Made available in DSpace on 2014-12-17T14:55:47Z (GMT). No. of bitstreams: 1 EmanueleSRM_DISSERT.pdf: 2423953 bytes, checksum: 516a98f7f1136b2e57265165c2a43b20 (MD5) Previous issue date: 2010-12-21 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Frequency Selective Surfaces (FSS) are periodic structures in one or two dimensions that act as spatial filters, can be formed by elements of type conductors patches or apertures, functioning as filters band-stop or band-pass respectively. The interest in the study of FSS has grown through the years, because such structures meet specific requirements as low-cost, reduced dimensions and weighs, beyond the possibility to integrate with other microwave circuits. The most varied applications for such structures have been investigated, as for example, radomes, antennas systems for airplanes, electromagnetic filters for reflective antennas, absorbers structures, etc. Several methods have been used for the analysis of FSS, among them, the Wave Method (WCIP). Are various shapes of elements that can be used in FSS, as for example, fractal type, which presents a relative geometric complexity. This work has as main objective to propose a simplification geometric procedure a fractal FSS, from the analysis of influence of details (gaps) of geometry of the same in behavior of the resonance frequency. Complementarily is shown a simple method to adjust the frequency resonance through analysis of a FSS, which uses a square basic cell, in which are inserted two reentrance and dimensions these reentrance are varied, making it possible to adjust the frequency. For this, the structures are analyzed numerically, using WCIP, and later are characterized experimentally comparing the results obtained. For the two cases is evaluated, the influence of electric and magnetic fields, the latter through the electric current density vector. Is realized a bibliographic study about the theme and are presented suggestions for the continuation of this work / As Superf?cies Seletivas de Frequ?ncia (FSS) s?o estruturas peri?dicas em uma ou duas dimens?es que atuam como filtros espaciais, podendo ser formadas por elementos do tipo patches condutores ou aberturas, funcionando como filtros rejeita-faixa ou passa-faixa, respectivamente. O interesse no estudo das FSS tem crescido atrav?s dos anos, pois tais estruturas atendem a requisitos espec?ficos como baixo custo, dimens?es e pesos reduzidos, al?m da possibilidade de se integrar com outros circuitos de micro-ondas. As mais variadas aplica??es para tais estruturas t?m sido investigadas, como por exemplo, radomes, sistemas de antenas para avi?es, filtros eletromagn?ticos para antenas refletoras, estruturas absorvedoras, etc. V?rios m?todos t?m sido utilizados para a an?lise de FSS, dentre eles, o M?todo das Ondas (WCIP). S?o diversas as formas de elementos que podem ser utilizados em FSS, como por exemplo, os do tipo fractal, que apresenta uma relativa complexidade geom?trica. Este trabalho tem como objetivo principal propor um procedimento de simplifica??o geom?trica de uma FSS fractal, a partir da an?lise da influ?ncia dos detalhes (fendas) da geometria da mesma no comportamento da frequ?ncia de resson?ncia. De forma complementar ? mostrado um m?todo simples de ajustar a frequ?ncia de resson?ncia atrav?s da an?lise de uma FSS, que utiliza uma c?lula b?sica retangular, na qual s?o inseridas duas reentr?ncias e as dimens?es dessas reentr?ncias s?o variadas, tornando poss?vel o ajuste da frequ?ncia. Para isso, as estruturas s?o analisadas numericamente, utilizando o WCIP, e posteriormente s?o caracterizadas experimentalmente, comparando-se os resultados obtidos. Para os dois casos ? avaliada, a influ?ncia dos campos el?trico e magn?tico, este ?ltimo atrav?s do vetor densidade de corrente el?trica. ? realizado um estudo bibliogr?fico a cerca do tema e s?o apresentadas sugest?es para a continuidade deste trabalho

O presente estudo teve por objetivo avaliar por meio da análise de freqüência de ressonância (AFR) o efeito da irradiação com laser de GaAlAs na estabilidade de implantes de titânio, como cociente de estabilidade do implante (ISQ) instalados em pacientes parcialmente edentados na região posterior da mandíbula; assim como avaliar a evolução da estabilidade dos implantes, durante o período de osseointegração. Foram selecionados 8 pacientes adultos, com boa saúde para a instalação cirúrgica de 30 implantes Xive S® (Dentsply). Portanto, foram instalados de 2 a 5 implantes por paciente, distribuídos bilateralmente. Cada paciente atuou como seu próprio controle. Os implantes do lado controle não foram irradiados, e os do lado experimental foram submetidos a terapia com laser de diodo GaAlAs com ?= 830 nm, densidade de energia de 8 j/cm2, potência de 100 mW, modo contínuo, de forma pontual em 20 pontos, durante 3 segundos por ponto. A primeira sessão de irradiação foi no pós-operatório imediato, sendo repetida a cada 48 horas nos primeiros 14 dias, totalizando 7 irradiações. Após a instalação dos implantes foi medida a estabilidade primária destes com o aparelho Osstell?. Novas medidas de ISQ foram realizadas após 10 dias, e 3, 6, 9 e 12 semanas. No momento da instalação, os valores de ISQ na região posterior da mandíbula oscilaram de 65-84 com média de 76, sofrendo queda significativa da estabilidade do 100 dia para a 6a semana no grupo irradiado e apresentando um aumento gradual a partir da 6a semana até a 12a semana. Os valores mais altos de ISQ foram observados no 100 dia no grupo irradiado, embora sem significância estatística, e os mais baixos foram observados na 6a semana em ambos os grupos. Não foi evidenciado o efeito do laser de GaAlAs na estabilidade dos implantes com o aparelho OsstellTM, porém não se pode afirmar que os padrões de reparação óssea e a taxa de osseointegração entre os implantes irradiados e não irradiados tenham sido similares. / JThe present study was carried out to evaluate the effect of irradiation with the GaALAs laser in the stability of titanium implants (ISQ), inserted in partially edentulous patients, by means of resonance frequency analysis (RFA); as well as to evaluate the evolution of the stability during the osseointegration processs. A group of 8 patients were seleted for the insertion of 30 implants (Xive S® - Dentsply). The implants in the control site were not irradiated, and the implants in the experimentall site were submitted to laser therapy with a GaAlAs with ?= 830 nm, energy density of 8 j/cm2, power of 100 mW, continuing mode, in 20 points, for 3 seconds per point. The first irradiation was immediately after the surgery, and it was repeated every 48 hours in the first 14 days, totalizing 7 irradiations. After the implants insertion, the primary stability was measured using Osstell?. New measurements were carried out after 10 days, 3, 6, 9, 12 weeks. The incial ISQ values ranged from 65-84, with a mean of 76, showing a significative decrease in the stability from the 10th day to the 6th weeks in the irradiated group, and showing a gradual increase from 6th to 12th week. The highest ISQ values were observed in the 10th day in the irradiated group, and the lower ISQ values were observed in the 6th week in both groups. The effect of the irradiation with GaAlAs laser in implant stability was not evicenced; however, it can not be affirmed that irradiated and not irradiated implants have similar bone repair patterns and osseointegration rates.

Cette thèse avait pour objectif d'augmenter la fréquence de travail d'un multicouche magnéto-diélectrique pour des applications des Nouvelles Technologies de l'Information et de la Communication (NTIC). Ainsi, deux types de structures ont été étudiés : des multicouches (CoO=CoFeB)n et des tricouches Py/Ru/Py. Dans les empilements (CoO=CoFeB)n, la montée en fréquence est assurée par une anisotropie de surface du CoFeB induite par une rugosité orientée à la surface de la couche CoO. Cette rugosité est générée par la géométrie de dépôt. La fréquence de résonance de ce système est ajustable sur toute la gamme de fréquence des NTIC par le choix des épaisseurs de CoO et de CoFeB. Ces propriétés magnétiques sont modélisées en ajoutant à l'anisotropie intrinsèque du CoFeB un terme démagnétisant. Celui-ci est calculé à partir des observations de la surface de la couche CoO par microscopie à force atomique. Les propriétés magnétiques obtenues sur le bicouche sont maintenues dans le cas d'un multicouche, montrant que la rugosité est peu affectée par l'empilement. Dans les tricouches Py/Ru/Py, le terme s'ajoutant à l'anisotropie intrinsèque du Py est induit par le couplage des deux couches de Py via les électrons de conduction de la couche de Ru (couplage RKKY). Selon les échantillons, le terme de couplage antiferromagnétique ou quadratique est prépondérant. La modélisation du comportement statique permet de quantifier ces termes de couplage. La modélisation du comportement dynamique prédit les deux fréquences de résonance caractéristiques observées expérimentalement. / The aim of this thesis was to increase the working frequency of a magneto-dielectric multilayer for ICT applications. Two structures were studied : (CoO=CoFeB)n multilayers and Py/Ru/Py trilayer. In (CoO=CoFeB)n stacks, the CoFeB resonance frequency is increased thanks to a surface anisotropy induced by the CoO oriented roughness. This roughness is generated by the deposition geometry. The resonance frequency of this system is adjustable over the entire ICT frequency range by choosing the CoO and CoFeB thicknesses. These magnetic properties are simulated by adding a demagnetizing term to the CoFeB intrinsic volume anisotropy. This term is calculated from AFM observations of CoO surface. The magnetic properties of the bilayer are not degraded in multilayers because the roughness is poorly affected by the stacking. In trilayer Py/Ru/Py, the term added to the Py intrinsic anisotropy is induced by the coupling of the two Py layers via the conduction electrons of Ru (RKKY coupling). Depending on the samples, the quadratic or antiferromagnetic coupling term is dominant. The hysteresis loop fitting leads to the coupling terms values. The dynamic properties calculus predicts the two resonance frequencies experimentally observed.

No description available.

No / A new dual-log spiral geometry is proposed for microstrip resonators, offering substantial advantages in performance and size reduction at subgigahertz frequencies when realized in superconducting materials. The spiral is logarithmic in line spacing and width such that the width of the spiral line increases smoothly with the increase of the current density, reaching its maximum where the current density is maximum (in its center for ¿/2 resonators). Preliminary results of such a logarithmic ten-turn (2 × 5 turns) spiral, realized with double-sided YBCO thin film, showed a Q.-factor seven times higher than that of a single ten-turn uniform spiral made of YBCO thin film and 64 times higher than a copper counterpart. The insertion loss of the YBCO dual log-spiral has a high degree of independence of the input power in comparison with a uniform Archimedian spiral, increasing by only 2.5% for a 30-dBm increase of the input power, compared with nearly 31% for the uniform spiral. A simple approximate method, developed for prediction of the resonant frequency of the new resonators, shows a good agreement with the test results.

Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.

Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.

Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.

This thesis investigates the impact of resonant overvoltages and their origin. Series and parallel resonances are present in any electrical grid. The frequency of which this resonance occurs is called resonance frequency. For parallel resonance, which is mainly being studied in this thesis, a high impedance peak can be found at the resonance frequency. This impedance peak in conjunction with a harmonic rich current cause a kind of temporary overvoltages called resonant overvoltages. The harmonic content of the current is high following a fault clearing in the grid, due to transformer saturation. The resonance frequency is heavily dependent on the amount of reactance present in the grid, which entail that a change in reactance causes a change in the resonance frequency. The electromagnetic transient tool PSCAD has been used to investigate resonant overvoltages following transformer energization caused by faults and switching in Stockholm. Secondly, a model was created of a grid connecting off-shore wind power to the mainland via long AC submarine transmission cables. These cables, having a high capacitance, lower the resonance frequency. Faults in this model were simulated to investigate the phenomenon of resonant overvoltages in such a grid. This was especially interesting due to Swedens planned expansion of wind power in the Baltic sea. While resonant overvoltages were found in Stockholm they were not deemed significant due to their low magnitude and longevity. However, severe resonant overvoltages were found in the off-shore wind farm model. The worst resonant overvoltages had a maximum amplitude of the 2nd order harmonic voltage of 130 kV which, while eventually damped, were significant for up to 50 periods. Lastly, the phenomenon of an increased resonance frequency during the saturation of a transformer was studied. The most severe resonant overvoltages occured in a model where the frequency scans showed a resonance frequency of 98 Hz. Indicating, caution needs to be had during EMT-studies of resonant overvoltages while choosing what resonance frequency to study.

Wound Field Synchronous Generators provide more than 95% of the electricity need worldwide. Their primacy in electricity production is due to ease of voltage regulation, performed by simply adjusting the direct current intensity in their rotor winding. Nevertheless, the rapid progress of power electronics devices enables new possibilities for alternating current add-ins in a more than a century long DC dominated technology. Damping the rotor oscillations with less energy loss than before, reducing the wear of the bearings by actively compensating for the mechanic unbalance of the rotating parts, speeding up the generator with no need for additional means, these are just few of the new applications which imply partial or total alternated current supplying of the rotor winding. This thesis explores what happens in a winding traditionally designed for the direct current supply when an alternated current is injected into it by an inverter. The research focuses on wound field salient pole synchronous machines and investigates the changes in the field winding parameters under AC conditions. Particular attention is dedicated to the potentially harmful voltage surges and voltage gradients triggered by voltage-edges with large slew rate. For this study a wide frequency band simplified electromagnetic model of the field winding has been carried out, experimentally determined and validated. Within the specific application of the fast field current control, the research provides some references for the design of the rotor magnetic circuit and of the field winding. Finally the coordination between the power electronics and the field winding properties is addressed, when the current control is done by means of a long cable or busbars, in order to prevent or reduce the ringing.