxial cavities in a metallic slab. We explain the physical origin of resonances that appear and we suggest a geometrical evolution of the profile of the cavities, to favor a wideband behavior.

Thesis (PhD)--Macquarie University, Faculty of Science, Dept. of Physics & Engineering, 2008. / "March, 2009". Bibliography: p. 145-158.

Made available in DSpace on 2014-12-17T14:55:39Z (GMT). No. of bitstreams: 1 LincolnMA.pdf: 1667449 bytes, checksum: b8113389f31903ba22cf94dbc22192c1 (MD5) Previous issue date: 2009-08-13 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / This work presents a theoretical and numerical analysis of structures using frequency selective surfaces applied on patch antennas. The FDTD method is used to determine the time domain reflected fields. Applications of frequency selective surfaces and patch antennas cover a wide area of telecommunications, especially mobile communications, filters and WB antennas. scattering parameters are obteained from Fourier Transformer of transmited and reflected fields in time domain. The PML are used as absorbing boundary condition, allowing the determination of the fields with a small interference of reflections from discretized limit space. Rectangular patches are considered on dielectric layer and fed by microstrip line. Frequency selective surfaces with periodic and quasi-periodic structures are analyzed on both sides of antenna. A literature review of the use of frequency selective surfaces in patch antennas are also performed. Numerical results are also compared with measured results for return loss of analyzed structures. It is also presented suggestions of continuity to this work / Este trabalho apresenta uma an?lise te?rica e num?rica de estruturas que utilizam superf?cies seletivas de frequ?ncia aplicadas a antenas do tipo patch. Para isso, ? utilizado o m?todo das diferen?as finitas no dom?nio do tempo (FDTD) visando determinar os campos refletidos a partir de uma onda plana incidente no dom?nio do tempo. As aplica??es das superf?cies seletivas de freq??ncia e antenas patch abrangem uma grande ?rea das Telecomunica??es, principalmente em comunica??es m?veis e v?o desde filtros at? as antenas banda larga. Especificamente, a an?lise usa os campos transmitidos e refletidos obtidos no dom?nio do tempo, em conjunto com transformada de Fourier permitindo a obten??o dos par?metros de transmiss?o da antena. A condi??o de contorno absorvedora utilizada foi a de camada perfeitamente casada (PML), permitindo a determina??o num?rica dos campos com uma quantidade menor de interfer?ncias provenientes de reflex?es nos limites do espa?o discretizado. S?o considerados patches retangulares condutores sobre uma camada diel?trica e alimentados por linha de microfita. Foram analisadas superf?cies seletivas de frequ?ncia peri?dicas e quase peri?dicas tanto no plano de terra quanto no plano do pr?prio patch. ? realizada uma revis?o bibliogr?fica a respeito da utiliza??o de superf?cies seletivas de frequ?ncia em antenas patch. Tamb?m s?o comparados resultados num?ricos e medidos para a perda de retorno das estruturas analisadas. S?o apresentadas, ainda, sugest?es de continuidade para este trabalho

Made available in DSpace on 2014-12-17T14:56:06Z (GMT). No. of bitstreams: 1 JoseIAT_DISSERT.pdf: 2877383 bytes, checksum: 0665f7dd94ce1dd4d8883a4f2e5e7832 (MD5) Previous issue date: 2010-12-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work aims to investigate the behavior of fractal elements in planar microstrip structures. In particular, microstrip antennas and frequency selective surfaces (FSSs) had changed its conventional elements to fractal shapes. For microstrip antennas, was used as the radiating element of Minkowski fractal. The feeding method used was microstrip line. Some prototypes were built and the analysis revealed the possibility of miniaturization of structures, besides the multiband behavior, provided by the fractal element. In particular, the Minkowski fractal antenna level 3 was used to exploit the multiband feature, enabling simultaneous operation of two commercial tracks (Wi-Fi and WiMAX) regulated by ANATEL. After, we investigated the effect of switches that have been placed on the at the pre-fractal edges of radiating element. For the FSSs, the fractal used to elements of FSSs was D?rer s pentagon. Some prototypes were built and measured. The results showed a multiband behavior of the structure provided by fractal geometry. Then, a parametric analysis allowed the analysis of the variation of periodicity on the electromagnetic behavior of FSS, and its bandwidth and quality factor. For numerical and experimental characterization of the structures discussed was used, respectively, the commercial software Ansoft DesignerTM and a vector network analyzer, Agilent N5230A model / Este trabalho tem como objetivo investigar o comportamento de elementos fractais em estruturas planares de microfita. Em particular, as antenas de microfita e as superf?cies seletivas de frequ?ncia (FSSs) tiveram seus elementos convencionais alterados para formatos fractais. Para as antenas de microfita, usou-se como elemento radiante o fractal de Minkowski. O m?todo de alimenta??o utilizado nas antenas foi atrav?s de linha de microfita. Alguns prot?tipos foram constru?dos e a an?lise realizada mostrou a possibilidade de miniaturiza??o das estruturas, al?m do comportamento multibanda, proporcionado pelo elemento fractal. Em particular, a antena fractal de Minkowski de n?vel 3 foi utilizada para explorar a caracter?stica multibanda, possibilitando seu funcionamento simult?neo em duas faixas comerciais (Wi-Fi e WiMAX) regulamentadas pela ANATEL. Em seguida, foi investigado o efeito de chaves que foram colocadas nas bordas pr?-fractais do elemento radiante. Para as FSSs, o fractal adotado para atuar como elemento da FSS foi o pent?gono de D?rer. Alguns prot?tipos foram constru?dos e medidos. Os resultados mostraram um comportamento multibanda proporcionado pela geometria fractal. Em seguida, uma an?lise param?trica possibilitou a an?lise da influ?ncia da varia??o da periodicidade no comportamento eletromagn?tico das FSSs, bem como sua largura de banda e seu fator de qualidade. Na caracteriza??o num?rica e experimental das estruturas abordadas, utilizou-se, respectivamente, o software comercial Ansoft DesignerTM e um analisador de redes vetorial, modelo N5230A da Agilent

The manipulation of electromagnetic radiation via the use of periodic arrays of sub-wavelength metallic structures (unit cells), nowadays named "metamaterials", has been known of in the microwave engineering community for over fifty years. In the last decade interest in such sub-wavelength structures grew, mainly due to their ability to interact with radiation in ways natural materials could not e.g. by producing a negative refractive index (NRI). This project sought to see whether NRI metamaterials could provide benefits to the mm and sub-mm wavelength astronomical instrumentation currently in use. To aid rapid design and optimisation of devices made from a cascaded set of metamaterial unit cells, a hybridised Transmission Line (TL) model was developed where the matrix components used in the TL model were "seeded" with data taken from a Finite Element Method (FEM) model of a simpler structure. A comparison between the two found that the TL model was capable of providing results that differed from the FEM model by no more than ~10E−4 for the transmitted intensity, |S21|^2, and <1° for transmitted phase, arg(S21). A slab of material with a refractive index, n = −1, can exhibit an effect known as "superlensing". A three unit cell thick NRI slab was designed, manufactured and experimentally tested. It was found to be capable of producing an NRI across a fractional band of at least 21%, producing a refractive index value of n = −1 at around 90 GHz. The experimental and simulated transmission and reflection data show good match with each other. A highly birefringent air gap Half Wave Plate (HWP) was designed, manufactured and experimentally tested. Defining its useful bandwidth as the region where the phase difference, is equal to (−180 ± 3)° a single HWP had a fractional bandwidth of 0.3%. The bandwidth was extended by using the Pancharatnam method, developed in the 1950's to produce highly achromatic optical wave plates. The method however is applicable to other frequencies and polarisation control technologies. Optimising a three HWP TL-based Pancharatnam model, the HWP's modelled fractional bandwidth increased to 6.6%. Experimental data agrees with the model showing a plateauing of the phase difference at −180°. A highly birefringent polypropylene embedded Quarter Wave Plate (QWP) was also designed, manufactured and tested. Defining its useful bandwidth as the region where the differential phase is (90 ± 2)° a single QWP produced a fractional bandwidth of 0.6%. By optimising a four QWP TL-based Pancharatnam model, the QWP's performance was improved to 7.8%. Experimental data, whilst not in complete agreement with the model does show a reduction in the gradient of phase difference where it crossed 90°. It was found that current designs for NRI metamaterials fall short of the standards required to be used in quasi-optical astronomical instrumentation due to high dispersion and absorption. The high dispersion limits NRI metamaterials to uses in instruments built for narrowband applications. Whilst the Pancharatnam method can increase bandwidths where a flat differential phase response is required, this comes at the cost of increased absorption. To reach their full potential, NRI metamaterials' lossiness must be reduced e.g. possibly by cryogenic means or the use of "active" metamaterials.

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.

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.

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

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.