Thesis (Ph. D.)--University of Wisconsin--Madison, 1974. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (MScEng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

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M.Ing. / The heating and drying of products is a process which is essential to improve the quality. This process has been around since the beginning of the industrial age. Most industries use natural energy sources, e.g. coal, to generate the energy that is needed. This energy is then used to heat air and this in turn is used to dry the products. Heat transfer is used to dry the materials and it is a known fact that this mechanism is not effective due to huge losses. A certain company identified this problem and decided to investigate microwave energy as an alternative energy source. The aim of the project was to determine if microwave energy could dry the phosphate and to do an economic feasibility study on such a microwave oven. The operation of microwave sources was examined and the magnetron was found to be the most effective source. Magnetrons that operate at a frequency of 2.45GHz, are easily obtainable and therefore also more economical than magnetrons that operate at other frequencies. The loss mechanisms that are associated with microwave heating as well as the parameters associated with volumetric heating were then investigated. It was found that the complex permittivity and permeability of the material to be heated, are important properties associated with microwave heating and these were not known and needed to be determined. After examlnlng several methods to determine these properties, the measurements were done by means of a network analyser. From the results it was evident that the phosphate losses were relatively high enabling most of the microwave energy to be absorbed. These results were confirmed after further tests were done.

This thesis discusses both qualitative and quantitative characteristics of the horizontal electromagnetic field produced by the flow of eddy currents in a conductor. The exciting field is supplied by a large horizontal loop carrying an alternating current, and the secondary horizontal field is measured by detecting the voltage induced in a small vertical search coil in the plane of the loop. Determinations of both the ratio of the horizontal field to the vertical, and the phase angle between them are made at various points along a diameter directly above the centre line of each conductor. Corrections to eliminate extraneous voltages induced in all parts of the measuring apparatus are applied to these measurements. The corrected values are then plotted as profiles of relative amplitude and phase for several positions of each conductor. The shapes of these curves and possible mathematical expressions relating them to the physical dimensions and position of the conductor are discussed, and some approximations of the configuration of surface current flow are suggested. The present results are compared with those obtained by previous experimenters and certain changes of fundamental concepts are suggested. Possible application of these results to qualitative interpretation of measurements taken over actual ore-bodies, and methods of accurate determination of size and depth of the bodies are proposed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

It is assumed that charged, spin-½, matter distributions can be described in terms of a Dirac spinor field interacting with the electromagnetic field and a scalar gravitational field. The field equations and the energy-momentum tensor are found from an action principle. The fields are not quantized. The field equations are examined and various limiting forms discussed. This thesis deals particularly with the time-independent spherically-symmetric case. Solutions are found for the exterior region of a charged gravitating sphere. The behaviour of these solutions depend on the value of the charge-mass ratio. When this ratio has the value (4πG)½, where G is the gravitational constant, the entire system can be solved analytically. The ensuing solution, called the Weyl-Majumdar solution, is obtained and discussed. When the charge-mass ratio is smaller than (4πG)½, normalised solutions are found which yield electrostatic and gravitational potentials singular at the origin. The matter density is well-behaved everywhere. Normalised solutions were not found for larger charge-mass ratios. The significance of the solutions, and the accuracy of the numerical technique are discussed. Alternative Lagrangian densities are considered which may yield non-singular solutions. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A study of the hyperbolic electrostatic electron mirror is presented. The focal properties of the mirror are determined both theoretically and experimentally. In the theoretical study the mirror field is formed between a positive hyperbolic potential surface and the negative asymptotic cone of half angle arctan 1:2 [square root of 2]. The focal properties are obtained from the solutions of the equations for the radial and axial motions of the electron in the mirror field. The analysis includes the effect of an axial aperture (for entrance and exit of electrons) in the positive surface. The paraxial values of focal length arid focal distance and their second order spherical aberrations are calculated by expanding the expressions for the focal properties in terms of the incident radial height. The mirror field in the experimental study is formed between a similar negative electrode and a flat apertured positive electrode. The experimental values of the focal properties are determined by a ray tracing method in which the pattern of shadows cast by a grid in the incident and reflected beams is analyzed. Comparison of the experimentally measured and the theoretically calculated focal properties shows satisfactory agreement. The mirror exhibits over-corrected spherical aberration in certain ranges of its operation which suggests its use to improve the resolution limit of electron optical devices.

In this work, we present rigorous and efficient methods for analyzing scattering from the following structures • Tandem Slit loaded with homogeneous material • Eccentrically loaded cylinder with multiple slits • Semicircular cylinder and slit • Dielectric loaded Wedge shaped cylinder • Circular cylinder with resonant cavities and resonant cavities on circular arc. For analyzing the material loaded tandem slit configuration, the boundary value problem is formulated into a pair of simultaneous Wiener-Hopf equations via Fourier transformation. After decoupling these equations by elementary transformation, each modified Wiener-Hopf equation is reduced to a Fredholm integral equation of the second kind. The integral equations are then solved approximately to yield the Fourier transform of the diffracted fields. The inverse transform is evaluated asymptotically to obtain the far field expressions. Measurements and numerical simulations are also performed for several different geometric and material configurations. The analytic solutions compare well with measured and simulated results. The possibility of reducing beamwidth and increasing power coupled through the loaded tandem slit is explored. The analysis of the eccentrically loaded cylindrical cavity with multiple slits under plane wave illumination is formulated using two distinct approaches: (1) an integral equation/combined boundary condition (IE/CBC) formulation and (2) an integral equation/Neumann series expansion (IE/NS) formulation. The IE/NS formulation is shown to converge faster than the IE/CBC formulation based on the proper edge behavior exhibited by the Neumann series current expansion functions. Results for the backscattered radar cross section (RCS) of several geometries are presented, and the relationships between the RCS and the scatterer characteristics are explored. The applicability of the Neumann series method to find a fast method for evaluating scattering from a metallic strip and semicircular cylinder is presented. The Neumann series of different periodicity is used for studying scattering from wedge shaped cylinder. The Neumann series is also applied to study scattering from a circular cylinder with resonant cavities and resonant cavities on a circular arc. These resonant cavities on a circular arc have superdirective properties, which are useful for high gain antenna design.

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