Abstract It has been reported that as much as 12% of global electricity production goes into producing artificial light using arc discharge lamps and that global annual production of these lamps may be as much as 1.2 billion units. In the liquid steel production industry, one metric tone of steel demands, on average, 400 kW-hr and in the year 2007, the crude steel output reached 1,343.5 million metric tons. In both instances, engineered electric arcs are present and represent major loads in electrical power systems which require the utmost attention. They observe a highly non-linear behaviour with the capacity to export harmonic distortion and flicker into the power system. Electric arc furnace installations, in particular, are well-known to be sources of dynamic disturbances affecting neighbouring loads. Arc discharge lamps, on aggregate, may exhibit the same perturbing effect. Over the years, the non-linear nature of these loads and their ubiquitous nature have caught the interest of researchers in all corners of the world and from different backgrounds, including this author. The research work reported in this thesis advances current knowledge in the modelling and simulation of electric arcs with particular reference to arc discharge lamps with electromagnetic ballasts and electric arc furnaces with particular reference to operational unbalances and the impact in the installation of ancillary power electronics equipment. In these two quite distinct applications, linked by the presence of engineered electric arcs, the fundamental modelling item is a non-linear differential equation which encapsulates the physic of the electric arc by applying power balance principles. The non-linear differential equation uses the arc conductance as state variable and adapts well to model a wide range of characteristics for which a set of experimental coefficients are available. A fact of perhaps equal relevance is that the non-linear differential equation is amenable to algebraic representations using operational matrices and suitable for carrying out periodic steady-state solutions of electric circuits and systems. The modelling and numerical solution takes place in the harmonic space where all harmonics and cross-couplings between harmonics are explicitly represented. Good application examples are the harmonic domain solution of arc discharge lamps with electromagnetic ballasts and the harmonic domain solution of electric arc furnaces with ancillary power electronics equipment. Building on the experience gained with the representation of the arc discharge lamps with electromagnetic ballasts, the research turns to the representation of the electric arc furnace installation with provisions for reactive power compensation using power electronic control and harmonic filters. This is a three-phase application which comprises several nodes, giving rise a large-scale model of a non-linear system which is solved in the direct frequency domain using a blend of the Newton-Raphson method and the Gauss-Seidel method, achieving robust iterative solution to a very tight tolerance. Both algorithms are implemented in MATLAB code and the raw simulation results which are the harmonic complex conjugated vectors of nodal voltages are used to assess in a rather comprehensive manner the harmonic interactions involved in both kinds of applications.

The growing variability of electrical characteristics is a major issue associated with continuous downscaling of contemporary bulk MOSFETs. In addition, the operating conditions brought about by these same scaling trends have pushed MOSFET degradation mechanisms such as Bias Temperature Instability (BTI) to the forefront as a critical reliability threat. This thesis investigates the impact of this ageing phenomena, in conjunction with device variability, on key MOSFET electrical parameters. A three-dimensional drift-diffusion approximation is adopted as the simulation approach in this work, with random dopant fluctuations—the dominant source of statistical variability—included in the simulations. The testbed device is a realistic 35 nm physical gate length n-channel conventional bulk MOSFET. 1000 microscopically different implementations of the transistor are simulated and subjected to charge-trapping at the oxide interface. The statistical simulations reveal relatively rare but very large threshold voltage shifts, with magnitudes over 3 times than that predicted by the conventional theoretical approach. The physical origin of this effect is investigated in terms of the electrostatic influences of the random dopants and trapped charges on the channel electron concentration. Simulations with progressively increased trapped charge densities—emulating the characteristic condition of BTI degradation—result in further variability of the threshold voltage distribution. Weak correlations of the order of 10-2 are found between the pre-degradation threshold voltage and post-degradation threshold voltage shift distributions. The importance of accounting for random dopant fluctuations in the simulations is emphasised in order to obtain qualitative agreement between simulation results and published experimental measurements. Finally, the information gained from these device-level physical simulations is integrated into statistical compact models, making the information available to circuit designers.

This thesis introduces the reader to the near-field baseband pulse radio communication for biomedical implants. It details the design and implementation of the complete communication system with a particular emphasis on the antenna structure and waveform coding that is compatible with this particular technology. The wireless communication system has great employability in small pill-sized biomedical diagnostic devices offering the advantages of low power consumption and easy integration with SoC and lab-in-a-pill technologies. The greatest challenge was the choice of antenna that had to be made to effectively transmit the pulses. A systematic approach has been carried out in arriving at the most suitable antenna for efficient emanation of pulses and the fields around it are analysed electromagnetically using a commercially available software. A magnetic antenna can be used to transmit the information from inside a human body to the outside world. The performance of the above antenna was evaluated in a salt solution of different concentrations which is similar to a highly conductive lossy medium like a human body. Near-field baseband pulse transmission is a waveform transmission scheme wherein the pulse shape is crucial for decoding information at the receiver. This demands a new approach to the antenna design, both at the transmitter and the receiver. The antenna had to be analysed in the time-domain to know its effects on the pulse and an expression for the antenna bandwidth has been proposed in this thesis. The receiving antenna should be able to detect very short pulses and while doing so has to also maintain the pulse shape with minimal distortion. Different loading congurations were explored to determine the most feasible one for receiving very short pulses. Return-to-zero (RZ), Non-return-zero (NRZ) and Manchester coded pulse waveforms were tested for their compatibility and performance with the near-field baseband pulse radio communication. It was concluded that Manchester coded waveform are perfectly suited for this particular near-field communication technology. Pulse interval modulation was also investigated and the findings suggested that it was easier to implement and had a high throughput rate too. A simple receiver algorithm has been suggested and practically tested on a digital signal processor. There is further scope for research to develop complex signal processing algorithms at the receiver.

The objective of the work of this thesis is to design, fabricate, and characterise high performance micromachined antennas with fixed and reconfigurable bandwidth. The developed integrated antennas are suitable for MMICs integration at millimetre wave frequencies (G-band) on MMICs technology substrates (i.e GaAs, Si, InP). This work is done through a review of the scientific literature on the subject, and the design, simulation, fabrication and experimental verification, of various suitable designs of antenna. The novel design of the antennas in this work is based on elevated antenna structures in which the radiator is physically micromachined above the substrate. The antenna design schemes offer a suitable method to integrate an antenna with other MMICs. Further, this method eliminates undesired substrate effects, which degrades the antenna performance drastically. Also in this work we have for the first time realized different micromachined antenna topologies with different novel feeding mechanisms - offering more degrees of freedom for antenna design and enhancing the antenna performance. Experimental and simulation results are provided to demonstrate the effectiveness of the proposed antenna designs and topologies in this work. A new approach for fabricating printed antennas is introduced in this work to fulfil the fabrication process requirements. It provides a new method for the fabrication of 3-D multilevel structures with variable heights, without etching the substrate. Further, the height of the elevated structures can be specified in the process and can vary by several microns, regardless of the substrate used. This can be used to further enhance the bandwidth and gain of the antenna - avoiding substrate thinning and via holes, and increasing the fabrication yield. Thus, the elevated antenna can meet different application requirements and can be utilized as a substrate independent solution. In this work we have introduced the concept of reconfigurable antennas at millimetre wave band. Also, we have investigated various aspects associated with lowering the pull-down voltage and overcoming the stiction problem of MEMS switches required for the proposed reconfigurable antennas. This was achieved by developing MEMS technology which can be integrated with MMICs fabrication process. Two novel reconfigurable elevated patch antenna topologies were designed to demonstrate the developed technology and their performances were discussed. The result we obtained from this work demonstrates the feasibility of MEMS reconfigurable printed antennas at G-band frequencies. This will open a new field in MMICs technology and increasing system integration capabilities and functionality. The devolved technology in this thesis could be utilized in many unique applications including short range high data rate communication systems and high-resolution passive and active millimetre-wave imaging.

The work presented in this thesis describes some theoretical and experimental aspects of the relationships between electromagnetic fields and a non-contact type of eddy current gauge, which utilises a cylindrical solenoid and coaxially positioned metallic bar, either ferrous or non-ferrous. A rigorous mathematical analysis of the eddy current gauging system is presented, together with an evaluation of the solutions produced. This rigorous mathematical treatment is simplified, and the mathematical model thus produced is verified experimentally. The simplified mathematical model is used as a basis for a practical eddy current gauge operating at a frequency of 10 kHz, using ferrous or non-ferrous metal. A novel technique is then described in which the simplified mathematical model is used as part of a practical microprocessor-aided eddy current gauging system, which allows appropriate compensation to be introduced into the system for ferrous metallic conductors with magneticflaws present. This system uses a type of magnetic saturation technique.

Thin film solar cells with a band gap graded in the thickness direction were prepared by vacuum evaporation of various alloys of Cadmium Sulphide (CdS) and Cadmium Telluride (CdTe) onto glass substrates. Theoretical computer analyses were carried out and show that a solar cell with a graded band gap surface layer ought to be a more efficient photovoltaic converter than a conventional homojunction device. A vacuum evaporator capable of multiple simultaneous co-evaporations was built and used initially to deposit only the CdS and CdTe films and subsequently mixed and graded films of Cadmium Sulphide Telluride (CdS x Te 1-x). The composition of the mixed and graded films was controlled by a set of shutters built above the sources, rather than by the control of the temperature of the sources. The electronic properties of the films were adjusted by co-evaporation of dopant materials such as Cadmium (Cd), Indium (In) and Copper (Cu), and measured by Hall Effect measurements. The physical properties of the films such as the band gap, crystal phase and grain size were investigated by optical transmission measurements, X-ray analysis and scanning electron microscopy respectively. Finally, p-n junctions with n-type graded band gap surface layers on top of either pure p-type CdTe films or mixed p-type CdS0.5Te0.5 films were prepared. However, the photoresponse of these structures was low, probably due to very short minority carrier life-times, lack of low resistance contacts and cross diffusion of dopant materials. Nevertheless, the characteristics of individual materials and the spectral response of the devices indicated that if these problems could be solved, a successful solar cell could be made.

This thesis presents work on the development of a number of scanned electrochemical probe microscopies. Such techniques have widespread applications, from materials science to the life sciences. Advances in flexible instrumentation, coupled with the theoretical description of electrochemical systems, are central themes which allowed for the fruitful investigation of a variety of experimental systems. Theoretical descriptions of scanning ion conductance microscopy (SICM) were developed, particularly to investigate the effect of tip-geometry on imaging resolution. This technique has already found a number of applications in the life sciences, but image resolution has not previously been addressed adequately. Images were recorded showing tip-convolution that were in agreement with theoretical predictions. The scanning microcapillary contact method (SMCM) was developed, as a method of assessing spatial heterogeneities in electrode activity on the submicron length-scale. An electrolyte filled microcapillary containing a reference/auxiliary electrode was approached to a substrate (working) electrode surface, via piezoelectric positioners. Contact of the electrolyte meniscus with the substrate electrode was sensed by a current flowing. Electrochemical measurements were performed before the microcapillary was retracted and another point on the sample was characterised. Spatial heterogeneities in electrode activity were imaged on a sub-micron length-scale and the activity of basal plane highly oriented pyrolytic graphite (HOPG) was demonstrated. Tip position modulation scanning electrochemical microscopy (SECM-TPM), where an ultramicroelectrode (UME) is oscillated perpendicularly to a surface and an amperometric current is recorded, was investigated experimentally and theoretically. A model including convective mass-transport was developed that gave an accurate description of the experimental situation. It was demonstrated that SECM-TPM is a potentially powerful approach for the measurement of the permeability of a sample. SECM experiments were performed investigating the growth of Ag particles at a liquid/liquid interface, which was caused through the electrodissolution of a Ag UME in an aqueous phase, and the reduction of the Ag+ ion by an electron donor in the organic phase. A model was created that allowed for the interpretation of data. Cyclic voltammetry investigations of HOPG covered with a Nafion film containing a redox mediator confirmed the activity of basal plane HOPG, as demonstrated by SMCM measurements. Nafion slowed diffusion sufficiently to allow the spatial-decoupling of surface sites with different activity.

This thesis details an investigation into the application of genetic algorithms to indoor optical wireless communication systems. The principle aims are to show how it is possible for a genetic algorithm to control the received power distribution within multiple dynamic environments, such that a single receiver design can be employed lowering system costs. This kind of approach is not typical within the research currently being undertaken, where normally, the emphasis on system performance has always been linked with improvements to the receiver design. Within this thesis, a custom built simulator has been developed with the ability to determine the channel characteristics at all locations with the system deployment environment, for multiple configurations including user movement and user alignment variability. Based on these results an investigation began into the structure of the genetic algorithm, testing 192 different ones in total. After evaluation of each one of the algorithms and their performance merits, 2 genetic algorithms remained and are proposed for use. These 2 algorithms were shown capable of reducing the receiver power deviation by up to 26%, and forming, whilst the user perturbs the channel, through movement and variable alignment, a consistent power distribution to within 12% of the optimised case. The final part of the work, extends the use of the genetic algorithm to not only try to optimise the received power deviation, but also the received signal to noise ratio deviation. It was shown that the genetic algorithm is capable of reducing the deviation by around 12% in an empty environment and maintain this optimised case to within 10% when the user perturbs the channel.

High-speed wireless optical communication links have become more popular for personal mobile applications. This is a consequence of the increasing demand from the personal information service boom. Compared to the radio frequency domain, optical wireless communication offers much higher speeds and bit rates per unit power consumption. As stated by the official infrared standard IrDA optical communication enjoys much lower power consumption than Bluetooth, with an inherent security feature while in Line of Sight (LOS) applications. There are also drawbacks such as the infrared radiation cannot penetrate walls as radio frequencies do and interference from the background contribute to the channel dispersions. Focus on the modulation aspects of the optical wireless communication, this thesis try to improve the channel immunity by utilising optimised modulation to the channel. Modulation schemes such as on off keying (OOK), pulse amplitude modulation (PAM) and pulse position modulation (PPM) and pulse position and amplitude modulation PAPM schemes have been validated. The combined power and bandwidth requirements suggest that the adaptive modulation schemes can provide reliability when deployed in a real time channel, resulting in improved system performance. As a result, an adaptive modulation technique is proposed. Extensive simulations of severe noise distraction have been carried out to validate the new scheme. The simulation results indicate that the new scheme can provide increased immunity against channel noise fluctuation at a relatively low complexity. The scheme obtained formed a basis to support reliable mobile optical wireless communication applications. The adaptive scheme also takes the real time channel conditions into account, which is different from existing schemes. Guaranteed system performance can be secured without compromising power and bandwidth efficiency. This is also a new approach to realise reliable optical wireless links. Fuzzy logic control module has been developed to match the adaptive pattern.

The research presented in this Thesis investigates the strategic behaviour of generating firms in bid-based electricity pool markets and the effects of control methods and network features on the electricity market outcome by utilising the AC network model to represent the electric grid. A market equilibrium algorithm has been implemented to represent the bi-level market problem for social welfare maximization from the system operator and utility assets optimisation from the strategic market participants, based on the primal-dual interior point method. The strategic interactions in the market are modelled using supply function equilibrium theory and the optimum strategies are determined by parameterization of the marginal cost functions of the generating units. The AC power network model explicitly represents the active and reactive power flows and various network components and control functions. The market analysis examines the relation between market power and AC networks, while the different parameterization methods for the supply function bids are also investigated. The first part of the market analysis focuses on the effects of particular characteristics of the AC network on the interactions between the strategic generating firms, which directly affect the electricity market outcome. In particular, the examined topics include the impact of transformer tap-ratio control, reactive power control, different locations for a new entry’s generating unit in the system, and introduction of photovoltaic solar power production in the pool market by considering its dependencyon the applied solar irradiance. The observations on the numerical results have shown that their impact on the market is significant and the employment of AC network representation is required for reliable market outcome predictions and for a better understanding of the strategic behaviour as it depends on the topology of the system. The analysis that examines the supply function parameterizations has shown that the resulting market solutions from the different parameterization methods can be very similar or differ substantially, depending on the presence and level of network congestion and on the size and complexity of the examined system. Furthermore, the convergence performance of the implemented market algorithm has been examined and proven to exhibit superior computational efficiency, being able to provide market solutions for large complex AC systems with multiple asymmetric firms, providing the opportunity for applications on practical electricity markets.