In this work we present a theoretical and computational study of the mechanism of ferroelectricity in multiferroic hexagonal manganite LuMnO3. Some structural and electronic properties are described in both paraelectric (PE) and ferroelectric (FE) phases. As theoretical and computation tool was employed the Full Potential Linear Augmented Plane Wave method, based on Density Functional Theory and embodied in WIEN2k computer code. The crystal structure of both PE and FE phases was optimized using two different types of exchange and correlation potentials. The local density approximation (LDA) and generalized gradient approximation (GGA). The lattice parameters from GGA calculation were obtained in better agreement with experimental than LDA result. Also, were analyzed two different GGA parameterizations: the so-called Perdew - Burke - Ernzerhof (PBE) and Wu - Cohen (WC). Comparing them, the result from GGA-PBE calculation is in better agreement with the experimental. After the structural optimization, the atomic positions were fully relaxed. In this step, was utilized the GGA with the PBE parameterization. The electronic properties were calculated from these optimized and relaxed structures and using the Tran and Blaha modified Becke-Johson potential. From these calculations were obtained an indirect band gap of 0,3 eV and a direct band gap of 1,6 eV in the PE and FE phases, respectively. The valence electronic density maps were obtained along the c axis of the phases PE and FE. It was observed when leave of the PE to the FE phase, the ionic character of Lu-O bonds was changed. By careful analysis of the calculated partial density of states, we showed that the loss of ionicity of the chemical bond is associated with the rehybridization of the 5dz2 - Lu with 2pz - O orbitals. This description corroborates with the model in which the mechanism of ferroelectricity of the hexagonal manganites is related with the rehybridization of the dz2 - Y or - Lu orbitals with 2pz - O s orbitals that are along the crystalline c axis. / No presente trabalho foi realizado um estudo teórico e computacional sobre o mecanismo da ferroeletricidade na manganita hexagonal multiferróica LuMnO3. Foram obtidas algumas das propriedades estruturais e eletrônicas desse composto nas fases paraelétrica (PE) e ferroelétrica (FE). Como ferramenta teórica e computacional foi utilizado o método de cálculo de estrutura eletrônica denominado de Full Potential Linearized Augmented Plane Wave que é baseado na Teoria do Funcional da Densidade e implementado no código computacional WIEN2k. Foi realizada a otimização dos parâmetros de rede usando duas diferentes aproximações para o potencial de troca e correlação. A aproximação da densidade local (LDA) e a do gradiente generalizado (GGA). Os parâmetros de rede obtidos com o cálculo GGA foram mais próximos do experimental do que aqueles obtidos usando a aproximação LDA. Para o cálculo usando a aproximação GGA foram testadas duas formas de parametrização: Perdew - Burke - Ernzerhof (PBE) e Wu - Cohen (WC). Nesse caso, o resultado obtido com a parametrização PBE é a que melhor se compara com o resultado experimental. Após a otimização dos parâmetros de rede, foram relaxadas as posições atômicas. Nessa etapa do cálculo, foi utilizada a aproximação GGA-PBE. Para o cálculo da estrutura eletrônica, foi usado o potencial modificado de troca de Becke-Johnson (mBJ). Com ele foi possível obter um band gap indireto de 0,3 eV na fase PE e um band gap direto de 1,6 eV na fase FE. Foram obtidos mapas de densidade eletrônica valência ao longo do eixo c cristalino das fases PE e FE. Observou-se, saindo da fase PE para a FE, que o caráter iônico da ligação Lu - O foi alterado. A análise da densidade de estados parciais mostrou que a perda da ionicidade da ligação química está associada à rehibridização dos orbitais 5dz2 do Lu com os orbitais 2pz do O. Esta descrição corrobora com o modelo em que o mecanismo da ferroeletricidade das manganitas hexagonais está associado à rehibridização dos orbitais dz2 do átomo R (Lu ou Y) com os orbitais 2pz dos átomos de oxigênio que estão ao longo do eixo cristalino c.

Made available in DSpace on 2014-10-09T12:42:11Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:08Z (GMT). No. of bitstreams: 0 / No presente estudo obteve-se com sucesso o compósito zeólita:magnetita usando-se como material de partida sulfato ferroso para síntese da magnetita e cinzas leves de carvão para síntese da fase zeolítica. A zeólita foi sintetizada por tratamento hidrotérmico alcalino e as nanopartículas de magnetita foram obtidas pela precipitação de íons Fe2+ em uma solução alcalina. Uma reprodutibilidade foi alcançada na preparação de diferentes amostras do nanocompósito zeolítico. O material foi caracterizado pelas técnicas de espectrometria de Infravermelho, difratometria de raios-X de pó, fluorescência de raios-X, microscopia eletrônica de varredura com a técnica de EDS, massa especifícia e área específica e por outras propriedades físico-químicas. O compósito era constituído pelas fases zeolíticas hidroxisodalita e NaP1, magnetita, quartzo e mulita das cinzas remanescentes do tratamento alcalino e magnetita incorporada na sua estrutura. A capacidade de remoção de U(VI) de soluções aquosas sobre o compósito zeólita:magnetita foi avaliada pela técnica descontínua. Os efeitos do tempo de contato e da concentração inicial do adsorbato sobre a adsorção foram avaliados. Determinou-se o tempo de equilíbrio do sistema e foram avaliados os modelos cinéticos de pseudo-primeira ordem, pseudo-segunda ordem e o modelo de difusão intrapartícula. Um tempo de contato de 120 min foi suficiente para a adsorção do íon uranilo alcançar o equilíbrio. A velocidade de adsorção seguiu o modelo cinético de pseudo-segunda-ordem, sendo que a difusão intrapartícula não era a etapa determinante do processo. Dois modelos de isotermas de adsorção, os modelos de Langmuir e de Freundlich, também foram avaliados. O modelo de Langmuir foi o que melhor se ajustou aos dados experimentais. A partir do modelo cinético e da isoterma que melhor descreveram o comportamento do sistema foi possível calcular os valores teóricos para a capacidade máxima de adsorção do U(VI) sobre o compósito zeólita:magnetita. As capacidades máximas de remoção calculadas foram de 20,7 mg.g-1 pela isoterma de Langmuir e de 23,4 mg.g-1 pelo modelo cinético de pseudo-segunda ordem. O valor experimental obtido foi 23,3 mg.g-1. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by JÚLIO HEBER SILVA (julioheber@yahoo.com.br) on 2016-11-22T18:13:24Z No. of bitstreams: 2 Dissertação - Matheus Levi Paranaguá Pinheiro - 2016.pdf: 7647037 bytes, checksum: bf9bc878e354cc06e12bc89d9e7be3c6 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2016-11-30T15:46:12Z (GMT) No. of bitstreams: 2 Dissertação - Matheus Levi Paranaguá Pinheiro - 2016.pdf: 7647037 bytes, checksum: bf9bc878e354cc06e12bc89d9e7be3c6 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-11-30T15:46:13Z (GMT). No. of bitstreams: 2 Dissertação - Matheus Levi Paranaguá Pinheiro - 2016.pdf: 7647037 bytes, checksum: bf9bc878e354cc06e12bc89d9e7be3c6 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-10-26 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Initially in this work, are presented the development and implementation of a new methodology to control the magnetic induction waveform, which was inserted into the automated measurement system for the characterization of soft magnetic materials, called SCaMMa. In the sequence, studies related to the magnetic hysteresis and to the magnetic losses, especially in silicon steels, are presented. The magnetic hysteresis in silicon steels has been analysed through the inverse version of the Jiles–Atherton classical model and through a modified one found in the literature. Concerning the determination of its parameters, the theory and the computational implementation of the heuristic method known as “Shuffled Frog Leaping Algorithm (SFLA)” have been addressed. Within this context, it was possible to investigate two drawbacks of the Jiles–Atherton model: i) the modeling of the so–called inner loops; and ii) the modeling of the minor loops. In the study of the magnetic losses in silicon steels, it was employed in this work the Bertotti´s model, which establishes the total magnetic losses division in three independent components: hysteresis losses, classical losses, and excess losses. It was investigated two versions of this model, so–called B1 and B2, in which the magnetic hysteresis losses are modeled respectively through the Steinmetz´s model and through the theory of two–portion hysteresis losses subdivision: the one so-called high induction hysteresis losses, and the other, low induction hysteresis losses. Due to some failures, a new approach was chosen reviewing two of the model coefficients calculation: the one related to the classic loss, and the other related to the excess loss. After this reviewing, the magnetic loss models could present predictions that are more exact. / Apresenta-se inicialmente neste trabalho o desenvolvimento e a implementação de uma nova metodologia para controlar a forma de onda da indução magnética, a qual foi inserida no sistema de medição automatizado para a caracterização de materiais magnéticos moles, denominado SCaMMa. Na sequência, apresentam-se estudos relativos à histerese magné- tica e às perdas magnéticas que ocorrem nesses materiais, especialmente os aços para fins elétricos. A histerese magnética em aços para fins elétricos foi abordada através da versão inversa do modelo clássico de Jiles–Atherton e através de uma versão modificada, encontrada na literatura, desse mesmo modelo. Em relação à determinação dos parâmetros desse modelo, são abordadas a teoria e a implementação computacional do método heurístico conhecido como “Algoritmo do Embaralhamento dos Sapos Saltitantes” (tradução livre de Shuffled Frog Leaping Algorithm (SFLA)). Nesse contexto, pôde-se investigar duas deficiências do modelo de Jiles–Atherton: modelagem dos laços de histerese ditos internos e modelagem dos laços de histerese menores. No estudo das perdas magnéticas em aços elétricos, empregou–se o modelo de Bertotti, o qual estabelece a divisão das perdas magnéticas totais em três componentes independentes: perdas por histerese, perdas clássicas e perdas em excesso. Foram investigadas duas versões desse modelo, os modelos denominados B1 e B2, nos quais as perdas por histerese são modeladas respectivamente através do modelo de Steinmetz e da teoria de subdivisão destas perdas em duas outras: perdas por histerese em altas e em baixas induções. Diante de alguns insucessos, optou-se por uma nova abordagem desse assunto, fazendo uma revisão do cálculo dos coeficientes relacionados à perda clássica e à perda em excesso desses modelos. Essa revisão se mostrou bastante efetiva, no sentido de que a partir de então, os modelos de previsão de perdas possibilitaram a obtenção de resultados mais exatos.

Depuis longtemps, les dispositifs ou systèmes électromagnétiques sont omniprésents dans les milieux industriel et domestique. Le circuit magnétique de ces systèmes est un des éléments clefs d’une conversion énergétique efficace. Outre l’optimisation de la géométrie du circuit magnétique, la maîtrise de l’efficacité énergétique passe par l’utilisation de matériaux magnétiques performants et par une connaissance approfondie de leur comportement, notamment sous contraintes élevées comme les températures et fréquences élevées que l’on rencontre de plus en plus aujourd’hui. Notre travail s’intègre dans le cadre des recherches menées par l’équipe matériaux du laboratoire AMPERE, notamment sur les modèles comportementaux de matériaux magnétiques. Partant de nombreuses caractérisations expérimentales en fonction de la température, nous avons développé un modèle « dynamique » adapté à différents types de matériaux ferromagnétiques, et permettant de simuler rapidement l’influence de la température sur le fonctionnement permanent et transitoire de systèmes électromagnétiques simples. Il s’appuie sur l’association des modèles d’hystérésis de Jiles-Atherton et dit « tubes de flux ». Ce modèle, et la démarche associée de couplage entre phénomènes magnétique, thermique et électrique, sont validés sur un capteur de courant et une inductance. Les résultats confirment l’importance de l’effet de la température sur les performances des systèmes, et la pertinence de disposer d’un tel modèle pour optimiser ces systèmes / Since a long time, systems and electrical devices are everywhere in the industrial and domestic environments. The magnetic core of these systems is a key for achieving energy conversion efficiency. Apart from the geometry optimization, high performance materials are mandatory for obtaining an effective energy conversion, as well as deep knowledge of their behaviour. The choice of materials is even more important when strong constraints are imposed, like high temperature and high frequency, which are more and more met nowadays. Our work is taken on in the context of the research activity on the modeling of the behaviour of magnetic materials of the “materials” team of AMPERE-Lab. Starting from a large number of experimental characterizations of materials at different temperatures, we have developed a “dynamic” model adapted to the different kinds of magnetic materials, which allows to quickly simulate the effect of temperature on the steady-state and transient regime of simple electromagnetic systems. It is founded on using Jiles-Atherton’s hysteresis models together with the so called “flux tubes”. This modelling and the associated approach of coupling electrical, thermal and magnetic phenomena are validated on a current sensor and an inductance. The results confirm the importance of the effect of the temperature on the performances of systems, and the interest of having such a model so as to optimizing these systems

Depuis une bonne dizaine d'année, l'aéronautique a entamé sa mutation vers le "plus électrique".L'objectif étant de réduire la consommation de carburant, une des contraintes majeures de ces nouvelles solutions est de réduire la masse embarquée. Les filtres dimensionnés pour les convertisseurs statiques doivent donc être optimisés au mieux vis-à-vis de ce critère, ainsi que du volume. Il y a donc un fort besoin du côté des concepteurs d’avions de savoir quels choix parmi les différentes possibilités technologiques sont optimaux, et de connaître l'impact de ces choix sur le poids, le coût global et le volume de l'équipement. Le filtre CEM représente généralement environ 30% du coût et du volume d'un convertisseur électronique de puissance. Il va de soi que le volume et/ou la masse de ces filtres doit être optimisé. L'impact de la loi de commande du convertisseur, le choix des semi-conducteurs, du packaging, câbles (longueur et intégration dans l’avion), des machines électriques,...doivent être parfaitement connus pour atteindre un dimensionnement optimal.Dans cette perspective, les objectifs de ces travaux de thèse visent à fournir non seulement une démarche méthodologique pour la modélisation haute fréquence des variateurs de vitesse dédiés aux applications aéronautiques mais aussi une approche de dimensionnement par optimisation des filtres CEM. Pour cela, un outil logiciel évolutif d’aide à la génération rapide des modèles CEM est proposé. Une description modulaire et une mise en équation automatique du modèle fréquentiel complet ainsi que des gradients en facilitent l'utilisation en procédures d’optimisation sous contraintes. L’approche présentée dans ces travaux est relativement générique : la topologie du filtre, de la structure du convertisseur, du câblage et la loi de commande peuvent être facilement recalculées, grâce à cet environnement logiciel. / The More Electrical Aircraft concept is very promising regarding energy saves, but generates new problems, and especially the emergence of new power electronics loads on the electrical network. Keeping the same level of safety in the aircraft means developing these switching mode converters in accordance with the aircraft standards, as the DO160. This is not obvious since weights of equipments are especially constrained: indeed, the objective of weight and energy save needs to be balanced with the additional weight and volume of the required EMI filters. There is thus a strong need in helping the aircraft designers to choose among the various technological possibilities, and to know the impact of these choices on the global weight, cost and volume of the embedded equipments. The EMI filter usually represents roughly 30% of the cost and volume of a power electronics converter, and it is very important to optimize it. The impact of the converter control law, semiconductors choice, interconnects realization, harness selection and placement, electrical motors characteristics… should be perfectly known in order to reach a good system design. In this perspective, the objectives of this thesis are to provide not only an approach for modelling high frequency variable speed drives dedicated to aerospace applications but also a methodology to optimize the required EMI filters. For this purpose, new architecture software dedicated to the rapid generation of EMC models is proposed. A modular description and a complete automatic model generation facilitate the use by the designer in optimization procedures thanks to automatic gradient computation.The methodology presented in this work is not specifically developed for a given application. It is a very generic approach: the topology of the filter, the structure of the inverters, interconnects and the control law can be easily recalculated, using this software environment. Consequently, the impact of all these elements on the electromagnetic disturbances can be characterized, and the EMI filter optimized.

The first part of this thesis deals with the basic division of magnetic circuits and materials which are used for their construction. The next section focuses on the description of losses in the magnetic circuit. There is a description of hysteresis losses and eddy losses. The chapter contains the theoretical basis for the mathematical description of hysteresis and eddy losses. There is an analysis of the losses caused by the first harmonious and additional losses caused by harmonics. The third part describes the measurement of losses in ferromagnetic materials. There are all methods that are used. The fourth and fifth chapter is devoted to practical measurement hysteresis losses 1. phase transformer and measuring eddy losses in the inductor using the pulse method.

In order to design a power transformer it is important to understand its internal electromagnetic behaviour. That can be obtained by measurements on physical transformers, analytical expressions and computer simulations. One benefit with simulations is that the transformer can be studied before it is built physically and that the consequences of changing dimensions and parameters easily can be tested. In this thesis a time-domain transformer model is presented. The model includes core losses as magnetic static hysteresis, eddy current and excess eddy current losses. Moreover, the model comprises winding losses including eddy currents, capacitive effects and leakage flux. The core and windings are first modelled separately and then connected together in a total transformer model. This results in a detailed transformer model. One important result of the thesis is the possibility to simulate dynamic hysteresis including the eddy current shielding in the magnetic core material. This is achieved by using Cauer circuit combined with analytical expression for static and dynamic hysteresis. Thereby, all magnetic loss components in the material can be simulated accurately. This dynamic hysteresis model is verified through experiments showing very good agreement. / QC 20101116

The physics of ultracold atomic gases has been the subject of a long standing theoretical and experimental research over the last half century. The development of evaporative cooling techniques and the realization of the first Bose-Einstein Condensate (BEC) in 1995 gave a great advantage to the field. A great experimental knowledge of the fundamental properties of BECs, such as long-range coherence, superfluidity and topological excitations, has now been acquired. On top of these advances, current research on ultracold atoms is also focusing on quantum simulations, which aim at building analogue models of otherwise difficult to compute physical systems in the lab. In this context, BECs, with their enhanced coherence, many-body dynamics and superfluid character offer a powerful platform for advances in the field. Shortly after the first realization of a BEC, research started also investigating the physics of quantum mixtures of a BECs, either composed of different atomic species or isotopes, or of atoms occupying different hyperfine states. The latter are known as spin mixtures, or spinor condensates. The presence of multiple components interacting through mutual contact interactions enriches the physics of the condensate, introducing ground states with magnetic ordering as well as spin dynamics, which can be order of magnitudes less energetic than the density one. On top of this, hyperfine states can be coherently coupled with an external resonant radiation. Interesting physics arises when the strength of the coupling is comparable with the energy of spin excitations, an example of which is given by the emergence of the internal Josephson effect. This regime has been the subject of intense theoretical studies in the past twenty years, however its experimental realization on ultracold atomic platforms have been proven to be challenging, with experiments strongly limited by coherence times of few tens of milliseconds. In fact, the small energy scale of spin excitations reflects in a high sensitivity coupling to environmental magnetic noise, which affects the resonant condition. The experimental apparatus on which I worked during my Ph.D. solve this problem employing a magnetic shield that surrounds the science chamber, attenuating external magnetic fields by 6 orders of magnitudes. During my Ph.D., I investigated the properties of a coherently coupled mixture of BEC of Sodium 23, performing different experiments in two atomic configurations. The first configuration consist of a mixture of hyperfine states, namely the |F=1, mF = -1> and |F=1, mF = +1>, coupled by a two-photon transition, which is characterized by miscibility in the ground state. Another configuration was instead realized working with a strongly immiscible mixture of |F=1, mF=-1> and |F=2, mF = -2>, realized through with a one photon transition. My first experiment was devoted to the characterization of different methods of manipulation of the coupled miscible mixture in an elongated quasi-1D geometry. In Local Density Approximation (LDA), The dynamics of the system, depends on the atom number difference, the relative phase, and coupling to mean field energy ratio, can be fully described as an internal Josephson junction. We characterized this dynamics on a sample an inhomogeneous spatial profile, developing three different protocols for state manipulations. In a second experiment, I developed a protocol to generate Faraday waves in an unpolarized miscible mixture. Faraday waves are classical non-linear waves characterized by a regular pattern, that originate in classical and quantum fluids via a parametric excitation in the fluid. Interestingly enough, this process resembles the phase of reheating of the early universe, where the oscillation of the inflaton field is thought to have excited particles out of the vacuum. In analogy with this phenomenon, the oscillation of the inflaton field can be simulated with the periodic modulation of the trapping potential. On top of this, in a spin mixture, the parametric modulation can excite either in-phase (density) modes or out-of-phase (spin) modes, as two possible elementary excitations are present in the system. By extracting the spatial periodicity of the generated pattern at different modulation frequencies, I was then able to measure the dispersion relations for both density and spin modes of the system. In the presence of the coherent coupling, when spin excitations becomes gapped, we further demonstrate the scaling of the gap with the strength of the coupling radiation. The third experiment I realized concerned the characterization of the magnetic ground state of a spatially extended immiscible mixture in the presence of the coherent coupling. The Hamiltonian of such a system is formally equivalent to a continuous version of the transverse field Ising model, which describes magnetic materials at zero temperature. In this mapping, a nonlinear interaction term arises from the ratio between the self-interaction energy and the strength of the coupling, which acts as the transverse field. As the ratio between the two quantities is varied above and below one, the ground state of the system spontaneously changes from a paramagnetic phase to an ordered ferromagnetic phase, featuring two equivalent and opposite magnetizations, a signature of the occurrence of a second order quantum phase transition (QPT). Furthermore, in the magnetic model, the degeneracy between the two ferromagnetic ground states can be broken by introducing an additional longitudinal field. In the atomic case, the role of this additional field is taken by the detuning between the coupling radiation and the resonant transition frequency of non-interacting atoms. I characterized the QPT developing protocols to manipulate the spin mixture in its spatially extended ground state, varying the longitudinal field. Leveraging on the inhomogeneity of a BEC trapped in the harmonic potential, a smooth variation of the spin self-interaction energy occurs spontaneously in space, introducing different magnetic regimes at fixed coupling strength. These protocols gave access to a characterization of static properties typical of magnetic materials, such as the presence of an hysteresis cycle. The occurrence of the phase transition was instead validated by a measurement of the magnetic susceptibility and corresponding fluctuations, which both show a divergence when crossing the QPT critical point. At last, I developed a protocol to smoothly manipulate the position of magnetic domain walls, the least energetic excitations in a ferromagnet. While the previous study focused on static properties, the last experimental investigation presented in this thesis was devoted to the study of the dynamics of the metastable ferromagnetic region of the BEC. As a result of the presence of an hysteresis cycle, it is possible to engineer states of the ferromagnetic energy landscape that are homogeneously prepared either in the global minimum, with trivial dynamics, or in the metastable, higher energy, local minima. In the latter case, a classical system should eventually decay towards the global minimum, driven by temperature fluctuations which overtop the energy barrier separating the two minima. For a quantum system described by a field theory, such as a ferromagnetic BEC, the decay towards the global minimum occurs by tunneling through the barrier, triggered by quantum fluctuations. The event of tunneling is known as False Vacuum Decay (FVD), and is of outstanding relevance also for high energy physics and cosmology, were the first theoretical models were developed. In the FVD model, the decay towards the global minimum, the true vacuum, is a stochastic process that occurs only if a resonant bubble of true vacuum is formed. Once formed, the bubble will eventually expand throughout the whole system, as the true vacuum is energetically favorable. The probability for such a bubble to form can be approximately calculated analytically in 1D, and should depend exponentially on the height of the barrier the field has to tunnel through. Due to the exponentially long time scale of the process, experimental observations of FVD were still lacking. Thanks to the enhanced coherence time of the superfluid ferromagnetic mixture, and to the precise control of the barrier height through the detuning from atomic resonance, we were able to observe the event of bubble nucleation in a ferromagnetic BEC. To corroborate the observation, I measured the characteristic timescale of the decay for different values of the control parameters. Results were successfully compared first with numerical simulation, and then validated by instanton theory.

No description available.

This thesis presents novel radio frequency microelectromechanical (RF MEMS) circuits based on the three-dimensional (3-D) micromachined coplanar transmission lines whose geometry is re-configured by integrated microelectromechanical actuators. Two types of novel RF MEMS devices are proposed. The first is a concept of MEMS capacitors tuneable in multiple discrete and well-defined steps, implemented by in-plane moving of the ground side-walls of a 3-D micromachined coplanar waveguide transmission line. The MEMS actuators are completely embedded in the ground layer of the transmission line, and fabricated using a single-mask silicon-on-insulator (SOI) RF MEMS fabrication process. The resulting device achieves low insertion loss, a very high quality factor, high reliability, high linearity and high self actuation robustness. The second type introduces two novel concepts of area efficient, ultra-wideband, MEMS-reconfigurable coupled line directional couplers, whose coupling is tuned by mechanically changing the geometry of 3-D micromachined coupled transmission lines, utilizing integrated MEMS electrostatic actuators. The coupling is achieved by tuning both the ground and the signal line coupling, obtaining a large tuneable coupling ratio while maintaining an excellent impedance match, along with high isolation and a very high directivity over a very large bandwidth. This thesis also presents for the first time on RF nonlinearity analysis of complex multi-device RF MEMS circuits. Closed-form analytical formulas for the IIP3 of MEMS multi-device circuit concepts are derived. A nonlinearity analysis, based on these formulas and on  measured device parameters, is performed for different circuit concepts and compared to the simulation results of multi-device  conlinear electromechanical circuit models. The degradation of the overall circuit nonlinearity with increasing number of device stages is investigated. Design rules are presented so that the mechanical parameters and thus the IIP3 of the individual device stages can be optimized to achieve a highest overall IIP3 for the whole circuit.The thesis further investigates un-patterned ferromagnetic NiFe/AlN multilayer composites used as advanced magnetic core materials for on-chip inductances. The approach used is to increase the thickness of the ferromagnetic material without increasing its conductivity, by using multilayer NiFe and AlN sandwich structure. This suppresses the induced currents very effectively and at the same time increases the ferromagnetic resonance, which is by a factor of 7.1 higher than for homogeneous NiFe layers of same thickness. The so far highest permeability values above 1 GHz for on-chip integrated un-patterned NiFe layers were achieved. / <p>QC 20140328</p>