Thesis (M.Eng.(Electronic Engineering))--University of Pretoria, 2007. / Summaries in Afrikaans and English. Includes bibliographical references (leaves 75-78).

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xiii, 122 p.; also includes graphics Includes bibliographical references (p. 80-94). Available online via OhioLINK's ETD Center

Thesis (Ph.D.) - University of St Andrews, May 2008.

[pt] Lentes eletromagnéticas têm sido usadas desde a década de 50 como forma de se obter uma antena com apontamento eletrônico e alta diretividade, capaz de operar numa vasta faixa de freqüências. Por este motivo, tornaram-se populares, principalmente em aplicações de Guerra Eletrônica. Entretanto, uma de suas desvantagens é que, a cada momento, apenas uma fonte emissora é usada para um certo apontamento. Esta tese propõe um novo tipo de lentes geodésica em que se emprega uma distribuição de fontes uniforme sobre a entrada da lente, sendo que todas elas sempre emitem com a mesma potência, independentemente da direção escolhida para o feixe. Os mesmos objetivos são atingidos - diretividade, ampla faixa de freqüências de operação e apontamento eletrônico. Assim, todas as fontes contribuem para a potência total irradiada, com a mesma amplitude, sendo o apontamento obtido pela adequada escolha da fase de cada uma destas fontes. Acrescenta-se que tal dispositivo possui menor queda de desempenho, numa situação de falha de uma ou mais fontes. Dois modelos teóricos para a análise e projeto da estrutura - um baseado na ótica geométrica e outro em técnicas modais - são apresentados e comparados. / [en] Electromagnetic lenses have been applied since early 50´s as a means of obtaining an electronic steerable antenna with high directivity and broadband range of operation. For this reason, they have became very popular in Electronic warfare applications. Some of their weakness, however, would be the fact that only one feed point (supply) - and all the associated circuitry - can be used at a time, in order to generate a single bean in the radiated field. The purpose of this these is to propose a new kind of geodesic lens in which the same goals are obtained (high directivity, broadband range of frequencies, and electronic steering) but with an uniform distribution of feeding along the lens input, all the supplies used at all times, no matter what the direction chosen for the output bean. Therefore, all the feeding points are radiating the same amount of power (same amplitude), the electronic steering is obtained by properly setting the phases of the several supplies at the input of the lens. Moreover, the device proposed here has less degradation of performance when one or a few supplies go down. Two theoretic models for the analysis and design of such device - one based on the geometric optics and the other based on modal techniques - are also provided and compared.

<p> Sediment samples were taken from the exposed facies of two quarries north of Burford Ontario. The samples were then dry sieved and the results were plotted as frequency histograms to show the type and quantity of sediment present. Moreover, measurements of soil tongues, sand lenses and strata depths were recorded to provide a comprehensive understanding of the depositional history and processes.</p> <p> The above research was then combined with the present day comprehension of the depositional history of southern Ontario. The conclusions reached in this paper are useful, as they contribute and improve the understanding of the depositional history of southern Ontario.</p> / Thesis / Candidate in Philosophy

No description available.

Contact lens production requires high accuracy and good surface integrity. Surface roughness is generally used to measure the index quality of a turning process. It has been an important response because it has direct influence toward the part performance and the production cost. Hence, choosing optimal cutting parameters will not only improve the quality measure but also the productivity. In this study, an ONSI-56 (Onsifocon A) contact lens buttons were used to investigate the triboelectric phenomena and the effects of turning parameters on surface finish of the lens materials. ONSI-56 specimens are machined by Precitech Nanoform Ultra-grind 250 precision machine and the roughness values of the diamond turned surfaces are measured by Taylor Hopson PGI Profilometer. Electrostatics values were measured using electrostatic voltmeter. An artificial neural network (ANN) and response surface (RS) model were developed to predict surface roughness and electrostatic discharge (ESD) on the turned ONSI-56. In the development of predictive models, turning parameters of cutting speed, feed rate and depth of cut were considered as model variables. The required data for predictive models were obtained by conducting a series of turning test and measuring the surface roughness and ESD data. Good agreement is observed between the predictive models results and the experimental measurements. The ANN and RSM models for ONSI-56 are compared with each other using mean absolute percentage error (MAPE) for accuracy and computational cost.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Phase shifting interferometry is one of the most promising methods for testing aspheres. However, one will encounter the following problems when it is applied to test an asphere: (1) very tight fringes produced by a strong asphere exceed the test system's resolution, (2) a test wavefront suffers from system aberrations of the interferometer that cause measurement errors, and (3) the wavefront immediately after reflection does not necessarily represent the shape of the test asphere. This thesis used a high density array sensor to detect the dense fringes. In order to solve the system aberration and the ray retrace problems, it is necessary to incorporate a ray trace code and phase shifting interferometry. This measurement principle was applied for an aspheric surface whose asphericity was 100 waves. A phase shifting Fizeau interferometer was incorporated with an optical design program. The attained accuracy was approximately one-tenth of a wave.

The effects of alignment and surface figure errors and their compensation with each other in optical systems are analyzed based on computer simulations with exact ray tracing data. These effects are included in the prediction of system performance and the testing of optics. Several simple systems are used as examples. In the prediction of system performance, a Ritchey-Chretian telescope and a Reflaxicon system are studied. A correct alignment can be found to compensate certain surface figure errors in the system. This will allow larger surface figure errors to be tolerated in the system. In the testing of optics, a method to separate the figure errors from the alignment error contributions is discussed and an off-axis test configuration, the Ritchey-Common test, is studied thoroughly. A figure design approach is suggested and compared with other approaches for reduction of the measured wavefront data in the Ritchey-Common test.