This thesis is concerned with the interaction of an optical wave with a microwave in a waveguiding structure coupled by a second order nonlinearity. Emphasis is laid upon the generation of ultrashort electrical transients via optical rectification (OR) as well as cascading effects due to the interplay of OR and the linear electro-optic effect. A simple transmission line model is introduced to explain qualitatively the basic physical mechanisms of an externally induced polarisation in a travelling wave structure. For a quantitative description, evolution equations for the overall interaction between the microwave and the optical wave based on a coupled mode formalism are developed. The basic properties of the structure under consideration are discussion and techniques for their evaluation are introduced. A set of corresponding parameters for typical structures is estimated and used for calculations throughout the thesis. The generation of electrical signals from optical waves via OR is discussed in detail for the cases of single and mixed polarization optical modes in the structure. The self phase modulation due to cascading of OR and the electro-optic effect is elucidated. It is shown that continuous wave solutions of the conservative system are modulationally unstable in a large range of relevant system parameters. The possibility of formation of solitary waves due to the mutual interaction of optical wave and microwave is considered in the context of long wave short wave interaction. Basic properties of bright stationary solutions and their excitation are discussed. The possibility of formation of solitons due to microwave self-interaction is illuminated. The linear stability of bright solitary waves is investigated. The observed oscillations and radiation of perturbed propagated bound states are explained by the existence of discrete, quasi-bond internal modes of the stationary solutions. Collision scenarios are addressed.

A systematic investigation of the electrochemical behaviour of two sets of microelectrode arrays, fabricated by standard photolithographic and reactive-ion etching techniques, is presented. The first set of microelectrode arrays had a constant relative centre-centre spacing of 10r (where r is the electrode radius). As a value of r was decreased, the cyclic voltammograms recorded from the array became increasingly peak-shaped, due to merging of the diffusion fields of the individual electrodes. Furthermore, it was shown that the peak current densities obtained were largest for the arrays with the smallest individual electrodes, as were the signal-to-noise ratios (SNRs). Electroplating the individuals electrodes with platinum black was also shown to increase the peak currents and the SNRs, due to an increase in the effective surface area. Sigmoidal voltammograms, which are indicative of radial diffusion, were obtained for an individual electrode radius of 25 mm but not for arrays with smaller electrodes. To obtain radial diffusion for an array of 2.5 mm electrodes, it was shown (using a second set of microelectrode arrays) that a minimum relative centre-centre spacing of 40r is required. Further enhancement of the peak current densities were obtained by decreasing the size of the individual electrodes. A series of nanoelectrode arrays were fabricated using electron-beam lithography (EBL). The voltammograms obtained from these arrays exhibited a continual increase in the recorded peak current as the individual electrodes radius was decreased to a value of 110 nm. Since EBL is a slow and costly technique, nanoimprint lithography (NIL) was investigated as an alternative method of fabricating nanoelectrode arrays and comparable results were obtained from arrays produced by EBL and NIL. A dissolved oxygen and temperature sensor incorporating a working microelectrode array was also designed and fabricated. The sector comprised a densely packed array of 2.5 mm radius electrodes and a micro-reference electrode, both of which were covered with an agarose electrolyte gel enclosed in an SU8 chamber. A thermal resistor was included for temperature compensation of the dissolved oxygen measurements. The Ag|AgCl micro-reference electrode was found to be stable for approximately 80 hours in 0.1 M KCl, with 100 nA of current passing through it. Linear calibration curves were obtained from both temperature and dissolved oxygen measurements

Drift-Diffusion, Hydrodynamic and Monte Carlo simulations have been used in this work to simulate strained Si/SiGe devices for RF and CMOS applications. For numerical simulations of Si/SiGe devices, strain effects on the band structure of Si have been analyzed and analytical expressions are presented for parameters related to the bandgap and band alignment of Si/SiGe heterostructure. Optimization of n-type buried strained Si channel Si/SiGe MODFETs has been carried out in order to achieve high RF performance and high linearity. The impact of both lateral and vertical device geometries and different doping strategies has been investigated. The impact of the Ge content of the SiGe buffer on the performance of p-type surface channel strained Si/SiGe MOSFETs has been studied. Hydrodynamic device simulations have been used to assess the device performance of p-type strained Si/SiGe MOSFETs down to 35 nm gate lengths. Well-tempered strained Si MOSFETs with halo implants around the source/drain regions have been simulated and compared with those devices possessing only a single retrograde channel doping. The calibrations in respect of sub-100 nm Si and strained Si MOSFETs fabricated by IBM lead to a scaling study of those devices at 65 nm, 45 nm and 35 nm gate lengths. Using Drift-Diffusion simulations, ring oscillator circuit behaviour has been evaluated. Strained Si on insulator (SSOI) circuits have also been simulated and compared with strained Si circuits, Si circuits employing conventional surface channel MOSFETs along with SOI devices. Ensemble Monte Carlo simulations have been used to evaluate the device performance of n-type strained Si MOSFETs. A non-perturbative interface roughness scattering model has been used and validated by calibrating with respect to experimental mobility behaviour and device characteristics. The impact of interface roughness on the performance enhancement of strained Si MOSFETs has been investigated and evidence for reduced interface roughness scattering is presented, i.e., a smoother interface is suggested in strained Si MOSFETs. A 35 nm gate length Toshiba Si MOSFET has been simulated and the performance enhancement of 35 nm strained Si MOSFETs over the Toshiba Si device is predicted. Monte Carlo simulations are also employed to investigate the performance degradation due to soft-optical phonon scattering, which arises with the introduction of high-K gate dielectrics. Based on the device structures of the calibrated sub-100 nm n-type conventional and strained Si IBM MOSFETs, significant current degradation has been observed in devices with high-K gate dielectrics, HfO2 and Al2O3.

No description available.

The Lagrangian perturbation method for the NLS is revisited in the form of an equivalent direct problem. The analogy can be extended to arbitrarily perturbed systems. It is then possible to provide first order perturbation expansions for the fundamental soliton. The case of the damped NLS is considered and shown to fully comply with IST predictions. Subsequently the problem of NLS initial condition not corresponding to an exact soliton is examined. There are two issues that need to be considered: the location of the soliton solution and the modelling of the continuum. The location of the soliton solution is handled by considering the integrals of motion of the NLS. The improvement arises by the inclusion of the contributions due to the continuum. The results are compared with numerical calculations and are proved to be satisfactory provided that the initial pulse shape does not depart greatly from the Asech(z) functional form. The propagation problem is handled by considering the evolution of the soliton and the continuum separately and recombining them at the required time. Two cases are considered: the far field pattern and the position where the peak of the soliton lies. For the former the recombination of continuum with the soliton is achieved with the help of the inverse part of the IST. For the peak position a Bäcklund transform is considered. Results from both regimes are compared with numerical results and shown to agree satisfactorily.

Electricity usage has grown steadily ever since the first commercial generator came into operation more than one century ago. Power transmission networks too, have grown in size and in operational complexity to be able to handle the large blocks of electricity that travel from generator to consumers round-the-clock and with huge variations. At various stages of the development, state-of-the-art equipment, methods and techniques have been incorporated in the vast array of tools that power systems engineers have at their disposal to keep up with the demands imposed by the planning, management, operation and control of modern power systems. Transient stability has always been an issue of paramount importance in power system planning and operation. Arguably, most of the ideas and concepts associated with power system stability analysis were conceived many years ago. Nonetheless, continuous expansion of the network and the emergence of a new generation of fast acting, multi-purpose power system controllers have called for renewed research efforts in this all-important application area of power systems. In particular, there is growing concern that the power network is becoming more unbalanced, owing to higher operating voltages and a relentless drive for interconnection, and that unbalances may impair the effectiveness of power electronic-based loads and controllers. These are issues that may be difficult to address satisfactorily with conventional transient stability modelling approaches since they are based on the premise that the transmission network observes a perfect balance, even under faulted operating regimes. The study of a limited range of asymmetrical transient stability problems using conventional methods can be achieved, but only with great difficulty, which involves transforming the network into fictitious components (i. e. symmetrical components). This is significant since asymmetrical short-circuit faults constitute the largest percentage of faults that occur in the power network, and network designs based solely on the three-phase short-circuit-to-ground faults result in underengineered networks. Equally important issues are the widespread commissioning of modern power electronics controllers and the lack of suitable models and methods for assessing the impact of such controllers in network-wide operation with particular reference to transient stability and unbalanced operation. The research reported in this thesis addresses these issues and develops a direct time phasedomain model for conducting multimachine transient stability analysis where asymmetrical operating conditions and the impact of modem power electronics controllers are represented. In this simulation environment, AC synchronous and asynchronous generators are represented together with asynchronous motors. The set of non-linear equations describing the machines are solved using discretisation and the trapezoidal rule of integration. The proposed model is compared against an industry standard power system package for cases of symmetrical operation. The generality and versatility of the model is demonstrated when applied to the analysis of symmetrical and asymmetrical power system operations. An important aspect of this research is a drive towards the solution of transient stability in real-time, where the results produced are in actual world time. This is achieved by embedding the model into a commercially available multi-purpose real-time station. To this end, coherency-based synchronous generators equivalent has been developed to enable the solution of multimachine systems in real-time. The equivalent unit is obtained based on the aggregation of the coherent generators using phase-domain techniques. Dynamic loads in the form of asynchronous motors are implemented within the multimachine network. The adverse influences of motor operation on voltage problems in the network under symmetrical and asymmetrical conditions are analysed. Transient analysis of dispersed generation is also considered where the asynchronous machine is operated as a generator alongside synchronous generators. The behaviours of the two type of generators under various networks and operating conditions are presented. Models of power electronics controllers in the direct time phase-domain are also described in this thesis. The generalised models of the Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM), Dynamic Voltage Restorer (DVR) and High Voltage Direct Current-Voltage Source Converter (HVDC-VSC) station are proposed. The SVC comprised of a fix capacitor and a thyristor controlled reactor (TCR) is developed. Here, switching functions are used to represent the operation of the thyristor. Models of STATCOM, DVR and HVDC-VSC station are developed based on the self-commutated voltage source converter (VSC) technology. The VSC is represented by the switching functions of its pulse width modulation (PWM) control, hence, providing a flexible model within the direct time phase-domain approach. The model of the VSC is implemented into the respective power electronics controllers enabling a convenient modular approach to be adopted. The power electronics controllers are incorporated into the multimachine environment for the analysis of transient and power quality related issues.

The thesis describes a new technique, called the flux-MMF diagram technique, for analysis and comparative evaluation of electrical machines. The technique has evolved from the principle of virtual work, and the -i diagram, used commonly in designing switched reluctance machines and relays. Several applications of this technique are demonstrated in the thesis, supported by experimental validation. These are, the prediction of electromagnetic and cogging torque ripple, modelling of the effect of skew on torque and torque ripple, modelling of the variation of torque constant due to saturation, and comparative evaluation of different types of electrical machines. The thesis shows that the technique can be applied successfully in analysis of a wide variety of electrical machines. These include conventional machines such as the DC commutator, PM brushless AC, Interior PM, and the synchronous reluctance machine; as well as non-conventional machines such as the switched reluctance, PM brushless DC, and the doubly-salient PM machine. The technique has been implemented in a finite-element software, with the help of a link program which links the FE software with the dimensioning or sizing software, such as PC-BDC, produced by the SPEED Laboratory. The link program serves as a vital means of shortening the time it takes to analyse a new design in an FE software, by several orders of magnitude. The thesis also describes a new brushless doubly-salient permanent-magnet machine, called the flux-reversal machine. The design and fabrication process, and the experimental results are presented for a prototype single-phase, high-speed flux-reversal generator. The performance analysis of the prototype based on the flux-MMF diagram technique is included, and this validates its capability in analysing new and non-conventional machines, which cannot be analysed using the classical means.

For biosensing applications it is often desirable to immobilise biomolecules securely on the electrode surface. The research described here was performed to develop and characterise modified conducting polymers suitable for use in the development of biosensor arrays. The research pursued centred around a post polymer-deposition modification strategy based on nucleophilic substitution of the pentafluorophenol group of the polymerised pyrrole derivative, pentafluorophenyl 3-(pyrrol-1-yl) propanoate (PFP). The activated ester present within this derivative is as an ideal reaction site for amine terminated species. Initially, electrochemical polymerisation growth conditions were determined and controlled to produce homopolymer and copolymer films with different structural and electrochemical characteristics. These polymer films were subsequently modified through various chemical reactions (e.g. with biotinylated species) to produce templates that could be used to biosensor developments. Furthermore, an important aspect in the development of a biosensing interface is the minimisation of non-specific adsorption and to that end a strategy was developed that involved modifying poly(PFP) films with poly(propyleneglycol) motifs. Usefully, an XPS based technique was developed to determine the extent of adsorption of labelled biological macromolecules on the modified poly(PFP) surfaces. Significantly, towards the development of a multianalyte biosensing substrate, a method was developed to control the reaction of solution based amine terminated species with the homopolymer poly(PFP). This involved electrochemically doping the polymer film to inhibit/promote nucleophilic reaction with amine containing species. Preliminary examples are given of the application of this technique was to micropattern species on multi-digitated electrodes.

This research project addresses the mitigation of voltage fluctuations using a series-connected power electronics-based controller, which belongs to the family of Flexible AC Transmission Systems (FACTS) controllers. These are emerging technologies which have been under continuous development for over a decade, and are now available to the electricity supply industry world-wide, helping to ameliorate a wide range of power system phenomena, to increase power transfers and stability margins. Voltage fluctuation is a complex phenomenon affecting adversely transmission and distribution networks. Bulky fluctuating load, wind farms and large induction motor are the major sources of voltage fluctuations. As the phenomenon propagates, it interacts with other voltage fluctuations contributed by different sources, and affecting neighbouring lighting circuits, giving raise to a phenomenon termed light flicker. To ameliorate such a problem, a well-coordinated operation of advanced voltage mitigation equipment, control strategy and specialised measurements instruments are required. Considerable progress has been made in voltage fluctuations mitigation using shunt FACTS controllers. However, very little work has been reported in tackling the very complex issue of mitigation of voltage fluctuation propagating in the network using series FACTS controllers. To advance this area of research, this project addresses the design and construction of a three-phase scaled-down TCSC prototype and a voltage fluctuations experimental environment, suitable for real-time hardware-in-the-loop testing. The research work carries out a fundamental study of TCSC resonances, which are termed resonance modes. It is found that a non-explicit resonance mode at a=90° exists, and it is termed intrinsic resonance mode. For a well-designed TCSC, only the fundamental and the intrinsic resonance mode should be active. To facilitate the design, a procedure has been identified, based in the synchronisation of resonance modes. To achieve mitigation successfully, a new tailor-made TCSC control strategy, named RT-DIMR, and a flexible virtual flickermeter based on the IEC-61000-4-15 standard are thoroughly developed and integrated under the same real-time computing platform. The RT-DIMR demonstrates its capability for controlling the TCSC under different voltage fluctuation conditions. The lEC-Flickermeter provides online flicker severity indices, information which may be used to asses whether or not the electrical network has been effectively improved. The aim of this research work is to experimentally evaluate the TCSC capabilities to mitigate travelling voltage fluctuations. A scaled-down network and voltage fluctuation sources are constructed to mimic a voltage fluctuations propagation environment. A comprehensive number of experiments are carried out to test the mitigation scheme under a wide range of conditions. The robustness and effectiveness of the mitigation schemes have been thoroughly demonstrated. The newly developed TCSC prototype, scaled-down testing environment and RT-DIMR control strategy recommend themselves not only as an imaginative voltage fluctuations mitigation research tool, but also as a general advanced FACTS research tool.

Wireless multi-user communication systems that operate in a low signal to interference noise ratio (SINR) region are studied in this thesis. This thesis examines a class of wireless communication systems that employs an adaptive receiver for multi-user symbol detection that operates in a low SINR (< 5 dB) region. Since the knowledge of channel-parameter estimates is unavailable at the receiver, a pilot (training) sequence is applied in the communication system, to learn the channel state information (CSI) at the receiver. In studying the classical view of a DFE, the mean square error (MSE) behaviour follows the bit error rate (BER) performance. Certain original results are obtained using the classical adaptive DFE to achieve minimum MSE, employing the least mean square (LMS) algorithm. The results thus obtained for an uncoded adaptive receiver system are applied to a coded system, transmitting either recursive systematic code (RSC) or turbo-code through a spread-spectrum multiuser multiple-path channel, which are referred to as two-stage and three-stage systems respectively in this thesis. The following claims are made based on the findings of this thesis: 1. It is known that a receiver implementing DFE can mitigate symbol-interference completely at high SINR. An adaptive LMS DFE realizes this by adapting the forward and backward filter coefficients with respective step-size constants. The classical approach to realizing interference mitigation was to set the forward and backward adaptation constants as the same. While this approach has provided interference mitigation at high SINR, it has been shown in this thesis that such an approach does not yield complete interference mitigation, even at high SINR. Instead, using different step-size constants at the backward and forward step-size constants provides the required optimality. 2. A decision feedback detector (DFD) mitigates the effects of interference on the information symbols that are transmitted through this communication channel. This thesis shows that an adaptive (LMS) DFD, using unequal compared to equal step-size constants to update the forward and backward filter coefficients, has a steady-state MSE improvement for an uncoded frequency selective communication channel. This thesis shows that, when the knowledge of CSI is not assumed to be known at a wireless receiver, a three-stage receiver has a BER performance improvement and operates at a lower SINR, without any additional computational complexity compared to a two-stage receiver.