Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The implementation and verification of a recently proposed Huy gens' principle in hollow lossless waveguide is described. The extended Huygens' principle is applicable to the scattering effect of arbitrary obstacles in waveguide and allows the coupling of a volume Finite Element discretization with a quasi Method of Moments surface element approach. A review of the technique is given and expressions for the two port scattering parameters are derived. The implementation is restricted to posts in rectangular waveguide, although the technique may also be applied to general scattering problems in waveguide. Finite Elements for the volume of the obstacle are selected and a basis set is proposed. The elemental finite element matrices are derived for a low and higher order basis set, while the validity of the derivations is established by considering a simple waveguide example. A coupled set of matrix equations is constructed that can be solved for the unknown surface electric and magnetic fields and the volume magnetic fields. A set of test examples is chosen to verify the implementation. The convergence behaviour is examined for two test cases. The dissertation concludes with an evaluation of the technique and recommendations for future work. / AFRIKAANSE OPSOMMING: Die implementasie en verifiëring van 'n onlangs voorgestelde Huygens beginsel in leë golfleier word beskryf. Die uitgebreide beginsel van Huygens is van toepassing op die strooiingseffek van arbitrêre voorwerpe in verlieslose golfleier en beskryf die koppeling tussen 'n volume eindige element diskretisasie met 'n oppervlakelement kwasi-moment metode. 'n Oorsig oor die tegniek word gegee en uitdrukkings vir die tweepoort strooiingsparameters word afgelei. Die implementering word beperk tot penne in reghoekige golfleier, alhoewel die tegniek op algemene golfleier strooiingsprobleme van toepassing is. Eindige elemente word gekies vir die volume van die voorwerp en 'n basisfunksie versameling afgelei van bestaande basisfunksies. Lae en hoë orde element matrikse word afgelei en die geldigheid van die afleidings word nagegaan deur 'n eenvoudige golfleier probleem op te los. 'n Gekoppelde stel matriksvergelykings word opgestel in terme van die onbekende oppervlak elektriese en magnetiese velde. 'n Aantal toetsvoorbeelde word gekies om die implementasie te verifieer. Konvergensiegedrag word ondersoek vir twee toetsgevalle. Die proefskrif sluit af met 'n evaluasie van die tegniek en aanbevelings vir verdere werk.

[pt] A caracterização do campo próximo em guias de onda ópticos torna-se indispensável quando se deseja confeccionar guias monomodo. Neste trabalho utilizou-se um sistema de medidas baseado na medida do campo próximo, para caracterizar guias de onda quanto ao seu conteúdo modal. Foram realizadas medidas do campo próximo de onda em GaAs/AlGaAs, com estruturas diferentes, para se verificar as suas características modais. Analisou-se, também, alguns parâmetros importantes nesta medida, como os alinhamentos e o ajuste do foco do sistema óptico. Baseado nos dados medidos, calculou-se o spot size dos guias nas direções horizontal e vertical, verificando-se a eficiência de acoplamento com fibras monomodo. Para se averiguar a precisão do sistema de medidas, uma fibra monomodo calibrada foi medida, verificando-se um erro de aproximadamente 1.5% nas medidas de spot size. / [en] Near field characterization of optical waveguides is extremely important in monomode waveguides production. This work has use a measurement system based on the near field measurement, for characterizing the modal contents of waveguides. In order to verify the modal characteristics of two GaAS/AlGaAs waveguides, with different structures, near fiels measurements were made. Important parameters, such as the alignment and the focal adjustment of the aoptical systems, were also analyzed. Using the results from the measurements, it was calculated the spot size of the waveguides in the horizontal and vertical directions, verifying the coupling efficiency with monomode fibers. A calibrated monomode fiber was measured to analyze the system precision. On using this measurement as a reference parameter a high precision was observed

[pt] O desenvolvimento de moduladores externos é fundamental já que em decorrência do efeito de chirp em altas freqüências, a modulação direta de lasers fica prejudicada. Nesta tese projetamos uma estrutura de modulador de amplitude utilizando o efeito Stark em semicondutores para ser aplicado em sistemas de telecomunicação de altas taxas. Na estrutura semicondutora proposta utilizou-se a eletro-absorção em poços quânticos múltiplos de OnGaAs/InAlAs. Diferentes figuras de mérito do dispositivo passivo e ativo foram analisadas. Na simulação do comportamento do dispositivo como guia de onda foram utilizados os seguintes métodos: Método do Índice Efetivo e Método de Propagação de Feixe. A aplicabilidade desses métodos foi testada numa estrutura Rib de GaAs/AlGaAs e os resultados confrontados com medidas feitas em laboratório. Estando os resultados experimentais de acordo com os resultados obtidos através da simulação, os mesmos métodos foram utilizados na avaliação da estrutura do modulador de amplitude proposta. O comportamento resultante do guia correspondente às características almejadas. / [en] The development of external modulators is fundamental since the presence of chirping deteriotates the direct modulation of laseres ati high frequencies. In this work a project of an amplitude modulator for high bit-rate telecommunication systems using the Stark effect in semiconductors was undertaken. In the proposed semiconductor structure the electro-absorption in InGaAs/AnAlAs multiple quantum wells was used. Different figures of merit of the passive and active device were analysed. In the simulation of the device performance as a waveguide the following methods were applied: effective Index Method and Beam Propagation Method. The applicability of these methods were tested on a GaAs/AlGaAs rib structure and the results were compared with measurements done in the laboratory. The experimental results were in completed accord with the simulation. Therefore, the same methods were used to evaluate the proposed amplitude modulator structure. The resulting performance of the waveguide corresponds to the desired characteristics.

[pt] Reflectometria Ótica de Baixa Coerência (OLCR) é uma importante técnica não-destrutiva para a caracterização de guias de onda óticos. Este trabalho apresenta um estudo sobre a multiplicação de soluções que aparecem com uma nova configuração, que coloca o dispositivo fora dos braços do interferômetro. Duas técnicas foram desenvolvidas para resolver esse problema. Uma delas é baseada na correlação de medidas feitas com o dispositivo em duas posições diferentes. A outra técnica elimina a dualidade pela modulação da fase das reflexões provenientes do dispositivo. Ambas as técnicas eliminaram os picos indesejáveis satisfatoriamente, tornando mais fácil a observação das reflexões. A resolução não foi alterada pela modulação, e um elevada sensibilidade foi obtida. Um método para medidas de atenuação, baseado em sistemas de OLCR, foi apresentado. Se o coeficiente de reflexão for bem conhecido, o seu uso para medidas em guias de onda, tais como moduladores eletro-óticos, pode ser bastante interessante. / [en] Optical Low Coherence Reflectometry (OLCR) is na important non-destructive method for characterization of optical waveguides. This work presents a study of the plurality of solutions that appear with a new configuration, which places the device out of both arms of the interferometer. Two techniques were developed to solve this problem. One of them is based on the correlation of measurements made with the device in two different positions. The other technique removes the ambiguity by modulating the phase of the reflections from the interferometer. Both techniques have eliminated the undesirable peaks sucessfully, making the observation of the reflections more easy. The resolution was not changed by the modulation, and a high sensitivy was achieved. A method for attenuation measurements, based on OLCR systems, was presented. If the reflection coefficient is well know, its use for measurements of optical waveguides, such as modulators, could be very interesting.

Made available in DSpace on 2015-12-10T14:24:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-05-29. Added 1 bitstream(s) on 2015-12-10T14:31:10Z : No. of bitstreams: 1 000853520.pdf: 2749056 bytes, checksum: aeead8823ebd2b93063ca4406bc23b07 (MD5) / O estudo da interação de ondas elásticas em sólidos imersos em um fluido tem sido reconhe- cido como um meio viável para caracterização de líquidos. As ondas guiadas em estruturas tipo placa possuem a característica de serem multimodais e dispersivas. Estas características introduzem mais informação ao processo de medição, além de tornar a análise teórica e a inter- pretação física dos resultados experimentais mais envolventes. Quando a placa está em contato com o fluido, há uma forte atenuação devido às ondas de fuga e perdas viscosas no fluido. Esta característica pode ser explorada para a caracterização de líquidos, devido à alta sensibilidade associada à interação entre a onda e o fluido. Pensando nesta particularidade estudou-se o modo quase Scholte, que é um tipo de onda de interface cuja energia está confinada perto da região da superfície da placa. A análise deste modo propagante é uma alternativa atraente para se determinar a velocidade volumétrica longitudinal e a atenuação no líquido, o que proporciona valiosas informações sobre as propriedades do fluido. Neste trabalho, as ondas guiadas (mo- dos de Lamb e quase Scholte) são teoricamente descritas por um sistema de equações obtido do modelamento de uma placa sólida homogênea em contato com um fluido viscoso, o qual é descrito usando a equação de Navier-Stokes. As curvas de dispersão e atenuação das ondas de Lamb e do modo quase Scholte são obtidos numericamente como soluções das equações carac- terísticas. Experimentos foram realizados visando mensurar a velocidade de fase e a atenuação para os modos de Lamb e quase Scholte, mostrando a existência de bandas de frequências de baixa atenuação. Estas medições foram obtidas usando transdutores longitudinais de banda larga acoplados a prismas de acrílico, excitados com pulsos senoidais e posteriormente analisa- dos em tempo-frequência / The study of the interaction of elastic waves in solids immersed in a fluid has been recognized as a suitable method for fluid characterization. Guided waves in plate-like structures, are mul- timodal and dispersive. These characteristics provides more information in the measurement process. In addition, the theoretical analysis and physical interpretation of the experimental results become more involved. When the plate is in contact with a fluid, there is strong attenu- ation due to Leaky waves and viscous losses in the fluid. This characteristic can be explored for the fluid characterization, due to the high sensitivity associated to the interaction between the wave and fluid. From this feature a study about the quasi-Scholte mode was done, which is a kind of interface wave and its wave energy in the fluid is confined in the region close to the surface of the plate. The analysis of this propagating mode is an attractive alternative to determine the bulk longitudinal velocity and attenuation in the liquid, which provide valuable information about the liquid properties. In this work, guided waves (Lamb and quasi-Scholte modes) are theoretically described by a system of equations obtained by modeling a homo- genous solid plate in contact with a viscous fluid, which is modeled using the Navier-Stokes equation. The dispersion and attenuation curves of Lamb waves and quasi Scholte mode are numerically calculated from the characteristic equations. Experimental measurements were conducted in order to obtain the phase velocity and attenuation for the Lamb waves and quasi Scholte mode showing the existence of low attenuation frequencies bands. These measurements were obtained by using longitudinal wide band transducers coupled to acrylic wedges, excited with senoidal pulses and then time-frequency analysed. In order to evaluate the potential use of this result in NDT applications ultrasonic images were also ...

[pt] Neste trabalho, o efeito de um obstáculo cilíndrico do tipo poste em guias de ondas retangulares e circulares é o objeto de estudo. Considerando-se um poste metálico em um guia de ondas retangular, utiliza-se o método dos momentos e diádicas de Green como técnica de obtenção de soluções. Utilizando a mesma metodologia, estada-se um poste metálico em um guia de ondas circular. A análise de um poste dielétrico em guias de ondas retangular e circular é feita através da técnica perturbacional. / [en] In this work, the effect of a cylindrical obstacle such as a post in rectangular and circular waveguides is the subject of study. Considering a metallic post in a rectangular waveguide, the Method of Moments and the Dyadic Green s Functions are applied to obtain the solutions. The same methodology is used to study a metallic post in a circular waveguide. A perturbational analysis is carried out to study a dielectric pos in retangular and circular waveguides.

Photoemission Electron Microscopy (PEEM) is a versatile tool that relies on the photoelectric effect to produce high-resolution electron images. Ultrafast pulse lasers allow for multi-photon PEEM where multiple visible or IR photons excite a single electron in a nonlinear process. The photoelectron yield in both cases is related to the near-field region of electromagnetic fields at the surface of the sample. We use this ability here to analyze wave propagation in a linear dielectric waveguide with wavelengths of 410 nm and 780 nm. The propagation constant of the waveguide can be extracted from interference patterns created by light propagating in the waveguide and incident light. Various properties like the polarization dependence of the propagation can be analyzed. The electromagnetic field interaction at the boundaries can then be deduced, which is essential to understand power flow in wave guiding structures. These results match well with simulations using finite element techniques as well as electromagnetic theory.

Thesis (DPhil (Social Work))--University of Pretoria, 2005. / Social Work / unrestricted

In training programs designed to help immigrant women adapt to Canada, drop-out rates are frequently high and attendance is often low. Investigating some reasons behind this observation was the motivation for this thesis. A literature review revealed that curricula used in existing programs are often developed from experts' understanding of immigrants' needs; research on immigrant women's curricular needs as perceived by themselves is virtually nonexistent. An objective of this thesis was to address this knowledge gap. This study inquired into what curricular needs immigrant women have, how these needs differ, and what relationship exists between the women's backgrounds and their curricular needs. A questionnaire was developed and validated by an expert panel, and then administered to graduates from an orientational training program. Post-survey interviews were conducted. Data were analyzed using frequency distribution, cluster analysis, multivariate analysis of variance (MANOVA), factor analysis, and linear discriminant analysis. It was found that the program, although well received, did not reflect the curricular needs perceived by the immigrant women themselves. Life skills instruction was unwanted by many students while English and computer lessons were in demand. A desire to regain higherquality jobs partially explained the women's curricular needs. / Education, Faculty of / Curriculum and Pedagogy (EDCP), Department of / Graduate