Thesis (M.S. in mechanical engineering)--Washington State University, May 2007. / Includes bibliographical references (p. 88-89).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 174-181). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 134-141).

This thesis evaluates standard EMC aircraft equipment specifications highlighting their weaknesses and suggesting modifications, some of which have already been included in the new generation of specifications now being introduced. The relationship of the equipment level EMC test to the whole aircraft EMC test is discussed and improvements to this latter activity, which have been developed as a result of the work programme described in this thesis, are presented and evaluated.

A finite difference algorithm for solving the forward modelling problem of geo-electromagnetic induction in three-dimensional structures has been developed in this thesis. Novel features of the method include the incorporation of a thin sheet of anomalous conductance at the surface of an otherwise quite general three-dimensional structure in which the anomalous region is allowed to approach two-dimensional configurations at infinity; the use of magnetic rather than the electric field components for obtaining the solution; the use of integral boundary conditions at the top and bottom of the model; and the application of new cell-integral finite difference equations to the main body of the model. The algorithm has been tested for synthetic models against results delivered by existing two and three dimensional modelling programs which are already well established. The results are found to be very satisfactory. Applications of the algorithm have been shown for two cases. First, the dependence of the induction vectors on the period ranging from 10 to 10000 s has been studied for a model with two perpendicular lateral conductivity contrasts; the directions of induction vectors vary from site to site reflecting the combined effect of the two perpendicular contrasts. In the second case, the distortion effect due to small surface inhomogeneities over a buried 2D anomaly was studied using induction vectors and difference vectors. There is evidence of mutual coupling in a certain region which invalidates a simple subtraction of the vectors to reveal the form of the buried anomaly, but elsewhere the procedure appears to be quite valid. Since surface anomalies can be simulated by an anomalous thin sheet over the general 3D structure, it is suggested that this algorithm could be very useful for testing the validity of existing schemes for impedance tensor decompositions used in MT studies when surface anomalies are thought to be distorting the real data. / Graduate

La capacité de pénétration des ondes électromagnétiques (OEM), généralement non destructive, dans les matériaux ou tissus permet de sonder les milieux étudiés. En termes de santé publique, améliorer la qualité de vie est devenu un objectif majeur de la société actuelle. Des applications de sondage par OEM de divers milieux ou tissus dans le domaine biologique présentent un intérêt majeur dans les opérations de diagnostic et dans les opérations thérapeutiques. Les travaux de cette thèse abordent le vaste domaine des applications biomédicales, des interactions micro-ondes/radiofréquences et de la matière. Ces travaux de thèse se focalisent sur l’univers émergeant de l’Imagerie par Résonnance Magnétique (IRM) à Ultra-Haut Champ. Le premier objectif est de développer un fantôme anthropomorphique de tête humaine ou il faut prendre en compte les propriétés électromagnétiques et les temps de relaxation caractéristiques de chaque tissu. Cela permet d’obtenir une estimation précise des niveaux de DAS pour l’être humain et une notion des formations de hotspots lors d’un examen IRM haut-champ.Le deuxième objectif dans le domaine des IRM à très haut champ est l’étude et la fabrication des dispositifs d’homogénéisation de champ permettant ainsi d’éclaircir les zones d’ombres. Ce processus, dénommé Dielectric Shimming, est basé entre autre sur l’utilisation d’éléments discrets à hautes permittivités appelés pads. Ces pads sont composés de matériaux diélectriques à fortes permittivités, comme des solutions aqueuses de Titanate de Baryum, afin de focaliser le champ dans les zones initialement sombres de l’image de l’IRM (dans cas du cerveau : le cervelet et les lobes temporaux). / The penetration capacity of the electromagnetic (EM) waves in matter or biological tissues allows exploring media non-destructively. Concerning the public health sector, improving the quality of life has become one of the greatest concerns of nowadays society. EM wave research on different media and biological tissues shows a great potential for diagnostic applications and eventually for therapeutically applications. In this doctoral thesis, we focus on the vast domain of the biomedical applications of wave-matter interactions, based on the knowledge of the electromagnetic properties of matter, the complex permittivity and the conductivity. On a first instance, we address the emerging domain of ultra-high field MRI (Magnetic Resonance Imaging), which nowadays puts effort into the clinical implementation of 7T devices. Firstly our purpose is to produce an anthropomorphic head model, composed of the brain’s different layers, and taking into account the electromagnetic properties and the proton relaxation times inherent to each tissue. These realistic head models allow to evaluate the newly developed protocols for these ultra-high field devices. Secondly, we have studied and developed field homogenization devices, which allow brightening the shadow areas displayed in some MRI images, such as the cerebellum and the temporal lobes in brain imaging at 7T. This procedure, named Passive Shimming, is based on the use of high permittivity dielectric pads composed of Barium Titanate, which focalize the field to the areas where normally the wavelength in insufficient to generate a homogeneous signal distribution.

M.Ing. (Electrical and Electronic Engineering) / This work reports on a study in the fields of "High power pulsed power supplies and electromagnetic pulse compression". A background discussion on the application of pulsed power on lasers is given. Pulse compression and high power pulsed power supply configuration is described. The work concentrates on simultaneous energy transfer electromagnetic pulse compression which is a technique used to achieve a saving of core material in a pulse compressor. An analytical expression for the saving was derived and verified experimentally. This result is applied in different pulse compressors designed for the pulsed power supplies of copper vapour lasers. The test results are provided and discussed. A windfall from the practical work is a design solution for the voltage sharing compensation network needed when switching semiconductors in series.

M.Ing. / Open-wire telecommunications were developed in the 19th and early 20th centuries without any consideration of the deleterious effects of power lines; compatibility problems were later caused by the proximity of power lines and telephone lines. The coexistence of such systems requires careful planning in terms of energy coupled to the telephone lines; this induction can cause interference, as well as dangerous overvoltages in telephone circuits, and requires detailed studies of the effects of coupling between high voltage lines and telephone systems to be done. In terms of inductive co-ordination in South Africa, the minimum separation distances between high voltage power lines and communication systems are calculated only for power frequency and lower order harmonics (up to the 13th). The aim of the study was to explore the agreement between theory and measurement for frequencies from 50 Hz to the high order harmonic range of 4 kHz; this makes it possible to extend existing methods for predicting compatible separations to cases where high order harmonics (up to the 73rd) are present (balanced and unbalanced) on a 132 kV power line feeding a large aluminium smelter plant.

Abstract Design and manufacturing techniques of printed circuit boards (PCB's) have advanced from early one or two-layer structures to the multilayer boards where ten or more layers are no longer uncommon. These give additional routing space, potential decrease in device size and various design possibilities like solid ground and power planes. Unfortunately multilayer boards are vulnerable to high coupling between signal vias especially due to PCB resonances. In this study via crosscoupling is investigated on multilayer PCB's. Special attention is given to the coupling due to resonances and vertically aligned blind vias. Problem is approached from the electromagnetic compatibility (EMC) point of view and high accuracy of measurements or models is not the objective. Instead ways to increase isolation are considered important. EMC is considered to include internal functionality of the device. Analytical methods are used to calculate resonant frequencies, fields and quality factors for simple rectangular structures. The PCB cavity is reduced to two-dimensions for numerical calculation of same quantities. Aplac finite-difference time-domain simulator is used to model coupling due to PCB resonances. Isolation between vertically aligned blind vias is estimated analytically. A quasi-static numerical model is used to study a coaxial via structure. Multilayer test boards are constructed for measurement purposes. Simplified resonator structures on two-layer boards are used to test different methods to increase isolation. Measurements show that high coupling between vias may occur due to PCB resonances. This leads to the situation, where previously used isolation methods between vias are not necessarily effective enough. Several means to reduce effects of PCB resonances are described in this study. Measured and modelled results agree well from an EMC point of view. Coupling due to vertically aligned blind vias is also shown to be high. A simple capacitance model may be used to approximate this up to frequencies where the dynamic wave nature of the board starts to be important. From a PCB designer's point of view these results mean that when the board size is not small compared to the wavelength, there is a possibility of resonances and reduction methods have to be taken into account. Also placement of the vias have to be carefully selected especially if blind or buried vias are used.

M.Ing. (Electrical and Electronic Engineering) / Recent world events such as the fall of Communism. attempts at the unification of Europe and the reaching of the most extensive international trade agreement yet (GATT ::: General Agreement on Trade and Tariffs). have all contributed to the expansion of world markets as well as a marked intensification in the competition in those markets. Rivalry in the market for power electronic equipment is as relentless as in any other. Strict regulations with regard to Electromagnetic Interference (EMf) and Electromagnetic Compatibility (EMC) apply in Europe and compliance with these standards is legally enforced. In South Africa, compliance with such standards is merely recommended, hence local manufacturers have not yet considered these phenomena seriously enough to pose a threat to their European opposition. The two main causes of EMI are switching action, which is such an integral part of power electronics, and the excitation of parasitic circuit elements. This thesis describes the investigation carried out to determine the effect of certain layout and construction parameters on the generation of EMf. Parasitic loop inductances, self-capacitances of coils and the ground connection of heat sinks were examined in the process. A test convener containing a full-bridge converter perfonning DC·DC conversion, was built. These converters are important building blocks for equipment such as uninterruptible power supplies. One configuration of this converter was designated as the reference configuration. For every modification of a layout or construction parameter its effect on the interference spectrum was determined through a comparison with the measured interference spectrum of the reference configuration. The use of snubbers and the minimisation of the self-capacitances of inductors in an output filter effected a marked decrease in the measured interference spectrum (approximately 10 dB or a third less). Certain loop inductances have to be minimised in the design stages through proper layout of conveners, and heat sinks should preferably be grounded through high resistances. Paying due attention to these aspects in the design of power electronic converters can aid in decreasing the size and cost of bulky, expensive EMf filters required to meet the standards. It could give local manufacturers a considerable advantage over their overseas competitors.