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Novel atomic force microscope (AFM) probes with integrated thin film thermal sensors are presented. Silicon micromachining and high resolution electron beam lithography (EBL) have been used to make batch fabricated, functionalised AFM probes. The AFM tips, situated at the ends of Si3N4 cantilevers, are shaped either as truncated pyramids or sharp triangular asperites. The former gives good thermalisation of the sensor to the specimen for flat specimens whereas the latter gives improved access to highly topographic specimens. Tip radii for the different probes are 1 m and 50 nm respectively. A variety of metal structures have been deposited on the tips using EBL and lift-off to form Au/Pd thermocouples and Pd resistance thermometer/heaters. Sensor dimensions down to 35 nm have been demonstrated. In the case of the sharp triangular tips, holes were etched into parts of the cantilever in order to provide self alignment of the sensor to the tip. On the pyramidal tips it has been shown that multiple sensors can be made on a single tip with good definition and matching between sensors. A conventional AFM was constructed in order to test the micromachined thermal probes. During scans of a photothermal test specimen using improved access thermocouple probes, 80 nm period metal gratings were thermally resolved. This is equivalent to a thermal lateral resolution of 40 nm. Pyramidal tips with a resistance thermometer/heater, which were made for the microscopy and analysis of polymers, have been showed by others to produce high resolution thermal conductivity images. The probes have also been shown to be capable of locally heating a polymer specimen and thermomechanically measuring phase changes in small volumes of material. Also presented here is a study of scanning thermal microscopy of semiconductor structures using a commercial AFM. Included are scans of several specimens using both commercial andthe new micromachined probes. Subsurface images of voids buried under a SiO2 passivation layer were taken. It is shown that contrast caused by thermal conductivity differences in the specimen may be detected at a depth of over 200 nm.

No description available.

As electric utilities move into more competitive generation supply regimes, with limited scope to expand transmission facilities, the optimisation of existing transmission corridors for power transfer becomes of paramount importance. In this scenario, Flexible AC Transmission System (FACTS) technology, which aims at increasing system operation flexibility, appear as an attractive alternative. Many of the ideas upon which the foundations of FACTS rest were conceived some time ago. Nevertheless, FACTS as a single coherent integrated philosophy is a newly developed concept in electrical power systems which has received the backing of the major manufacturers of electrical equipment and utilities around the world. It is looking at ways of capitalising on the new developments taking place in the area of high-voltage and highcurrent power electronics in order to increase the control of the power flows in the high voltage side of the network during both steady state and transient conditions, so as to make the network electronically controllable. In order to examine the applicability and functional specifications of FACTS devices, it is necessary to develop accurate and flexible digital models of these controllers and to upgrade most of the software tools used by planners and operators of electric power systems. The aim of this work is to develop general steady-state models FACTS devices, suitable for the analysis of positive sequence power flows in, large-scale real life electric power systems.Generalised nodal admittance models are developed for the Advance Series Compensator (ASC), Phase Shifter (PS), Static Var Compensator (SVC), Load Tap Changer (LTC) and Unified Power Flow Controller (UPFC). In the case of the ASC, two models are presented, the Variable Series Compensator (VSC) and the Thyristor Controlled Series CapacitorFiring Angle (TCSC-F A). An alternative UPFC model based on the concept of Synchronous Voltage Source (SVS) is also developed. The Interphase Power Controller (IPC) is modelled by combining PSs and VSCs nodal admittance models. The combined solution of the power flow equations pertaining to the FACTS devices models and the power network is described in this thesis. The set of non-linear equations is solved through a Newton-Rapshon technique. In this unified iterative environment, the FACTS device state variables are adjusted automatically together with the nodal network state variables so as to satisfy a specified nodal voltage magnitudes and specified power flows. Guidelines and methods for implementing FACTS devices and their adjustments within the Newton-Rapshon algorithm are described. It is shown that large increments in the adjustments of FACTS devices and nodal network state variables during the backward substitution may dent the algorithm's quadratic convergence. Suitable strategies are given which avoid large changes in these variables and retain the Newton-RapshRapshon method's quadratic convergence. The influence of initial conditions of FACTS devices state variables on the iterative process is investigated. Suitable initialisation guidelines are recommended. Where appropriate, analytical equations are given to assure good initial conditions.

As CMOS device dimensions are being aggressively scaled, the device characteristic must be assessed against fundamental physical limits. Nanoscale device modelling and statistical circuit analysis is needed to provide designer with ability to explore innovative new MOSFET devices as well as understanding the limits of the scaling process. This work introduces a systematic simulation methodology to investigate the impact of intrinsic parameter fluctuation for a novel Ultra-Thin-Body (UTB) Silicon-on-Insulator (SOI) transistor on the corresponding device and circuits. It provides essential link between physical device-level numerical simulation and circuit-level simulation. A systematic analysis of the effects of random discrete dopants, body thickness variations and line edge roughness on a well scaled 10 nm, 7.5 nm and 5 nm channel length UTB-SOI MOSFET is performed. To fully realise the performance benefits of UTB-SOI based SRAM cells a statistical circuit simulation methodology which can fully capture intrinsic parameter fluctuations information into the compact model is developed. The impact of intrinsic parameter fluctuations on the stability and performance of 6T SRAM has been investigated. A comparison with the behaviour of a 6T SRAM based on a conventional 35 nm MOSFET is also presented.

This portfolio thesis documents the work undertaken by the author under the auspices of the Engineering Doctorate (EngD) programme. The research work undertaken was completed at the sponsoring company, A2E Limited. There is a wide range of products and solutions to meet both commercial and personal electronic storage needs. This work documents research and development over a four year period into algorithms, implementations and product development for novel storage solutions for commercial and personal use. The design work and technical and business objectives were guided by the sponsoring company, A4E limited. This portfolio thesis considers the storage market at the start of the project, the commercial and technical aspects relevant to this market place and describes the development and testing of a RAID 6 algorithm in both hardware and software. The key contributions presented in this portfolio thesis include the implementation of the smallest and fastest FPGA based Reed-Solomon RAID 6 hardware accelerator. We also present the first commercial implementation of a Reed-Solomon RAID 6 intellectual property (IP) block. Both the hardware and software implementation are discussed in detail along with the supporting IP blocks and device drivers. Documentation of the product development stages and additional project work carried out to provide an understanding of product development stages and the requirements placed during such work are also examined. the results of testing and implementation are considered and the performance of the proposed solution is considered along with the commercial viability and success of the project.

This thesis will describes how microfabrication techniques can be combined with Atomic Force Microscopy (AFM) to investigate the potential for cellular elasticity to be used as an indicator of cell behaviour and responses to chemical and topographical surface modifications. To this end, a robust and reliable AFM protocol has been developed to take in to account the many changeable parameters encountered when performing live cell indentation measurements. Complimented with traditional molecular biological methods, such as immunofluorescence staining and confocal microscopy, the biomechanical properties and functions of cells have been investigated to see how they respond to simple chemical and topographical cues. Simple surface topographies have frequently been exploited to learn more about cell behaviour and subsequent function however the mechanisms by which the cells senses the surrounding cues and interprets them accordingly has remained somewhat unknown. It is the hypothesis of the work presented here that the arrangement of the internal cytoskeleton as influenced by external factors in responsible for the transmission of tensile strength to the cytoplasm and on to the nuclear membrane. This in turn has the potential to alter transcription within the nucleus ultimately affecting over all cell function.

With the advances in microprocessor technology, control systems are widely seen not only in industry but now also in household appliances and consumer electronics. Among all control schemes developed so far, Proportional plus Integral plus Derivative (PID) control is the most widely adopted in practice. Today, more than 90% of industrial controllers have a built-in PID function. Their wide applications have stimulated and sustained the research and development of PID tuning techniques, patents, software packages and hardware modules. Due to parameter interaction and format variation, tuning a PID controller is not as straightforward as one would have anticipated. Therefore, designing speedy tuning rules should greatly reduce the burden on new installation and ‘time-to-market’ and should also enhance the competitive advantages of the PID system under offer. A multi-objective evolutionary algorithm (MOEA) would be an ideal candidate to conduct the learning and search for multi-objective PID tuning rules. A simple to implement MOEA, termed s-MOEA, is devised and compared with MOEAs developed elsewhere. Extensive study and analysis are performed on metrics for evaluating MOEA performance, so as to help with this comparison and development. As a result, a novel visualisation technique, termed “Distance and Distribution” (DD)” chart, is developed to overcome some of the limitations of existing metrics and visualisation techniques. The DD chart allows a user to view the comparison of multiple sets of high order non-dominated solutions in a two-dimensional space. The capability of DD chart is shown in the comparison process and it is shown to be a useful tool for gathering more in-depth information of an MOEA which is not possible in existing empirical studies. Truly multi-objective global PID tuning rules are then evolved as a result of interfacing the s-MOEA with closed-loop simulations under practical constraints. It takes into account multiple, and often conflicting, objectives such as steady-state accuracy and transient responsiveness against stability and overshoots, as well as tracking performance against load disturbance rejection. These evolved rules are compared against other tuning rules both offline on a set of well-recognised PID benchmark test systems and online on three laboratory systems of different dynamics and transport delays. The results show that the rules significantly outperform all existing tuning rules, with multi-criterion optimality. This is made possible as the evolved rules can cover a delay to time constant ratio from zero to infinity based on first-order plus delay plant models. For second-order plus delay plant models, they can also cover all possible dynamics found in practice.

The rise of photonic integration makes optical code division multiple access (OCDMA) worth revisiting due to its promising role in future all-optical networks. OCDMA has the potential to exploit the surplus bandwidth of optical fibres and to carry over to the optical domain the benefits seen CDMA radio communication systems, such as the effective sharing of the spectrum for multiple network subscribers, and resistance to jamming and eavesdropping. One of the major requirements for the deployment of OCDMA in networks is integration. This thesis presents a research study of integrated OCDMA systems using the AlGaInAs/InP semiconductor material system. This material is considered due to its useful intrinsic properties such as thermal stability, strong electron confinement, and low threshold, making it suitable for fabricating optoelectronic devices. Two bespoke OCDMA systems are considered for integration: coherent temporal phase coding (TPC), and incoherent wavelength-hopping time-spreading (WHTS) OCDMA systems. TPC systems are excellent for high speed communications due to their static en/decoding enabling features. In this research, a 2×2 asymmetric Mach Zehnder interferometer (AMZI) is used to generate a 2-bit phase code, allowing multiplexing for up to four users. A semiconductor mode-locked ring laser is also embedded in the circuit, and using a synchronous mode-locking method, adequate signal en/decoding is achieved. WHTS systems on the other hand fully exploit the spectral and temporal space available in networks by assigning each user with a unique wavelength-time hop sequence for en/decoding data signals. Here, a mode-locked laser array is used with intracavity distributed Bragg reflectors (DBRs) for spectrally tuning each laser, and a 4:1 multimode interference coupler is used to combine the laser signals into a single channel for amplification, modulation and transmission. The integrated system is fully characterised and synchronisation experiments are performed to show the potential for its use in high speed multi-user networks. Mode-locked lasers play an important role in many OCDMA implementations due to their wide spectrum and discrete temporal properties, which can be easily exploited during data en/decoding. Various mode-locked laser devices have been studied during this research with additional embedded components such as intracavity DBRs and phase controllers for precise tuning of the wavelength and pulse repetition frequency. However, the noisy nature of passively operating mode-locked lasers make them prone to high jitter, which can result in high bit error rates. Synchronisation schemes are thereby explored in order to temporally stabilise the pulse oscillations to make them suitable for use in long haul transmission systems. This includes synchronous and hybrid mode-locking, as well as a passive technique using an optical fibre loop to provide phase feedback, which is shown to promote ultralow RF linewidths in mode-locked lasers.

This research presents a more complete flexible model for the Motorised Momentum Exchange Tether (MMET) concept. In order to analyse the vibration aspect of the problem the tether is modelled as a string governed by partial differential equations of motion, with specific static and dynamic boundary conditions and the tether sub-span is flexible and elastic, thereby allowing three dimensional displacements of the motorised tether. The boundary conditions lead to a specific frequency equation and the Eigenvalues from this provide the natural frequencies of the orbiting flexible motorised tether when static, accelerating in spin, and at terminal angular velocity. The rotation matrix is utilized to get the position vectors of the system’s components in an inertial frame. The spatio-temporal coordinates u(x,t), v(x,t) and w(x,t) are transformed to modal coordinates before applying Lagrange’s equations and the pre-selected linear modes are included in generating the equations of motion. The equations of motion contain inertial nonlinearities of cubic order, and these show the potential for intricate intermodal coupling effects. The study of planar and non-planar motions has been carried out and the differences in the modal responses in both motions between the rigid body and flexible model are highlighted and discussed. The dynamics and stability of the flexible MMET is investigated using the dynamical analysis tools for representing the behaviour of the tether system. The study is also includes the engineering side of the MMET by investigating the power requirements of an electric motor located in the central facility of the Motorised Momentum Exchange Tether (MMET). A simulation was run using a specially written computer program to obtain the required minimum power for a typical duty cycle, and also to study the responses for three different operating conditions; before payload release, torque-off and reverse torques conditions for both the propulsion and outrigger system on both circular and elliptical orbits. The differences in the responses when using rigid body and flexible models of MMET are highlighted and discussed in order to look at the sensitivity of the model to the power budget calculations. The study then continues with a comparative study between the MMET and conventional propulsion systems in terms of the energy used specifically for an Earth-Moon return mission for circular and elliptical orbits.