Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Neste trabalho realizou-se estudos em escala laboratorial de soluÃÃes sÃlidas, procedentes dos precursores Fe2O3, BaCO3 e SrCO3, atravÃs do processo de moagem mecÃnica de alta energia, foram produzidos com sucesso pÃs nanocristalinos de BaxSr1-xFe12O19 (onde 0 x 1)os quais atravÃs de estudos de suas propriedades estruturais, morfolÃgicas e elÃtricas foram caracterizados. As propriedades das hexaferritas do tipo M de bÃrio ou de estrÃncio sÃo de grande interesse nas aplicaÃÃes de magnetos permanentes, meios de registros magnÃticos, dispositivos de microondas, absorvedores e sensores. Essas soluÃÃes sÃlidas substitucionais, depois de moÃdas receberam procedimento cerÃmico tradicional (procedimento do estado sÃlido). A estrutura cristalina das amostras foram identificadas por difraÃÃo de raios-X (hexagonal) pertencem ao grupo espacial P63/mmc. Os dados de difraÃÃo de raios-X foram refinados pelo mÃtodo Reitveld. Fez-se uso da espectroscopia MÃssbauer para realizar a sondagem do ferro presente na estrutura cristalina, constatando-se o estado de oxidaÃÃo do ferro (Fe3+) presente nos materiais analisados e a geometria do sÃtio cristalino no qual està presente. A morfologia e o tamanho mÃdio dos espÃcimes, na forma de pastilhas, foram analisados por Microscopia EletrÃnica de Varredura [216 â 339 nm], assistida por Energia Dispersiva de Raios-X, para analise quÃmica elementar. Foi realizado o estudo da constante dielÃtrica (Kâ), do fator de perda dielÃtrica (tg ) e a propriedade de condutividade elÃtrica () As propriedades dielÃtricas e elÃtrica foram analisadas em funÃÃo da freqÃÃncia, a temperatura ambiente, numa faixa compreendida entre 100 Hz e 40 MHz. Nos resultados das propriedades dielÃtricas, constatou-se que a amostra BFO100 apresenta a maior constante dielÃtrica (Kâ = 394,79) e a maior condutividade elÃtrica ( = 1,98 . 10-5 -1.m-1), porÃm, a menor perda dielÃtrica verificou-se nas amostras BFO75 e BFO90 (em ambas 0,81). Em virtude da constante dielÃtrica observada o espÃcime BFO100 apresenta o melhor perfil para aplicaÃÃes de RF (radio freqÃÃncia). / In this work he took place studies in laboratorial scale of solid solutions, coming from the precursors Fe 2 O 3 , BaCO 3 and SrCO 3 , through the process of mechanical high-energy ball milling, were produced with success powders nanocrystalline o f Ba x Sr 1-x Fe 12 O 19 (where 0 ≤ x ≤ 1)os which were characterized through studies of their properties structural, morphologic and electric. The properties of the hexaferritas of the type barium M or of strontium they are of great interest in the applications of permanent magnetos, means of magnetic registrations, devices of microwaves, absorbers and sensor. Those solid substitucionais solutions, after prepared milled received traditional ceramic procedure (procedure of the solid state). The crystalline structure of the specimens was identified by diffraction of ray-X (hexagonal) they belong to the space group P63/mmc. The diffraction data of ray-X were refined for the method Reitveld. Use of the spectroscopy was made MÃssbauer to accomplish the survey of the present iron in the crystalline structure, being verified the state of oxidation of the iron (Fe3+) present in the analyzed materials and the geometry of the crystalline ranch in which it present. The morphology and the medium size of the specimens, in the form of tablets, they were observed by Scanning Electron Microscopy (SEM) [216-339 nm], attended by Energy Dispersive Ray-X (EDX), for it analyzes elementary chemistry. The study of the dielectric constant was accomplished (K'), of the factor of loss dielectric (tg δ) and the property of electric conductivity ( σ). The properties dielectrics and electric they were analyzed in function of the frequency, to room temperature, in a strip understood between 100 Hz and 40 MHz. In the re sults of the properties dielectrics, it was verified that the sample BFO100 shows the largest result of the dielectric constant (K ' = 394,79) and the largest electric conductivity (σ = 1,98. 10 -5 Ω -1 .m -1 ), however, to smallest loss dielectric it was verified in the samples BFO75 and BFO90 (in both 0,81). In virtue of the constant dielectric observed, the specimen BFO100 shows the best profile for applications of RF (I radiate frequency).

Les composants passifs hyperfréquences deviennent de plus en plus commercialisés et employés dans les systèmes de télécommunications. La croissance technologique et l’augmentation de la demande des nouvelles applications requièrent de meilleures performances et de moindres coûts. Dans les applications sans fil et notamment dans les modules « émission/réception », les circulateurs sont utilisés pour l’émission et la réception des signaux simultanément à l’aide d’une seule antenne. Les couches magnétiques traditionnellement déposées et intégrées exigent une cristallisation à haute température ainsi que l’application d’un champ magnétique externe pour garder l’orientation des moments magnétiques. Cette orientation est cependant obtenue par des aimants lourds et volumineux. Devant ces limitations technologiques ainsi que la demande de miniaturisation, l’emploi de l’hexaferrite de baryum sous sa forme particulaire devrait permettre le développement de circulateurs auto-polarisés et miniaturisés à matériaux magnétiques composites. Les travaux présentés dans ce manuscrit ont pour objectif d’étudier et de réaliser un circulateur hyperfréquence à nano particules magnétiques orientées dans la bande 40-60 GHz. L’état de l’art expose les différentes topologies de circulateurs dont la topologie coplanaire est choisie pour notre application. L’étude analytique est basée sur les travaux de Bosma permettant de modéliser le circulateur triplaque. Les principales dimensions géométriques obtenues sont ensuite transposées vers la structure coplanaire en 3D à l’aide de l’outil de simulation HFSS. Devant les limitations de cet outil, différentes structures ont été étudiées et simulées numériquement pour présenter au mieux le matériau composite. Plusieurs séries de prototypes sont ensuite fabriquées à partir des structures optimisées en simulation numérique. Le matériau magnétique composite déposé a des épaisseurs de 40 et 100 μm. Les caractérisations hyperfréquences montrent la performance des dispositifs réalisés. Des pistes de recherche sont proposées pour l’amélioration des performances de nos prototypes / Microwave passive components become increasingly commercialized and used in telecommunications systems. Technological growth and the increased demand for new applications require higher performance and lower costs. In wireless applications, especially in "transceivers", circulators are used for transmitting and receiving signals simultaneously using a single antenna. Magnetic layers traditionally deposited and integrated require a high crystallization temperature and the application of an external magnetic field to keep the orientation of magnetic moments. This orientation is however obtained by heavy and bulky magnets. Given these technological limitations and the need to miniaturize, the use of barium hexaferrite particles envisages the development of self-biased and miniaturized circulators having magnetic composite materials. The ambition of this work is to study and to fabricate a microwave circulator with magnetic nanoparticles oriented in the 40 - 60 GHz range. The state of the art describes various topologies coplanar circulators from which the coplanar topology is chosen for our application. The analytical study is based on Bosma’s work to model the stripline circulator. The main geometric dimensions obtained are then transposed to the coplanar structure using the 3D simulation tool HFSS. Faced with this tool’s limitations, different structures were studied and simulated numerically to shape the best the composite material. Several series of prototypes are then manufactured. The magnetic composite material was deposited in layers having thicknesses of 40 and 100 μm. The microwave characterizations show the performance of the fabricated device. Research tracks are proposed to improve the performance of our prototypes

Ce mémoire porte sur la synthèse et la caractérisation de composés hexaferrites dans le système Ca-Fe-O. Ce travail a permis d’isoler quatre composés sous forme polycristalline ayant pour composition (Ca4Fe5O13)1-x(Fe9O12)1+x (x= 0,334 ; 0,301 et 0,128) et (Ca4Fe5O13)(Fe4O4). Leur structure cristalline a été déterminée à partir de données de diffraction électronique acquises en mode tomographie par précession des électrons et validée à l’aide de l’imagerie haute résolution (HREM et HAADF). Les différents modèles structuraux ont également été confirmés par diffraction des rayons X et des neutrons sur poudre. L’analyse fine des défauts d’intercroissance en imagerie HAADF a révélée des écarts significatifs de composition par rapport à la composition idéale (Ca4Fe5O13)(Fe9O12) à l’origine des trois polymorphes observés. En complément des études menées sur des cristaux de taille micrométrique dans les années 80, l’obtention d’échantillons polycristallins a rendu possible l’étude des propriétés physiques de ces composés. Malgré la complexité de ces structures et la présence de défauts étendus, la spectrométrie Mössbauer a mis en exergue un degré d’oxydation unique pour les atomes de fer (+3) et de confirmer les nombreuses transitions magnétiques initialement détectées par les mesures d’aimantation, ainsi que leur évolution en fonction de l’écart à la stœchiométrie x. Les composés ont également été caractérisés par des mesures de résistivité électrique et de coefficient Seebeck. / This thesis reports on the synthesis and the characterization of hexaferrite compounds in the Ca-Fe-O system. This work has allowed to isolate four polycrystalline compounds presenting the chemical formula (Ca4Fe5O13)1-x(Fe9O12)1+x (x= 0.334; 0.301 and 0.128) and (Ca4Fe5O13)(Fe4O4). Their crystalline structure has been determined using the precession electron diffraction tomography and has been validated through high resolution imaging microscopy (HREM/HAADF). X-ray diffraction and neutron diffraction studies on polycrystalline samples have confirmed the different structural models. Fine analysis of intergrowth defects in HAADF imaging revealed significant deviations in composition with respect to the ideal composition (Ca4Fe5O13)(Fe9O12) at the origin of the three observed polymorphs. In addition to the studies on micron-sized crystals in the 80s, obtaining polycrystralline samples allowed the measurement of their physical properties. Despite the complexity of these structures and the presence of extensive defects, the Mössbauer spectroscopy has highlighted a unique oxidation degree of iron (+3) and confirmed as well the various magnetic transitions initially detected by magnetization measurements, as well as their evolution versus the x deviation value. Electrical resistivity and Seebeck coefficient measurements were performed on the samples.

Communication and reconnaissance systems are requiring increasing flexibility concerning functionality and efficiency for multiband and broadband frequency applications. Circuit-based reconfiguration mechanisms continue to promote radio frequency (RF) application flexibility; however, increasing limitations have resulted in hindering performance. Therefore, the implementation of a "wireless" reconfiguration mechanism provides the required agility and amicability for microwave circuits and antennas without local overhead. The wireless reconfiguration mechanism in this thesis integrates dynamic, fluidic-based material systems to achieve electromagnetic agility and reduce the need for "wired" reconfiguration technologies. The dynamic material system component has become known as electromagnetically functionalized colloidal dispersions (EFCDs). In a microfluidic reconfiguration system, they provide electromagnetic agility by altering the colloidal volume fraction of EFCDs - their name highlights the special considerations we give to material systems in applied electromagnetics towards lowering loss and reducing system complexity. Utilizing EFCDs at the RF device-level produced the first circuit-type integration of this reconfiguration system; this is identified as the coaxial stub microfluidic impedance transformer (COSMIX). The COSMIX is a small hollowed segment of transmission line with results showing a full reactive loop (capacitive to inductive tuning) around the Smith chart over a 1.2 GHz bandwidth. A second microfluidic application demonstrates a novel antenna reconfiguration mechanism for a 3 GHz microstrip patch antenna. Results showed a 300 MHz downward frequency shift by dielectric colloidal dispersions. Magnetic material produced a 40 MHz frequency shift. The final application demonstrates the dynamically altering microfluidic system for a 3 GHz 1x2 array of linearly polarized microstrip patch antennas. The parallel microfluidic capillaries were imbedded in polydimethylsiloxane (PDMS). Both E- and H-plane designs showed a 250 MHz frequency shift by dielectric colloidal dispersions. Results showed a strong correlation between decreasing electrical length of the elements and an increase of the volume fraction, causing frequency to decrease and mutual coupling to increase. Measured, modeled, and analytical results for impedance, voltage standing wave ratio (VSWR), and radiation behavior (where applicable) are provided.

Communication and reconnaissance systems are requiring increasing flexibility concerning functionality and efficiency for multiband and broadband frequency applications. Circuit-based reconfiguration mechanisms continue to promote radio frequency (RF) application flexibility; however, increasing limitations have resulted in hindering performance. Therefore, the implementation of a "wireless" reconfiguration mechanism provides the required agility and amicability for microwave circuits and antennas without local overhead. The wireless reconfiguration mechanism in this thesis integrates dynamic, fluidic-based material systems to achieve electromagnetic agility and reduce the need for "wired" reconfiguration technologies. The dynamic material system component has become known as electromagnetically functionalized colloidal dispersions (EFCDs). In a microfluidic reconfiguration system, they provide electromagnetic agility by altering the colloidal volume fraction of EFCDs - their name highlights the special considerations we give to material systems in applied electromagnetics towards lowering loss and reducing system complexity. Utilizing EFCDs at the RF device-level produced the first circuit-type integration of this reconfiguration system; this is identified as the coaxial stub microfluidic impedance transformer (COSMIX). The COSMIX is a small hollowed segment of transmission line with results showing a full reactive loop (capacitive to inductive tuning) around the Smith chart over a 1.2 GHz bandwidth. A second microfluidic application demonstrates a novel antenna reconfiguration mechanism for a 3 GHz microstrip patch antenna. Results showed a 300 MHz downward frequency shift by dielectric colloidal dispersions. Magnetic material produced a 40 MHz frequency shift. The final application demonstrates the dynamically altering microfluidic system for a 3 GHz 1x2 array of linearly polarized microstrip patch antennas. The parallel microfluidic capillaries were imbedded in polydimethylsiloxane (PDMS). Both E- and H-plane designs showed a 250 MHz frequency shift by dielectric colloidal dispersions. Results showed a strong correlation between decreasing electrical length of the elements and an increase of the volume fraction, causing frequency to decrease and mutual coupling to increase. Measured, modeled, and analytical results for impedance, voltage standing wave ratio (VSWR), and radiation behavior (where applicable) are provided.