The ability of periodic surface variations to influence and control the electromagnetic response of interfaces and structures has been recognised for many years. Concurrently with these investigations, it has been found that individual particles and wires support interesting electromagnetic resonances. It has also long been established that multi-layer structures of planar interfaces may also result in interesting electromagnetic responses. Multi-layer structures of alternating dielectrics have been shown to produce periodic transmission resonances, however, if one of the dielectrics is replaced with a thin metallic film, it has recently been demonstrated that wide band-pass regions are formed in the electromagnetic response of the structure. The work presented in this thesis can be considered to be separated into two distinct, but related, areas. One of the areas involves the analysis of wire grid arrays. It is demonstrated that, like the case of deep surface relief perturbations, the waveguide modes in the slits can be considered as the evolution of surface modes on shallow surface relief perturbations. The perturbation effects of the slits on the surface modes and the effect of their excitation on optically thick and thin wires are also investigated. Finally, a new electromagnetic resonance is presented on both 1-dimensional and 2-dimensional wire grid arrays. It is shown that this is closely related to the localised surface modes that have been shown to occur on individual particles and wires. However, the resonance presented is shown to be subtly different from these modes, which typically result in a transmission and reflection extinction, because the planar geometry of the wires and the periodicity result in a reflection enhancement, even when the wires are optically thin. The second area of this work may be separated into two distinct sub-sections. The first section examines the electromagnetic response of dielectric/metal multi-layer stacks. These are confirmed to exhibit a periodic series of broad band-pass regions, with the spectral location of these regions being dependent only on the unit cell, not the full extent of the structures. The location of each band-edge of these regions are then demonstrated to be a result of the matching of boundary conditions between standing waves in the cavities having either a cos or a sin standing wave function, and the evanescent fields inside the metal layers having either a sinh or a cosh field distribution. The second section examines the electromagnetic response of continuous surface relief gratings, with a rectangular cross-section, whose ridges are very thin. It is shown that vertical standing waves form, similar to the cavity waveguide modes, except with the fields coupled through the wires not across the grooves. These are then shown to reach a finite limit frequency as the grating height tends to infinity. Thus, the resonances have evolved into a different mode beyond a certain grating amplitude. This mode is shown to to be equivalent to the band-pass region described in multi-layer metal/dielectric stacks. However, scattering and periodicity considerations require that only the low frequency band-edge can be coupled to at normal incidence, while only the high frequency band-edge may be coupled to at grazing incidence.

The purpose of this study is to quantify patterns or trends of electromagnetic ducting conditions in the Arctic. On average, ducts occurred 5% of the time in the summer months, and 2-3% in the spring, fall, and winter months. This is considered a low approximation due to the vertical resolution of the sounding data. For some local regions, ducts occurred up to 20% of the time, especially in summer months. In general, local areas near coast lines or near the pole over ice/ocean had higher frequency of ducts than local areas over land mass. For summer and fall months, humidity gradients contributed most to the formation of a duct, while temperature gradients contributed to a lesser degree. For spring months, temperature gradients contributed most to the formation of the duct, while humidity gradients contributed to a lesser degree. For winter months, due to the extremely cold surface temperatures and low available humidity, temperature gradients were the dominant contribution to duct formation, and humidity gradients worked against duct formation.

The demand for high data rate communications and renewable energy sources has led to new materials and platforms for optoelectronic devices, which require nanometer scale feature sizes. Devices that operate in the visible and near-infrared commonly have active areas with dimensions on the order of the diffraction limit λ/2^n, where λ is the free space wavelength and n is the index of refraction, for which the ray optics modeling techniques and bulk focusing optics traditionally used in optoelectronic device design are no longer applicable. In this subwavelength regime, nanophotonic light-trapping strategies are required to localize electromagnetic fields in the active area. This dissertation details the application of nanophotonics to two optoelectronic systems: extrinsic photodetectors for silicon photonics and light-trapping in organic photovoltaics. Error-free reception of 10 Gb/s data at λ = 1.55 μm is demonstrated with a Si⁺ ion-implanted silicon waveguide photodiode. To mitigate the relatively small absorption coefficient of ion-implanted silicon, resonant cavity enhancement using in-line Fabry-Pérot and 1D photonic crystal cavities, as well as slow light enhancement using a coupled resonator optical waveguide are discussed. The extension of these photodiodes to the mid-infrared is demonstrated using Zn⁺ implantation to detect over a range of λ = 2.2-2.4 μm, and a new method for modulation and switching in integrated optics by using interference in a resonant cavity, termed coherent perfect loss (CPL), is presented. Finally, the upper limit of nanophotonic light trapping is derived for organic photovoltaics with material anisotropy included.

As recentes aplicações que utilizam bandas ultralargas e comunicação pulsada necessitam de antenas adaptadas às suas necessidades. Para tanto, é necessário entender melhor o funcionamento dessas antenas em toda a banda utilizada e sua resposta aos pulsos de entrada. Nesse sentido, algumas ferramentas de análise de antenas no domínio do tempo foram desenvolvidas e utilizadas de modo a explicar o mecanismo de radiação de algumas antenas. Através da utilização de estruturas grandes com relação à duração do pulso de entrada, é possível identificar como o pulso se propaga e é refletido pela estrutura. Em seguida, é estabelecida a relação entre a localização do pulso e a radiação gerada pela geometria da antena nessa posição. Com isso se pode identificar as origem das características da resposta impulsiva da antena e a sua relação com a aceleração de cargas que ocorre na estrutura. Finalmente, são apresentados alguns resultados relacionados ao desempenho da antena como dispersão, distorção e diagrama de radiação de energia normalizado. / The recent applications that uses UWB and pulse communications demands antennas that fits better its constraints. Therefore, it is necessary to understand the behaviour of these antennas in all the bandwidth used and its response to input pulses. With this objective, some analysis tools for antennas in the time domain have been developed. These tools provided and explanation to the radiation mechanism of some antennas. Through the use of large structures with respect to the duration of the input pulse it is possible to identify how the pulse propagates and how it is reflected by the structure. The relationship between the pulse position and the radiation of the antenna is then established for every position. This procedure enables the identification of the relationship between the antenna impulse response and the acceleration of charges in the structure. Finally, we present some results related to the performance of the antenna such as dispersion, distortion and normalized energy radiation pattern.

The focus of this thesis is the interaction of electromagnetic fields with chiral structures in the microwave regime. Through this study, which focuses on three regimes of electromagnetic interactions, I aim to develop a deeper understanding of the consequences and manifestations of chiral interactions The structures are on the order of, or smaller than, the wavelength of the probing radiation. As the structures are chiral, they have broken inversion symmetry, and exist in two states where one is the mirror image of the other. The results in this thesis can have impacts on future optical communications technologies and methods of sensing biological molecules. To begin with, the manipulation of the circular polarisation of a propagating beam by bilayer chiral metasurfaces is investigated. The metasurfaces consist of two layers of stacked crosses with a twist between top and bottom layers, forming chiral metamolecules. A broad frequency region of dispersionless polarisation rotation appears between two resonances, due to alignment between electric and magnetic dipoles. The dependence of this effect on the layer separation is studied for two similar metasurfaces. Evanescent chiral electromagnetic fields are the focus of the next chapter. An array of chiral antennas produces chiral near-fields at their resonant frequency. Aligned and subwavelength helices placed within this field interact differently depending on the handedness of the field with respect to the handedness of the helices. This difference in interaction strength is measured for the helices and an effective medium model where multipolar interactions are forbidden. Comparison of these two systems leads to the conclusion that the contribution to a chiral interaction from multipolar modes is minimal, in contrast to previous publications. The third study concentrates on the electromagnetic wave bound to an "infinitely long" metal helix. The helix has infinite-fold screw symmetry, and this leads to interesting features in the energy-dispersion of the waves it supports. The broad frequency range of high, tunable, dispersionless index is interpreted using a geometrical approach, and the factors that limit the bandwidth explained. A modified geometry is suggested for increased bandwidth. The final part of the thesis is dedicated to future work, based on the results presented thus far. Three suggestions for future study are presented, including chiroptical signals from higher-order chiral arrangements, the effect of reflecting surfaces next to chiral objects and the possible use of orbital angular momentum for chiroptical measurements.

As recentes aplicações que utilizam bandas ultralargas e comunicação pulsada necessitam de antenas adaptadas às suas necessidades. Para tanto, é necessário entender melhor o funcionamento dessas antenas em toda a banda utilizada e sua resposta aos pulsos de entrada. Nesse sentido, algumas ferramentas de análise de antenas no domínio do tempo foram desenvolvidas e utilizadas de modo a explicar o mecanismo de radiação de algumas antenas. Através da utilização de estruturas grandes com relação à duração do pulso de entrada, é possível identificar como o pulso se propaga e é refletido pela estrutura. Em seguida, é estabelecida a relação entre a localização do pulso e a radiação gerada pela geometria da antena nessa posição. Com isso se pode identificar as origem das características da resposta impulsiva da antena e a sua relação com a aceleração de cargas que ocorre na estrutura. Finalmente, são apresentados alguns resultados relacionados ao desempenho da antena como dispersão, distorção e diagrama de radiação de energia normalizado. / The recent applications that uses UWB and pulse communications demands antennas that fits better its constraints. Therefore, it is necessary to understand the behaviour of these antennas in all the bandwidth used and its response to input pulses. With this objective, some analysis tools for antennas in the time domain have been developed. These tools provided and explanation to the radiation mechanism of some antennas. Through the use of large structures with respect to the duration of the input pulse it is possible to identify how the pulse propagates and how it is reflected by the structure. The relationship between the pulse position and the radiation of the antenna is then established for every position. This procedure enables the identification of the relationship between the antenna impulse response and the acceleration of charges in the structure. Finally, we present some results related to the performance of the antenna such as dispersion, distortion and normalized energy radiation pattern.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy / The work presented in this thesis extends and contributes to research in the field of lightning injury mechanisms. Six mechanisms have been described in the literature about lightning injury. This thesis takes an in-depth look at the sixth injury mechanism. The sixth mechanism may be thought of as a ‘pressure-shock wave’ which is directly proportional to the current of the lightning discharge, and which is present immediately surrounding lightning’s luminous channel. A literature review, case studies and two novel experiments helped confirm the sixth mechanism’s existence. The medical data and the lightning data were then aligned. Two main questions were addressed, namely within what range is a human at risk; and what is the risk of lightning’s pressure shock wave. This ‘pressure-shock wave’ may explain some of the more curious lightning injury patterns seen on lightning-strike victims. Knowledge and insight into the sixth mechanism may have direct and indirect applications to those working in the fields of lightning injury and lightning protection. This thesis represents a contribution to the literature in both medicine and engineering.

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Abstract not available

The propagation of electromagnetic waves through media with dispersive dielectric permittivity. It is shown that under resonant conditions the energy velocity is always subluminal. The energy velocity is different from the group velocity and the delay velocity. The momentum conservation equation with the Lorentz force is derived from macroscopic and microscopic analysis. The relations of the forces on the dielectric with momentum and pseudomomentum of the electromagnetic field are clarified.