This thesis describes an investigation of polarisation conversion effects in gallium arsenide optical waveguides. The research was carried out with the aims of predicting, preventing and harnessing such effects. Experimental results are presented to demonstrate changes in the polarisation state of light propagating in passive deep-etched waveguides. The results are described by established modelling techniques. The effect due to process-dependent features of waveguide cross-section geometry, in particular asymmetry resulting form non-vertical etching, is investigated. The polarisation angles of hybrid waveguide modes are measured, and a novel technique is presented for the measurement of the differences been the effective indices of orthogonally polarised modes. The measurements obtained are used to analyse the evolution of elliptical polarisation states during propagation, and to provide an account of the physical origin of the polarisation conversion. Details of the nature of the optical modes predicted by rigorous numerical method simulations are demonstrated by the experimental results, while quantitative agreement between the simulated and measured data is shown. A simplified account of the behaviour is provided using a coupled-mode formulation. The influence of the linear electrooptic effect in modifying the polarisation conversion behaviour is explored experimentally, and is described using established theory. Waveguide designs are obtained which prevent unintended polarisation conversion in the presence of identified causes, while maintaining the main waveguide parameters of material composition, optical mode size and shape, electrooptic performance, and fabrication process. The polarisation behaviour in waveguides fabricated to these designs is evaluated, and the expected performance benefits are confirmed. A novel waveguide device which provides electrooptic control and switching of the optical polarisation state is presented. The device is capable of converting any input polarisation state into an arbitrary output state using the linear electrooptic effect. A working design is obtained and the fabrication of devices is described. Experimental results are presented which demonstrate the concept. Further developments of the polarisation controller device are proposed, including the realisation of the potential for switching speeds at frequencies of tens of GHz.

Generating high-fidelity images in real-time at reasonable frame rates, still remains one of the main challenges in computer graphics. Furthermore, visuals remain only one of the multiple sensory cues that are required to be delivered simultaneously in a multi-sensory virtual environment. The most frequently used sense, besides vision, in virtual environments and entertainment, is audio. While the rendering community focuses on solving the rendering equation more quickly using various algorithmic and hardware improvements, the exploitation of human limitations to assist in this process remain largely unexplored. Many findings in the research literature prove the existence of physical and psychological limitations of humans, including attentional, perceptual and limitations of the Human Sensory System (HSS). Knowledge of the Human Visual System (HVS) may be exploited in computer graphics to significantly reduce rendering times without the viewer being aware of any resultant image quality difference. Furthermore, cross-modal effects, that is the influence of one sensory input on another, for example sound and visuals, have also recently been shown to have a substantial impact on viewer perception of virtual environment. In this thesis, auditory-visual cross-modal interaction research findings have been investigated and adapted to graphics rendering purposes. The results from five psychophysical experiments, involving 233 participants, showed that, even in the realm of computer graphics, there is a strong relationship between vision and audition in both spatial and temporal domains. The first experiment, investigating the auditory-visual cross-modal interaction within spatial domain, showed that unrelated sound effects reduce perceived rendering quality threshold. In the following experiments, the effect of audio on temporal visual perception was investigated. The results obtained indicate that audio with certain beat rates can be used in order to reduce the amount of rendering required to achieve a perceptual high quality. Furthermore, introducing the sound effect of footsteps to walking animations increased the visual smoothness perception. These results suggest that for certain conditions the number of frames that need to be rendered each second can be reduced, saving valuable computation time, without the viewer being aware of this reduction. This is another step towards a comprehensive understanding of auditory-visual cross-modal interaction and its use in high-fidelity interactive multi-sensory virtual environments.

The primary outcome of this research project is the development of a methodology enabling fast automated early-stage power and energy analysis of configurable processors for system-on-chip platforms. Such capability is essential to the process of selecting energy efficient processors during design-space exploration, when potential savings are highest. This has been achieved by developing dynamic and static energy consumption models for the constituent blocks within the processors. Several optimisations have been identified, specifically targeting the most significant blocks in terms of energy consumption. Instruction encoding mechanism reduces both the energy and area requirements of the instruction cache; modifications to the multiplier unit reduce energy consumption during inactive cycles. Both techniques are demonstrated to offer substantial energy savings. The aforementioned techniques have undergone detailed evaluation and, based on the positive outcomes obtained, have been incorporated into Cascade, a system-on-chip coprocessor synthesis tool developed by Critical Blue, to provide automated analysis and optimisation of processor energy requirements. This thesis details the process of identifying and examining each method, along with the results obtained. Finally, a case study demonstrates the benefits of the developed functionality, from the perspective of someone using Cascade to automate the creation of an energy-efficient configurable processor for system-on-chip platforms.

This thesis details the analysis and design of ultra-low power radio transceivers operating at microwave frequencies. Hybrid prototypes and Monolithic Microwave Integrated Circuits (MMICs) which achieve power consumptions of less than 1 mW and theoretical operating ranges of over 10 m are described. The motivation behind the design of circuits exhibiting ultra low power consumption and, in the case of the MMICs, small size is the emerging technology of Wireless Sensor Networks (WSN). WSNs consist of spatially distributed ‘nodes’ or ‘specks’ each with their own renewable energy source, one or more sensors, limited memory, processing capability and radio or optical link. The idea is that specks within a ‘speckzone’ cooperate and share computational resources to perform complex tasks such as monitoring fire hazards, radiation levels or for motion tracking. The radio section must be ultra low power e.g. sub 1 mW in order not to drain the limited battery capacity. The radio must also be small in size e.g. less than 5 x 5 mm so that the overall speck size is small. Also, the radio must still be able to operate over a range of at least a metre so as to allow radio contact between, for example, rooms or relatively distant specks. The unsuitability of conventional homodyne topologies to WSNs is discussed and more efficient methods of modulation (On-Off Keying) and demodulation (non-coherent) are presented. Furthermore, it is shown how Super-Regenerative Receivers (SRR) can be used to achieve relatively large output voltages for small input powers. This is important because baseband Op-Amps connected at the RF receiver output generally cannot amplify small signals at the input without the output being saturated in noise (10mV is the smallest measured input for 741 Op-Amp). Instrumentation amplifiers are used in this work as they can amplify signals below 1mV. The thesis details the analysis and design of basic RF building blocks: amplifiers, oscillators, switches and detectors. It also details how the circuits can be put together to make transceivers as well as describing various strategies to lower power consumption. In addition, novel techniques in both circuit and system design are presented which allow the power consumption of the radio to be reduced by as much as 97% whilst still retaining adequate performance. These techniques are based on duty cycling the transmitter and receiver and are possible because of the discontinuous nature of the On-Off Keying signal. In order to ease the sensitivity requirements of the baseband receive amplifier a design methodology for large output voltage receivers is presented. The designed receiver is measured to give a 5 mV output for an input power of -90 dBm and yet consumes less than 0.7 mW. There is also an appendix on the non linear modelling of the Glasgow University 50nm InP meta-morphic High Electron Mobility Transistor (50nm mHEMT) and one on the non linear modelling of a commercial Step Recovery diode (SRD). Models for the 50 nm mHEMT and the SRD are useful in the analysis, simulation and design of oscillators and pulse generators respectively.

This thesis proposes a new, highly generalised and fundamental, information-modelling framework called the TRM (Ternary Relations Model). The TRM was designed to be a model for converging a number of differing paradigms of information management, some of which are quite isolated. These include areas such as: hypertext navigation; relational databases; semi-structured databases; the Semantic Web; ZigZag and workflow modelling. While many related works model linking by the connection of two ends, the TRM adds a third element to this, thereby enriching the links with associative meanings. The TRM is a formal description of a technique that establishes bi-directional and dynamic node-link structures in which each link is an ordered triple of three other nodes. The key features that makes the TRM distinct from other triple-based models (such as RDF) is the integration of bi-directionality, functional links and simplicity in the definition and elements hierarchy. There are two useful applications of the TRM. Firstly it may be used as a tool for the analysis of information models, to elucidate connections and parallels. Secondly, it may be used as a “construction kit” to build new paradigms and/or applications in information management. The TRM may be used to provide a substrate for building diverse systems, such as adaptive hypertext, schemaless database, query languages, hyperlink models and workflow management systems. It is, however, highly generalised and is by no means limited to these purposes.

The ever increasing demand for higher power devices at higher frequencies has prompted much research recently into the aluminium nitride/gallium nitride high electron mobility transistors (AlN/GaN HEMTs) in response to theoretical predictions of higher performance devices. Despite having superior material properties such as higher two-dimensional electron gas (2DEG) densities and larger breakdown field as compared to the conventional aluminium gallium nitride (AlGaN)/GaN HEMTs, the AlN/GaN devices suffer from surface sensitivity, high leakage currents and high Ohmic contact resistances. Having very thin AlN barrier layer of ∼ 3 nm makes the epilayers very sensitive to liquids coming in contact with the surface. Exposure to any chemical solutions during device processing degrades the surface properties, resulting in poor device performance. To overcome the problems, a protective layer is employed during fabrication of AlN/GaN-based devices. However, in the presence of the protective/passivation layers, formation of low Ohmic resistance source and drain contact becomes even more difficult. In this work, thermally grown aluminium oxide (Al2O3) was used as a gate di- electric and surface passivation for AlN/GaN metal-oxide-semiconductor (MOS)-HEMTs. Most importantly, the Al2O3 acts as a protection layer during device processing. The developed technique allows for a simple and effective wet etching optimisation using 16H3PO4:HNO3:2H2O solution to remove Al from the Ohmic contact regions prior to the formation of Al2O3 and Ohmic metallisation. Low Ohmic contact resistance (0.76Ω.mm) as well as low sheet resistance (318Ω/square) were obtained after optimisation. Significant reduction in the gate leakage currents was observed when employing an additional layer of thermally grown Al2O3 on the mesa sidewalls, particularly in the region where the gate metallisation overlaps with the exposed channel edge. A high peak current ∼1.5 A/mm at VGS=+3 V and a current-gain cutoff frequency, fT , and maximum oscillation frequency, fMAX , of 50 GHz and 40 GHz, respectively, were obtained for a device with 0.2 μm gate length and 100 μm gate width. The measured breakdown voltage, VBR, of a two-finger MOS-HEMT with 0.5μm gate length and 100 μm gate width was 58 V. Additionally, an approach based on an accurate estimate of all the small-signal equivalent circuit elements followed by optimisation of these to get the actual element values was also developed for AlN/GaN MOS-HEMTs. The extracted element values provide feedback for further device process optimisation. The achieved results indicate the suitability of thermally grown Al2O3 for AlN/GaN-based MOS-HEMT technology for future high frequency power applications.

The work deals with the modelling and optimisation of reverse osmosis (RO) spiral wound elements. It is aimed at improving areas of uncertainty and possible limitations which remain with current published predictive schemes. These were compromised mainly by the lack of adequate experimental data representative of actual operating conditions. Two different mathematical models, termed the `Slit' and the `Spiral' model, were developed. These models differ on the geometrical idealisation of a spiral wound element as indicated by their names. The Solution Diffusion model is used to describe water and salt transport across the membrane. The differential equations governing the process were solved numerically using a finite difference method. The resulting computer programs enable concentrations, pressures and flow rates in the brine and permeate channels to be obtained at any point in the module. The investigation covered a wide range of feed conditions by using experimental data provided from two different types of commercial spiral wound modules. These were the ROGA-4160HR [29] and the Filmtec FT30SW2540 [28] modules. The former type dealt with data typical of brackish water desalination whereas the second type provided data typically encountered in sea-water desalination. The required intrinsic membrane characteristics were determined experimentally using small samples of membrane in a test cell in a closed loop system. For both models, the predictions agree very well with the experimental data over the entire range of operating conditions:- with the exception of some few cases, typical deviations were of the order of 6% for the module productivity and of about 10% for the permeate quality. In addition, parametric studies were performed to establish the programs consistency and the results were in accordance with the theory.

This thesis reports on Semiconductor Optical Amplifiers (SOAs) and their use in optical communication systems; in particular improving the reach of Passive Optical Networks (PON). Following a comprehensive overview of the components of optical communication systems a PON is introduced and the standard of Gigabit-PON (GPON) explained. The concept of extending the reach of GPON through the introduction of amplification is presented and the business drivers of the telecommunication operators detailed. The physics of SOAs are described followed by the parameters used to characterise them. Carrier dynamics of SOAs are explained and the methods of measurement of the carrier dynamics are detailed including the spectrogram technique. This method simultaneously measures the gain and phase recovery which is desirable for applications in long range telecommunications which require unchirped signals with a fast response for both gain and phase. Parameters of commercially available SOAs are compared with the requirements to extend the reach of PONs. Following this the fabrication tolerances for SOAs insensitive to polarisation dependent gain (PDG) are modelled. Results from SOA modelling showed that the greatest contributing factor to PDG variation was the active region thickness error. In the context of bulk production this requires a realistic tolerance of ~10nm to maintain PDG of ~1dB. A polarisation insensitive high gain SOA is designed and experimentally measured. This SOA is measured in the context of GPON and shown to extend the reach of the current standard by a record margin of 28dB. The limitation of the improvement is attributed to gain modulation sourced intersymbol interference (the patterning effect). The patterning effect has been reported in literature to be reduced through the introduction of SOAs with an active region made from quantum dot (Qdot) material. A comparative study of the gain and phase recovery time and alpha factor of various dimensional SOAs is presented. Using the spectrogram method it is shown that reducing the power and increasing the bias of the SOA can reduce the carrier recovery time. A Qdot active region SOAs is shown to considerably reduce the gain recovery time compared to a bulk SOA of similar length. The active region of the Qdot SOA alludes to a faster carrier recovery time which could be beneficial to extend the reach of PONs without patterning. However as these are more difficult to fabricate in mass production it is unknown if they are a viable solution on a commercial scale. In the context of GPON a low alpha factor is desired for minimizing chirp and phase nonlinearities during amplification of short pulses. An alpha factor study is presented and the Qdot SOA was measured to have the lowest alpha factor which could be beneficial for reducing chirp in 10G-PON.

Flexible rotor-bearing system stability is a very important subject impacting the design, control, maintenance and operating safety. As the rotor bearing-system dynamic nonlinearities are significantly more prominent at higher rotating speeds, the demand for better performance through higher speeds has rendered the use of linear approaches for analysis both inadequate and ineffective. To address this need, it becomes important that nonlinear rotor-dynamic responses indicative of the causes of nonlinearity, along with the bifurcated dynamic states of instabilities, be fully studied. The objectives of this research are to study rotor-dynamic instabilities induced by mass unbalance and to use smart materials to stabilise the performance of the flexible rotor-system. A comprehensive mathematical model incorporating translational and rotational inertia, bending stiffness and gyroscopic moment is developed. The dynamic end conditions of the rotor comprising of the active bearing-induced axial force is modelled, the equations of motion are derived using Lagrange equations and the Rayleigh-Ritz method is used to study the basic phenomena on simple systems. In this thesis the axial force terms included in the equations of motion provide a means for axially directed harmonic force to be introduced into the system. The Method of Multiple Scales is applied to study the nonlinear equations obtained and their stabilities. The Dynamics 2 software is used to numerically explore the inception and progression of bifurcations suggestive of the changing rotor-dynamic state and impending instability. In the context of active control of flexible rotors, smart materials particularly SMAs and piezoelectric stack actuators are introduced. The application of shape memory alloy (SMA) elements integrated within glass epoxy composite plates and shells has resulted in the design of a novel smart bearing based on the principle of antagonistic action in this thesis. Previous work has shown that a single SMA/composite active bearing can be very effective in both altering the natural frequency of the fundamental whirl mode as well as the modal amplitude. The drawback with that design has been the disparity in the time constant between the relatively fast heating phase and the much slower cooling phase which is reliant on forced air, or some other form of cooling. This thesis presents a modified design which removes the aforementioned existing shortcomings. This form of design means that the cooling phase of one half, still using forced air, is significantly assisted by switching the other half into its heating phase, and vice versa, thereby equalising the time constants, and giving a faster push-pull load on the centrally located bearing; a loading which is termed ‘antagonistic’ in this present dissertation. The piezoelectric stack actuator provides an account of an investigation into possible dynamic interactions between two nonlinear systems, each possessing nonlinear characteristics in the frequency domain. Parametric excitations are deliberately introduced into a second flexible rotor system by means of a piezoelectric exciter to moderate the response of the pre-existing mass-unbalance vibration inherent to the rotor. The intended application area for this SMA/composite and piezoelectric technologies are in industrial rotor systems, in particular very high-speed plant, such as small light pumps, motor generators, and engines for aerospace and automotive application.

The current generation of wind turbines that are being deployed around the world features, almost exclusively, a three-bladed rotor with a horizontal-axis configuration. In recent years, however, a resurgence of interest in the vertical-axis wind turbine configuration has been prompted by some of its inherent advantages over horizontal-axis rotors, particularly in flow conditions that are typical of the urban environment. The accurate modelling of the aerodynamics of vertical-axis wind turbines poses a significant challenge. The cyclic motion of the turbine induces large variations in the angle of attack on the blades during each rotor revolution that result in significant unsteadiness in their aerodynamic loading. In addition, aerodynamic interactions occur between the blades of the turbine and the wake that is generated by the rotor. Interactions between the blades of the turbine and, in particular, tip vortices that were trailed in previous revolutions produce impulsive variations in the blade aerodynamic loading, but these interactions are notoriously difficult to simulate accurately. This dissertation describes the application of a simulation tool, the Vorticity Transport Model (VTM), to the prediction of the aerodynamic performance of three different vertical-axis wind turbines - one with straight blades, another with curved blades and a third with a helically twisted blade configuration - when their rotors are operated in three different conditions. These operating conditions were chosen to be representative of the flow conditions that a vertical-axis wind turbine is likely to encounter in the urban environment. Results of simulations are shown for each of the three different turbine configurations when the rotor is operated in oblique flow, in other words when the wind vector is non-perpendicular to the axis of rotation of the rotor, and also when subjected to unsteady wind. The performance of the straight-bladed turbine when it is influenced by the wake of another rotor is also discussed. The capability of the VTM to simulate the flow surrounding vertical-axis wind turbines has been enhanced by a dynamic stall model that was implemented in the course of this research in order to account for the effects of large, transient variations of the angle of attack on the aerodynamic loading on the turbine blades. It is demonstrated that helical blade twist reduces the oscillation of the power coefficient that is an inherent feature of turbines with non-twisted blades. It is also found that the variation in the blade aerodynamic loading that is caused by the continuous variation of the angle of attack on the blades during each revolution is much larger, and thus far more significant, than that which is induced by an unsteady wind or by an interaction with the wake that is produced by another rotor. Furthermore, it is shown that a vertical-axis turbine that is operated in oblique flow can, potentially, produce a higher power coefficient compared to the operation in conditions in which the wind vector is perpendicular to the axis of rotation, when the ratio between the height of the turbine and the radius of the rotor is sufficiently low.