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One of the most exciting studies of contemporary physics is that of high temperature superconductor (HTS). Since its discovery, a large body of experimental and theoretical work by various groups has attempted to achieve a common understanding of this phenomenon. One of the main driving forces for applications centres on the possibility of new and improved microwave devices based on HTS materials, mainly due to the large reduction in the surface resistance that HTS has to offer. However, various problems need to be addressed before the use of HTS materials can be justified, for example fundamental issues such as the nonlinearity of these materials with respect to microwave power, which form the basis of this work. Microwave measurements were conducted on four magnetron sputtered and three laser ablated, Icm2 YBCO thin films, grown on LaAI03 and MgO substrates, respectively, employing the dielectric (rutile) resonator and coplanar resonator techniques. The low power response of the films was initially analysed, looking for clues to the underlying pairing mechanisms in these films. Power dependence and microwave intennodulation distortion (lMD) measurements were conducted between 12 K to 60 K to investigate the nonlinear response of the films, both in zero and finite dc (10 mT) fields. The effect of patterning on the microwave response of the films was also studied. From these measurements, it was observed that the microwave losses of these films are extrinsic in nature, probably a consequence of weak links/defects, and the results also show that films fabricated from the same technique can have significantly varying quality.

Boundary value problems required for modelling plane wave propagation in electrically anisotropic and inhomogeneous media relevant to the surface impedance methods in electromagnetic geophysics are formally posed and treated. For a homogeneous TM-type wave propagating in a half space with both vertical and horizontal inhomogeneities where the TM-type wave is aligned with one of the elements of the conductivity tensor, it is shown using exact solutions that the shearing term in the homogeneous Helmholtz equation for inclined anisotropic media: [Equation 1], unequivocally vanishes and solutions need only be sought to the homogeneous Helmholtz equation for biaxial media: [Equation 2]. This implies that those problems posed with an inclined uniaxial conductivity tensor can be identically stated with a fundamental biaxial conductivity tensor, provided that the conductivity values are the reciprocal of the diagonal terms from the Euler rotated resistivity tensor: [Equation 3], [Equation 4], [Equation 5]. The applications of this consequence for numerical methods of solving arbitrary two-dimensional problems for a homogeneous TM-type wave is that they need only to approximate the homogeneous Helmholtz equation and neglect the corresponding shearing term. The self-consistent impedance method, a two-dimensional finite-difference approximation based on a network analogy, is demonstrated to accurately solve for problems with inclined uniaxial anisotropy using the fundamental biaxial anisotropy equivalence. The problem of a homogeneous plane wave at skew incidence upon an inclined anisotropic half space is then formally treated. In the half space, both TM- and TE-type waves are coupled and the linearly polarised incident TM- and TE-type waves reflect TE- and TM-type components. Equations for all elements of the impedance tensor are derived for both TM- and TE-type incidence. This offers potential as a method of predicting the direction of anisotropic strike from tensor impedance measurements in sedimentary environments.

Part I of this dissertation is concerned with the problem of the magnetic field dependence of the surface impedance of superconductors, with particular reference to tin. In chapter 1 the predictions of the simple theory for the behaviour of the surface impedance for different frequencies and fieid configurations are described and compared with the results of previous experiments. Chapter 2 deals with the experimental side of the present work, where a frequency of 170 Mc/s was used, and in chapter 3 the results obtained are discussed. In chapter 4 the attempts which have been made to account theoretically for the experimental observations are reviewed. Part II of the dissertation is concerned with another problem in superconductivity, namely the behaviour of superconducting systems partitioned by thin barriers of substances which in bulk are not superconducting. The theory of such systems is developed, the consequences investigated in some detail and the present experimental situation reviewed.

In this report the analysis of microstrip electrodynamic structures on basis of high-temperature superconductors is carried out and a mathematical model of microstrip devices with lumped and distributed nonlinear properties is created. For this purpose nonlinear integral equations method and method of moments are used. In the issue of the work a SHF filter based on the equivalent circuit of elements with lumped parameters is also studied. It is ascertained that the received mathematical model allows to achieve more proper results of modeling on compensation of variation of current-density distribution nearby the edges of conductor break.

The aim of the thesis is to describe EBG substrate and exminate his influence on some types of antennas and choose one of them for realization. In first part this thesis describes the paramaeters of antenna in generall, in the second part is dedicated to introduction with EBG substrate mainly on the surface with the high impedance (HIES). The third part deals with the simulations of microstrip patch antennas with EBG substrate and without EBG substrate. In the last parts was designed and optimized antenna using superstrate.

Les Surfaces à Haute Impédance (SHI) ont été largement étudiées pour améliorer toutes sortes de performances des antennes, comme le gain, le facteur de qualité, les formes et dimensions. L'objectif de cette thèse est de modéliser les structures de SHI et de caractériser leurs performances en vue de futures applications aux antennes.Après une brève introduction aux structures SHI et une étude de quelques modèles analytiques fréquemment traités dans la littérature, deux nouvelles méthodes numériques sont proposées pour calculer l'impédance de surface de structures SHI. Ces deux méthodes (dites « méthode du flux de Poynting » et « méthode <E>/<H> ») sont validées sur des structures symétriques, puis mises en service sur des structures de SHI asymétriques. Elles sont également validées par comparaison de résultats analytiques, numériques et expérimentaux.Nous présentons ensuite un modèle équivalent basé sur l'idée de remplacer les structures hétérogènes de SHI par une surface homogène, caractérisée par son impédance surfacique. Ce modèle nous permet d'avoir une prédiction avec un temps de calcul et une occupation de mémoire PC largement réduits. / High impedance surfaces (HIS) have proved good candidates for antenna miniaturization or antennas performance improvement. Within a certain frequency band, they can enhance the gain of an antenna while simultaneously suppressing the unwanted surface waves.In this thesis, the focus of our work is on numerical modeling of these structures by using the finite element method (FEM) based on edge elements.One of our contributions is that we propose two new numerical methods (the Poynting flux method and <E>/<H> method) to calculate the surface impedance not only for HIS structures with symmetric geometries, but also for those with asymmetric geometries. These two numerical methods have been validated by comparing analytical, numerical and experimental results.Another significant contribution of the thesis is that we introduce an equivalent model, based on the idea of replacing the heterogeneous HIS structures by a homogeneous surface, characterized by its surface impedance. Compared with the normal model, this equivalent model can save computing time and memory space.

Environmental noise has for decades been a well known problem, especially in urban areas. As noise requirements for vehicles are sharpened, noise reducing concepts are needed in early design stages requiring accurate simulations to support the design. Specifically for optimization of noise treatments, the absorber performance must be simulated correctly. So called noise encapsulations are placed below the powertrain on heavy vehicles to enclose the engine and reduce noise radiation. The attenuation of the absorbers on these shields must be represented correctly in simulations, even in environments with complex sound field, cooling flow and high temperature variations which may affect the absorber performance. This thesis studies the performance variation due to different absorber representations and due to these factors and how to include this in simulations. It is shown that the material representation significantly affects the attenuation performance in the simulations. Assuming locally reacting absorbers neglects the full interaction between the sound field and the material, which was shown to affect the noise reduction considerably. A measurement method to determine the angular dependent surface impedance was evaluated. It was shown sensitive to small samples and a method to improve accuracy was suggested. Including the angular dependence, either by full resolution or an angular dependent impedance, the field-absorber interaction is included in the simulations and more accurate results are obtained. The influence of flow and temperature fields on the absorber performance was also investigated. A method to include these effects was developed and the attenuation performance shown significant, especially for materials with bulk reaction. In conclusion, thorough knowledge of the material behavior and the field in the applications is required to choose appropriate material representation to enable reliable simulation results.​ / <p>QC 20160311</p>

Ces dernières années, un intérêt croissant est porté aux réflecteurs rétro-directifs aplatis dans le but de remplacer le réflecteur diédrique conventionnel, trop encombrant pour de nombreuses applications. Dans un premier temps, cette thèse étudie deux techniques différentes permettant de réduire l’épaisseur d’un réflecteur diédrique. L’Optique de transformation modifie la constitution matérielle de son volume intérieur alors que la modulation d’impédance de surface introduit une distribution d’impédance à sa surface. On examine également la possibilité de combiner ces deux techniques pour tirer le meilleur parti de chacune d’elle. La deuxième partie de cette thèse étudie l’origine des réflexions parasites pour les panneaux utilisant la modulation d’impédance de surface et propose de nouvelles règles de conception pour atténuer leurs niveaux. Finalement, une mise en oeuvre pratique est proposée pour une modulation d'impédance de surface généralisée qui utilise des impédances complexes et surpasse les performances de la modulation d’impédance classique. / In recent years, increasing interest incompact reflectors with retrodirective response is perceived since the conventional dihedral reflector is too bulky to be integrated within most applications. First, this thesis investigates two different techniques that might lead to lower profiles of the dihedral reflector. It explores the use of Transformation Optics that modifies the filling volume of such a device and Surface Impedance Modulation that introduces an impedance distribution over its surface. It also inspects the possibility of combining those two techniques to take benefit of their complementary advantages. The second part of this thesis investigates the source of parasitic lobes for surface impedance modulated panels and proposes new design rules to mitigate their levels. Finally, it also proposes a practical implementation for a specific setting of the generalized surface impedance modulation that makes use of complex impedances and outperforms a panel implementing the classical modulation.

Exact analytical solutions for the quasistationary electromagnetic fields in the presence of conducting objects require the field solutions both internal and external to the conductors. Such solutions are limited for certain canonically shaped objects but are useful in testing the accuracy of various approximate models and numerical methods developed to solve complex problems related to real world conducting objects and in calibrating instruments designed to measure various field quantities. Theoretical investigations of quasistationary electromagnetic fields also aid in improving the understanding of the physical phenomena of electromagnetic induction. This thesis presents rigorous analytical expressions derived as benchmark solutions for the quasistationary field quantities both inside and outside, Joule losses and the electromagnetic forces acting upon a conducting spheroid placed in the proximity of a non-uniform field produced by current-carrying turns. These expressions are used to generate numerous numerical results of specified accuracy and selected results are presented in a normalized form for extended ranges of the spheroid axial ratio, the ratio of the depth of penetration to the semi-minor axis and the position of the inducing turns relative to the spheroids. They are intended to constitute reference data to be employed for comprehensive comparisons of results from approximate numerical methods or from boundary impedance models used for real world conductors. Approximate boundary conditions such as the simpler perfect electric conductor model or the Leontovich surface impedance boundary condition model can be used to obtain approximate solutions by only analyzing the field external to the conducting object. The range of validity of these impedance boundary condition models for the analysis of axisymmetric eddy-current problems is thoroughly investigated. While the simpler PEC model can be employed only when the electromagnetic depth of penetration is much smaller than the smallest local radius of curvature, the results obtained using the surface impedance boundary condition model for conducting prolate and oblate spheroids of various axial ratios are in good agreement with the exact results for skin depths of about 1/5 of the semi-minor axis when calculating electromagnetic forces and for skin depths less than 1/20 of the semi-minor axis when calculating Joule losses.