Two types of solar cell AlGaAs-GaAs structures which are heteroface and triple heterojunction are investigated in this study. A complete theoretical study including optimisation for the optical properties ( transmission and reflection) of the heteroface Alo.sGao.2As- GaAs space solar cell is presented. The grid shadow and window layer effects, angle of incidence and the effects of the layer design parameters for AR-coating and window layer on the optical properties are considered in the calculations. A new structure for space solar cell which consists of double heterojunction AlGaAs­GaAs structure with GaAs/AlGaAs heterojunction back surface field (triple heterojunction(TIIJ))-to enhance the performance of the existed double heterojunction solar cell- is proposed. The analytical model for this TIU cell is presented as a function of all the cell's design parameters ( such as _layers doping, thicknesses, etc). The calculated results for this structure is compared with the experimental results for the previous double heterojunction structure. The effects of the design parameters of all layers including the AR-coating on the cell's output performance and the optimisation conditions are studied as well. The techniques of the light trapping and the photon recycling( which are gocxl for space solar cells) are applied for the THJ thin film AlGaAs-GaAs structure to improve further the efficiency . The change of the optimisation conditions due to the usage of these two techniques is also discussed.

The research described in this thesis has been carried out in three specific areas, namely the implementation and modification of pitch determination algorithms for speech signals, an investigation of the performance of the algorithms under different conditions of acoustic noise, and the real-time implementation of one of the algorithms using a high speed single-chip digital signal processor. The thesis presents a discussion on the applications of pitch determination algorithms for speech, followed by a description of the mechanism for human production and perception of speech signals. A modelling technique for the speech production mechanism is also introduced. Pitch determination algorithms for speech signals are discussed in detail, with particular reference to the two algorithms implemented during this research. Aspects of their implementation on a digital signal processing system based on an IBM PC-XT and commercially available signal processing software are described. Several important modifications to enhance the algorithms' performance have been carried out, and these are discussed in the thesis. Extensive tests under varying conditions of acoustic noise have been performed, and these are presented in the thesis. Results are presented and discussed, giving an indication of the effect of the noise on the performance of the algorithms. Finally, an implementation of a time domain pitch determination algorithm using a DSP device is presented, with detailed notes on the various aspects of the implementation. Results indicate that using appropriate AID hardware, the algorithm can achieve realtime pitch determination of speech.

The research described in this thesis was carried out in four specific areas, namely, Satellite-Switched Time-Division Multiple-Access (SSTDMA) network synchronisation, frame synchronisers, remote sensing satellite data decommutating systems, and prototype frame synchroniser implementation. In the area of SSTDMA network synchronisation, this thesis reports several new synchronisation methods based on an original on-board synchronisation concept. These new methods are shown to have some significant advantages over existing methods. Also reported is a new algorithm to determine the exact satellite position for the open-loop three ranging stations method. In the area of frame synchronisers, adaptive control strategies and post-detection processing techniques are proposed for a new form of frame synchroniser. This new frame synchroniser is shown to provide reliable and optimum frame synchronisation operation in an unpredictable noisy environment. A high-speed version of the new frame synchroniser is also proposed, and it is shown that the adaptive control strategies may be implemented using a microprocessor-based system. In the area of remote sensing satellite data decommutating systems, this thesis reports a new system. Compared with existing systems, the proposed new system offers greater flexibility and expandability, with data decommutation and distribution carried out in real-time. A prototype adaptive frame synchroniser with post-detection processing was constructed, and tested under various simulated environmental conditions. The design and hardware implementation of the prototype frame synchroniser are described. The abilities of the prototype frame synchroniser, such as various mode transition strategies, automatic polarity correction, bit slippage tolerance up to ±2 bits and a bit error rate (BER) tolerance up to 0.208, were demonstrated via a range of tests, which are described in this thesis.

Thin films of SnS have been deposited onto heated glass substrates using the thermal evaporation method and the chemical and physical properties of the layers determined and correlated to the deposition conditions and to post-deposition heat treatments. In particular scanning electron microscopy, energy dispersive X-ray analysis, X-ray di.ractrometry and Raman studies were used to determine the material properties, transmittance and reflectance spectroscopy to determine the optical constants and 4-probe and van der Pauw measurements to determine the electrical properties. The results indicate that for a wide range of deposition conditions it is possible to produce high quality layers of SnS that are free from pin-holes and cracks, that are made of densely packed grains, and that adhere strongly to the substrate. For substrate temperatures between 280°C to 360°C it is possible to produce single phase SnS layers. The energy bandgap of these layers was in the range 1.3eV to 1.35eV, was direct, and had an optical absorption coefficient α > 105 cm-1 for photons with energies greater than the energy bandgap. The electrical properties indicate that all the layers are p-conductivity type with resistivities in the range 40Ωcm to 100Ωcm. Solar cell devices were fabricated in the superstrate and substrate configurations using n-type cadmium sulphide (CdS) and zinc indium diselenide (ZIS) buffer layers to partner the p-type SnS. The devices were investigated by measuring the I-V characteristics in the dark, to determine the predominant conduction mechanisms, the I-V characteristics under illumination to determine the open-circuit voltage V, the short circuit current density Jsc, the fill factor FF and solar conversion efficiency of the devices, C-V studies to determine the doping profile in the SnS and the built-in voltage at the junction and spectral response measurements to determine the minority carrier diffusion length in the p-SnS. Devices made with CdS as the n-type partner had a high density of interface states (1.36 x 1011 F C-1cm-2) with low photovoltaic parameters and a negative band offset of -0.36 eV obtained (as measured using x-ray photoelectron spectroscopy). The best devices made were substrate configuration solar cells in which the back contact on glass was molybdenum and the bu.er layer was ZIS. These devices have Voc = 472 mV, Jsc = 16.1 mA/cm2 , FF = 0.38 and a solar conversion efficiency of 2.9%. This is a world record efficiency for SnS-based solar cells at the time of submission of this PhD thesis.

In this thesis a number of open problems in the theory of ordinary differential equations (ODEs) and dynamical systems are considered. The intention being to address current problems in the theory of systems control and synchronisation as well as enhance the understanding of the dynamics of those systems treated herein. More specifically, we address three central problems; the determination of exact analytical solutions of (non)linear (in)homogeneous ODEs of order 1 and 2, the determination of upper/lower bounds on solutions of nonlinear ODEs and finally, the synchronisation of dynamical systems for the purposes of secure communication. With regard to the first of these problems we identify a new solvable class of Riccati equations and show that the solution may be written in closed-form. Following this we show how the Riccati equation solution leads us quite naturally to the identification of a new solvable class of 2nd order linear ODEs, as well as a yet more general class of Riccati equations. In addition, we demonstrate a new alternative method to Lagrange's variation of parameters for the solution of 2nd order linear inhomogeneous ODEs. The advantage of our approach being that a choice of solution methods is offered thereby allowing the solver to pick the simplest option. Furthermore, we solve, by means of variable transforms and identification of the first integral, an example of the Duffing-van der Pol oscillator and an associated ODE that connects the equations of Lienard and Riccati. These fundamental results are subsequently applied to the problem of solving the ODE describing a lengthening pendulum and the matter of bounded controller design for linear time-varying systems. In addressing the second of the above problems we generalise an existing GrOnwall-like integral inequality to yield several new such inequalities. Using one of the new inequalities we show that a certain class of nonlinear ODEs will always have bounded solutions and subsequently demonstrate how one can numerically evaluate the upper limits on the square of the solution of any given ODE in this class. Finally, we apply our results to an academic example and verify our conclusions with numerical simulation. The third and final open problem we consider herein is concerned with the synchronisation of chaotic dynamical systems with the express intention of exploiting that synchronisation for the purposes of secure transmission of information. The particular issue that we concern ourselves with is the matter of limiting the amount of distortion present in the message arriving at the receiver. Since the distortion encountered is primarily a due to the presence of noise and the message itself we meet our ends by employing an observer-based synchronisation technique incorporating a proportional-integral observer. We show how the PI observer used gives us the freedom to reduce message distortion without compromising on synchronisation quality and rate. We verify our results by applying the method to synchronise two parameter-matched Duffing oscillators operating in a chaotic regime. Simulations clearly show the enhanced performance of the proposed method over the more traditional proportional observer-based approach under the same conditions. The structure of thesis is as follows: first of all we describe the motivation behind object of study before going on to give a general introduction to the theory of ODEs and dynamical systems. This lead-in also includes a brief history of the theory of ODEs and dynamical systems, a general overview of the subject (as wholly as is possible without getting into the mathematical detail that is left to the appendices) and concludes with a statement of the scope of the thesis as well as the contributions to knowledge contained herein. We then go on to state and prove our main results and contributions to the solution of those problems detailed above starting with the solution of ODEs.

Research into the modelling and analysis of microstrip patch antenna have been reported in many studies. These include Transmission Line Modelling, Cavity Modelling, Coplanar Multiport Modelling and Full wave Modelling. Since the electromagnetic field elements are time harmonic, the phasor-form of the Maxwell field equations is used. In this thesis results are presented of the research that has been carried out into the segmental approach for the analysis of the microwave patch antennas. The segmental approach includes the "Segmentation" and the "Desegmentation" methods. In the segmentation method two distinct structural forms have been identified, cascade and shunt types. In the cascade type all consecutive segment elements share a common boundary, while for the shunt type, all appended segment elements have no common boundary. In the case of the shunt type structure a generalised input impedance matrix formula, for any number of appended segment elements, has been obtained. For the desegmentation method a generalised input impedance for any number of deleted segment elements, has been obtained. The above research studies have been applied in the design of a circular polarised two corner deleted square patch microstrip antenna with a single feed. For this structure the design involves both square and triangular patch geometries. The overall patch geometry for circular polarised is determined using perturbation analysis to determine the size of the deleted triangular segment elements. New computationally efficient impedance coupling expressions for the interconnecting port impedances on a rectangle, and, on a right angled isosceles triangle shaped antenna patch have been derived. In the determination of the input impedance of the overall antenna structure the coupling impedances constitute the elements of the individual segment coupling matrices. The matrices are used in a general multiport matrix circuit analysis to obtain the input impedance formula. It is established that, where applicable, the desegmentation method is computationally more efficient than the segmentation method. The new results obtained have been applied to the design of a corner deleted square patch antenna, and, the design procedure is fully described. The computer program implementation evaluates the perturbation quantity, and, the antenna input impedance. The structural properties of the coupling matrices, which are used for efficient computation, are described in detail. All the results from the above work show close agreement with full-wave software simulation and practical results. Significant research achievements: Both segmentation and desegmentation methods have been studied and it has been shown that the desegmentation approach, when applicable, is in general significantly more computationally efficient. In the segmentation method two structural forms, cascade and shunt have been identified. In the latter case a new generalised input impedance matrix formula has been obtained for any number of appended segment elements. A new generalised input impedance matrix formula has been obtained for any number of deleted segment elements in the desegmentation method. New computationally efficient expressions for the coupling impedances have been derived and used in test applications. New computationally efficient expressions for the offset input impedance of a linear polarised rectangular patch, and, an isosceles right-angled triangular patch have been derived and experimentally verified. A program implementing the design procedure for the corner-deleted truncated square patch circular polarised microstrip antenna has been constructed using MATHCAD programming.

The aim of the work presented in this thesis was to develop CuInSe2 (CIS) and CuIni_„Al„Se2 (CIAS) thin films for application in photovoltaic (PV) solar cells. The purpose of the addition of aluminium (Al) in CIS thin films was to modify the energy band gap of the thin films to be nearer to the optimum for PV energy conversion and to replace the less abundant element, gallium (Ga) in CuIni_,,Ga,Se2 (CIGS) solar cells. This also makes possible the production of tandem solar cells using CIAS to make the wide energy band gap top cell and the CIS to make the narrow energy band gap lower cell. The use of very thin CIS and CIAS absorber layers in solar cell structures was also investigated; the aim was to reduce the amount of indium (In) in cell production. The CIS and CIAS absorber films were prepared by a sequential two step method in which Cu-In and Cu-In-Al precursor layers were magnetron sputter deposited onto Mo-coated soda lime glass (SLG) substrates; the CIS or CIAS was then formed by heating in a selenium (Se) containing environment. Thin film solar cells were developed in the substrate configuration and had the structure Ni-Al/Indium tin oxide (ITO)/i-ZnO/CdS/CIAS/Mo/SLG. In order to achieve high efficiency solar cells it is an important to optimse the back contact molybdenum (Mo) layer, the absorber layer, the CdS buffer layer, the window layer and top contact layers. The work described in this thesis focused on the optimisation of the back contact and absorber layers. The thin films were characterised mainly using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), secondary ion mass spectroscopy (MiniSIMS), atomic force microscopy (AFM) and using spectroscopy measurements to investigate the effect of processing conditions on the composition, crystal structure, surface morphology and the optical properties of the films. The solar cells were characterised by current-voltage (/- V) and incident photon-to-photocurrent conversion efficiency (IPCE) measurements. Both Mo single and bilayer structures were investigated. It was found that single layers had better properties than Mo bilayers. The optimisation of the Mo deposition sputtering process yielded Mo layers which had good adherence and were conformal to the glass substrates, had low resistivity (29 if .cm), were pin hole free and had good crystallinity. The influence of Cu-In precursor layers with thicknesses in the range 90-400 nm on the microstructure of the CIS thin films (thicknesses in the range 400-1600 nm) was investigated. Solar cells fabricated from the CIS films of thicknesses 500 nm and 900 nm yielded highest cell conversion efficiencies of 4.3% and 8.2%, respectively. The selenisation of the magnetron sputter deposited Cu-In-Al precursor layers was carried out at a temperature of 550°C. Films were poor in surface quality and adhesion. Films prepared from the precursor layer with n [(Al/(Al+In))] = 0.21 had a non-uniform Al depth profile towards the bottom of the film. Although the film was found to be photoactive its effective energy band gap was 0.98 eV suggesting the properties of CIS. This confirmed incomplete mixing of Al in the thin films which was considered to be segregated at the bottom of the film. The thinner layers of Cu-In-Al precursors with thicknesses in the range 0.55¬1.00 gm and n [(Al/Al+In)] in the range 0.28-0.54 were magnetron sputter deposited. The precursor layers showed the prominent binary A1Cu4 compound with a uniform distribution of Al in the layer. Thin films converted from these precursor layers of thicknesses in the range 1.3-2.0 pm were fairly uniform in surface structure. Films with x 0.2 were found to have an energy bandgap of 1.10 eV and were also photoactive. Solar cells fabricated from this absorber film yielded a highest cell efficiency of 4.9%. Environmental impact assessments have been made on materials and the processes used in the fabrication of CIS and CIAS.

In this thesis Genetic Algorithm Optimisation Methods (GA) is studied and for the first time used to design high efficiency microwave class E power amplifiers (PAs) and associated load patch antennas. The difficulties of designing high efficiency PAs is that power transistors are highly non linear and classical design techniques only work for resistive loads. There are currently no high efficient and accurate procedures for design high efficiency PAs. To achieve simplified and accurate design procedure, GA and new design quadratic equations are introduced and applied. The performance analysis is based on linear switch models and non linear circuitry push-pull methods. The results of the analytical calculations and experimental verification showed that the power added efficiency (PAE) of the PAs mainly depend on the losses of the active device itself and are nearly independent on the losses of its harmonic networks. Hence, it has been proven that the cheap material PCB FR4 can be used to design high efficiency class E PAs and it also shown that low Q factor networks have only a minor effect on efficiency, allowing a wide bandwidth to be obtained. In additional, a new procedure for designing class E PAs is introduced and applied. The active device (ATF 34143) is used. Good agreement was obtained between predicted analyses and the simulation results (from Microwave Office (AWR) and Agilent ADS software). For the practical realization, class E PAs were fabricated and tested using PCB FR4. The practical results validate computer simulations and the PAE of the class E PAs are more than 71% and Gain is over 3.8 dB when input power (Pin) is equal to 14 dBm at 2 GHz.

No description available.

This thesis describes a detailed study of advanced optical fibre sensors based on fibre Bragg grating (FBG), tilted fibre Bragg grating (TFBG) and long-period grating (LPG) and their applications in optical communications and sensing. The major contributions presented in this thesis are summarised below. The most important contribution from the research work presented in this thesis is the implementation of in-fibre grating based refractive index (RI) sensors, which could be the good candidates for optical biochemical sensing. Several fibre grating based RI sensors have been proposed and demonstrated by exploring novel grating structures and different fibre types, and employing efficient hydrofluoric acid etching technique to enhance the RI sensitivity. All the RI devices discussed in this thesis have been used to measure the concentration of sugar solution to simulate the chemical sensing. Efforts have also been made to overcome the RI-temperature cross-sensitivity for practical application. The demonstrated in-fibre grating based RI sensors could be further implemented as potential optical biosensors by applying bioactive coatings to realise high bio-sensitivity and bio-selectivity. Another major contribution of this thesis is the application of TFBGs. A prototype interrogation system by the use of TFBG with CCD-array was implemented to perform wavelength division multiplexing (WDM) interrogation around 800nm wavelength region with the advantages of compact size, fast detection speed and low-cost. As a high light, a novel in-fibre twist sensors utilising strong polarisation dependant coupling behaviour of an 81°-TFBG was presented to demonstrate the high torsion sensitivity and capability of direction recognition.