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.

Most of the analysis techniques available for planning and operation of multiphase power systems are based upon the assumption that the network operates under perfectly balanced conditions. The advantage of this assumption from the modelling view point is that only one phase of the three phase system needs to be considered for analysis, resulting in a reduced size of the problem at hand. However, the phase frame of reference offers a more general representation for the solution of power system problems than the frame of reference provided by the sequences. The former can accommodate networks containing any degree of unbalance whilst the latter is only applicable to power networks exhibiting perfect or near-perfect impedance balance between phases. The thesis reports on the development of steady state and time domain models of Flexible AC Transmission System (FACTS) controllers in the natural framework of electric systems, i.e. namely the phase co-ordinates domain. The FACTS equipment selected for analytical development in this research are: the static synchronous compensator (STATCOM), the static synchronous series compensator (SSSC), the unified power flow controller (UPFC) and the high-voltage direct current (HVDC). These power electronics-based controllers have the voltage source converter as their main constituent. The combined solution of both steady state and dynamic power flow equations pertaining to the VSC-based FACTS controllers and the power network are fully described in the thesis. The steady-state mathematical models of VSC-based FACTS controllers are formulated in nodal form using the frame of reference of the phases. Guidelines for their implementation into two distinct power flows algorithm namely, the Newton-Raphson in polar co-ordinates and the Newton-Raphson in rectangular coordinates are given. For the purpose of long-term dynamic assessment, a simultaneous solution using implicit trapezoidal integration method with Newton iteration is used to solve the set of differential-algebraic equations of generating plants and network components. In order to assess both the steady state and the dynamic behaviour of the models developed, a comprehensive, newly developed integrated software environment is used.

Electron beam lithography is capable of defining structures with sub-10 nm linewidths. To exploit this capability to produce working devices with structures defined in multiple 'lithographic steps' a process of alignment must be used. The conventional method of scanning the electron beam across simple geometrically shaped markers will be shown inherently to limit the alignment accuracy attainable. Improvements to alignment allow precise placement of elements in complex multi-level devices and may be used to realise structures which are significantly smaller than the single exposure resist limit. Correlation based alignment has been used previously as an alignment technique, providing improvements to the attainable accuracy and noise immunity of alignment. It is well known that the marker pattern used in correlation based alignment has a strong influence on the magnitude of the improvements that can be realised. There has, to date, however, been no analytical study of how the design of marker pattern affects the correlation process and hence the alignment accuracy possible. This thesis analyses the correlation process to identify the features of marker patterns that are advantageous for correlation based alignment. Several classes of patterns have been investigated, with a range of metrics used to determine the suitability and performance of each type of pattern. Penrose tilings were selected on this basis as the most appropriate pattern type for use as markers in correlation based alignment. A process for performing correlation based alignment has been implemented on a commercial electron beam lithography tool and the improvements to the alignment accuracy have been demonstrated. A method of measuring alignment accuracy at the nanometer scale, based on the Fourier analysis of inter-digitated grating has been introduced. The improvements in alignment accuracy realised have been used to facilitate the fabrication of 'nanogap' and 'nanowire' devices - structures which have application in the fields of molecular electronics and quantum conduction. Fabrication procedures for such devices are demonstrated and electrical measurements of such structures presented to show that it is a feasible method of fabrication which offers much greater flexibility than the existing methods for creating these devices.

In this work, the need for an integrated optical dispersive device is discussed, with particular reference to pulse compression of semiconductor mode-locked laser (MLL) pulses that exhibit temporal chirp and therefore, worse than transform limited behaviour. It is shown that current techniques in fibre and integrated dispersion control do not overlap the dispersion regime presented, making it necessary to design a new integrated device for this purpose. A monolithic chirped Bragg grating is presented with dispersion and bandwidth characteristics coinciding with the previously mentioned regimes. The device, based on a deeply etched tapered waveguide design, may be fabricated fully post-growth, lending it a significant advantage over current grating designs that require the pattern to be written into the core material and the upper cladding layers subsequently overgrown. The deeply etched sidewall grating structures provide the requisite high coupling coefficients, and the ability to induce arbitrary apodisation profiles, while the tapered waveguide design allows the same freedom the grating Bragg condition profile. The coupled-mode analysis for a chirped grating structure is presented and used as a basis for a Transfer Matrix Method (TMM) representation of the device. This simulation tool allows modelling of the arbitrary Bragg condition and apodisation profiles for steady state analysis of passive grating devices, Distributed Feedback (DFB) and Distributed Bragg Reflector (DBR) lasers. The fabrication of low loss passive grating devices and DFB lasers is described with particular attention paid to lithography and reactive ion etching methods. In addition, work is presented on a wet chemical oxidation technique for reduction of sidewall roughness in A1GaAs based waveguides. Deeply etched waveguides were shown to exhibit losses reduced by up to 4dBcm[superscript-1] after application of this procedure. The fabricated passive grating devices exhibit transmission and grating phase profiles closely matching those predicted by the simulations, with control shown over both Bragg condition and coupling coefficient. The DFB lasers, again in agreement with simulation, show unique multi-mode behaviour, closely related to the chirped grating modulation profile. Also presented is a method by which sub-100 [m] tapers for transitions between shallow etched and deep etched waveguides may be fabricated for quasi-adiabatic propagation. These tapers provide a means by which integration may be achieved between optical systems with different mode profiles, these being defined by device properties, for example integration of small radius bends and waveguide gain structures. A simulation tool based on teh TMM is derived and a set of optimised tapers are fabricated, their results matched to the simulations. Low loss, low reflectivity tapers are exhibited with properties in close agreement with teh TMM and Finite Difference Time Doain (FDTD) simulations.

The research described work in this thesis is concerned with the development and realisation of high brightness array laser diodes operating in single spatial mode. The fabrication of the high brightness laser devices was carried out on 830 nm GaAs/AlGaAs material system. Broad area lasers were fabricated to evaluate the material quality. The material design was based on the high d/Г concept, by which the optical power is maximised prior to thermal roll-over or the catastrophic optical mirror damage (COMD). A quantum well intermixing (QWI) process was developed for integrating the non absorbing mirrors (NAMs), the gain section, the MMI coupler and the single spatial mode output waveguide. The quantum well intermixing (QWI) was used to fabricate nonabsorbing mirrors (NAMs) with a blue shift of 58 nm. The annealing for the optimum process was 810º C for 90 seconds. The QWI was evaluated using the photoluminescence method, band gap shift of 58 nm was realised. The fabricated NAMs ranged from 30 to 100 μm in length. The gain section length was set at 975 μm. In the passive sections, the MMI and output waveguide are 1 mm long. The total device length was around 2 mm. No COMD was observed in the fabricated devices meaning that the quantum well intermixing has worked well. The propagation loss measurement for 830 nm passive waveguide, intermixed with a QWI blue shifted 58 nm and 9.8 mm long was 4.48 dB/cm. This is comparable to the loss that was measured from broad area laser material, which had a loss of 6.9 dB/cm. Fimmwave and beam propagation method (BPM) were used for the modelling. The results of the modelling for the single mode ridge waveguide were that, a ridge depth of 1.84 μm supported a single mode. The selected ridge width was 2.5 μm. Modelling of a 1x4 MMI array laser and a 1x2 MMI array was undertaken using the beam propagation method (BPM). The optimum lateral spacing of the gain waveguides was found to be in a range of 2.5-3.5 μm for high power operation. In the 1x4 MMI array laser, the phase was modelled. The inner gain sections have a phase difference of π/2 with respect to the outer gain sections, while the 1x2 MMI array laser has zero phase shift between the two gain sections. 1x4 and 1x2 MMI array lasers were fabricated. In the case of 1x4 MMI array laser, different MMI coupler lengths were fabricated. The MMI lengths were between 617 μm and 709 μm. The devices were tested electrically using 10 μs pulses and a 1 KHz repetition rate. They were tested to a Abstract iii current level of 22xIth. The power achieved was > 440 mW in pulsed mode from the single output facet. This power was equivalent to an optical intensity of 17.6 MW/cm2. The threshold current measured for the device was 145 mA. The external quantum efficiency (ηext) was 32.1 %. The MMI array laser device design with an MMI width of 24 μm, length of 617 μm and gain section spacing of 3.5 μm had a strong phase locking up to an applied current of 5.2xIth. The far-field pattern width of the central lobe of the phase locked 1x4 MMI array laser was 2.1 º measured from the array facets side. This value is comparable to the diffraction limited value of 1.96 º calculated simply from (λ/N.p). The quality factor (M2 emitter) for the 2.5 μm wide single ridge emitter was estimated to be close to 1. The beam quality factor of the 1x4 MMI array bar (M2 bar) was estimated to be 1.07. The visibility (V) of the pattern was very close to 1. The phase locked power (P) was 152.0 mW per facet for an operating current of 5.2xIth (Ith=145 mA). The corresponding brightness was 19.6 MW/cm2.sr. The operating wavelength for a 1x4 MMI laser diode array was a 0.822 μm. The single emission wavelength was measured from the four array side with a narrow spectral width (Δλ) of 0.22 nm at the FWHM for an operating current of 5.2xIth. The narrow spectral width of 0.22 nm for the array was a much smaller than that for a ridge waveguide laser. The ridge waveguide laser had a spectral width of a 0.65 nm at FWHM. This spectral width was measured for a current of 200 mA in pulsed mode with a 5 μs pulse width. The lasing spectra of the array showed four individual peaks, when the current was increased to 6.2xIth. At this point, the array is no longer phase locked. The wavelength peaks were as follows: λ1=821.35 nm, λ2=821.59 nm, λ3=821.83 nm and λ4=822.08 nm, respectively. The spectral width (Δλ) was around 0.22 nm at FWHM for the each of the individual peaks. The 1x2 MMI array devices were pulsed to a current level of 30xIth. The output power was around 332 mW from the single output facet. The threshold current was 85 mA. The largest optical output power was realised for the device with an MMI length of 480 μm. The external quantum efficiency was around 33%. The phase relationship between the gain sections for the 1x2 MMI array laser is an identical one (i.e.Ф1=Ф2). The phase locking was achieved in the 1x2 MMI array laser. However, the phase locking was only evident up to 3xIth (Ith=85 mA) CW. The width of the central lobe of the far-field pattern was 4.49 º (equivalent to 1.33x the diffraction limit). There was also a reasonable correlation between the far-field pattern from the measurement and the far-field pattern from the simulation. The quality Abstract iv factor for the emitter (M2 emitter) was 1, while the beam quality factor (M2 bar) of the 1x2 MMI array (bar) was estimated to be 1.33. The visibility (V) of the pattern was estimated to be around 0.5. The lasing spectra showed a single wavelength emission with a peak of 823.55 nm and a very narrow spectral width of 0.3 nm at the FWHM. The optical power at an injection current of 3.2xIth was a mere 60mW CW per facet, which corresponded to a brightness of 5.02 (MW/cm2. sr). The results for a 1x2 MMI laser array indicated that the length of the MMI section promoted the phase locking. An accurately designed MMI length resulted in a narrow spectral width of 0.3 nm at FWHM for an MMI length of 480 μm. The spectral width increased with a reduction of the MMI length. The spectral width was 0.86 nm at FWHM for an MMI length of 465 μm, whereas it increased to 3.1 nm at the FWHM for an MMI length of 444 μm. Therefore, the phase locking and the bandwidth of the 1xN MMI array laser is a self imaging and MMI cavity length dependent.

Global demand for renewable energy is at an all-time high. Renewable energy can be extracted from naturally available resources such solar, wind, tides, geothermal heat, sea waves and the others. The percentage of renewable energy in the energy resources is increasing at an ever increasing rate. While much renewable energy is large scale, it is also suitable for rural and remote areas. The challenges facing today’s renewable energy supply industry are many, especially in the wave energy field which is still underdeveloped. The number of commercialised wave energy devices is very limited and the concepts implemented for harnessing wave energy are very different between the different devices and often struggle to be effective or survive ocean-going conditions. Thus, major research is required to find new and effective methods for harnessing wave energy which are able to supply power to the grid with high conversion rate and good reliability. The proposed Bristol cylinder device, in theory, should be able to harness sea wave energy and to convert it into useful electricity, and this device is studied in detail here. This device is still new in terms of practical application in ocean conditions. It needs power electronics and effective controllers for high-efficiency power extraction and to be successfully integrated into the power grid. When the device was first investigated in the 1970s, power electronics and variable-speed brushless permanent-magnet machinery was simply not developed to the level it is today, hence the revisiting of this device several decades later. A successful Bristol cylinder wave device which can extract renewable energy may well impact on the renewable energy sector. The wave characteristics were studied and simulated using Airy Linear Wave Theory and Stoke’s Second Order Theory. The dynamic characteristics of the Bristol cylinder are investigated when interacting with waves, together with the control necessary to make it a functioning device. A lab scale wave tank suitable to test the Bristol cylinder is designed. A surface magnet permanent magnet synchronous generator (PMSG) design is considered in this research project. This generator configuration shows its suitability in producing high conversion-rate power when working in a low speed environment. The sizing exercise is performed to determine the size of the lab scale PMSG. Analytical analysis and finite element analysis is performed to study the performance of the designed PMSG. A study of the effect of the armature length with the corresponding incident wave is done. Field oriented control (FOC) is applied to control the speed of the generator. FOC is shown to be suitable for stable control of the generator speed. Simulations using MATLAB are utilized and Simulink is used to construct the model and evaluate the potential performance of the control system design. In this thesis, theoretical analyses and simulations of the generator performances are carried out for several generator topologies and sizes. The grid side converter controller technique is also simulated in MATLAB/Simulink and the performance evaluated.

This thesis presents an investigation into the feasibility of tunable, monolithically integrated, nonlinear optical frequency conversion sources which work under the principles of an optical parametric oscillator (OPO). The room-temperature continuous wave (CW) operation of these devices produces narrow line-width, near- and mid-infrared wavelengths, primarily used in chemical sensing applications. The devices detailed here, based on the GaAs–AlGaAs superlattice material system, benefit from post growth, ion implantation induced, quantum well intermixing, to achieve 1st order phase matching. The experiments, which have been performed to optimize the second-order nonlinear processes in our GaAs–AlGaAs superlattice waveguides, have demonstrated improved conversion efficiencies when compared to the performance achieved previously in similar superlattice nonlinear waveguides. We have achieved pulsed type-I phase matched second harmonic generation (SHG) with powers up to 3.65 μW (average pulse power), CW type-I phase matched SHG up to 1.6 μW for the first time, and pulsed type-II phase matched SHG up to 2 μW (average pulse power), again for the first time. Moreover, we have been able to achieve both CW type-I and CW type-II phase matched difference frequency generation, which converts C-band wavelengths into L- and U-band wavelengths, over at least a 20 nm conversion bandwidth. These results have been made possible through the systematic optimization of processes developed to fabricate nonlinear optical waveguides. Fabrication processes have also been developed to facilitate the incorporation of on-chip lasers and optical routing components, required to achieve a fully integrated OPO and nonlinear optical frequency converter. The optical routing in these devices has been demonstrated using a frequency selective multi-mode interference (MMI) coupler. The superlattice laser material has been designed by optimizing the material structure and employing different growth technologies. Room-temperature CW laser action has been achieved in 100 nm thick, superlattice core, half-ring lasers. The laser excitation is measured at 801 nm, and the internal power of the on-chip pump is estimated to be in excess of 200 mW in a full-ring, after accounting for optical routing, linear, bending and nonlinear losses. We have been able to conclude that our designed OPO and frequency converter is just feasible with the performance achieved in different components.