The growing demands for electrical capacity on future more electric aircraft (MEA) has led the engine-based generators to increase in size. Many manufacturers and researchers have a strong interest in developing fuel cells for aerospace applications due to their advantage of high efficiency and their use as a medium for clean energy resources. A particular interest is in using fuel cells within the Auxiliary Power Unit (APU) - a function that is currently provided by an additional gas turbine in most aircraft. Their integration into aircraft systems is not straightforward. A particular challenge, which this thesis addresses, is the provision of a suitable power conversion system which is able to interface the fuel cell to the aircraft electrical system – taking account of the complex electrical characteristics of the fuel cell and the demanding requirements of the aircraft electrical network. The interleaved boost converter with coupled inductors (IBCI) is one of the many converters that is promising for fuel cell applications because it has low input current ripple and a high step-up voltage gain. It comprises a current doubler circuit, voltage doubler rectifier, coupled inductor and active clamp. The proposed converter is an extended version of the single phase to multiphase IBCI converter using interleaving techniques. The input stage of the converter is a coupled inductor which connected to a half-bridge configuration and an active clamp. The output side is a voltage doubler rectifier. A detailed analysis of the converter and associated modelling are presented. The design and construction of a prototype converter is presented with a particular focus on ensuring operability of the converter over the entire fuel cell characteristic range as well as achieving high efficiency at nominal load. A laboratory-scale (1/10) prototype of a nominal full-scale converter was built to verify the feasibility of the proposed converter topology. Good agreement between the experimental results and the simulation results has been demonstrated, which validates the converter design, modelling, and effectiveness of the efficiency evaluation approximations.

This dissertation reports the research work that was conducted to propose a non-volatile architecture for FPGA using resistive switching devices. This is achieved by designing a Configurable Memristive Logic Block (CMLB). The CMLB comprises of memristive logic cells (MLC) interconnected to each other using memristive switch matrices. In the MLC, novel memristive D flip-flop (MDFF), 6-bit non-volatile look-up table (NVLUT), and CMOS-based multiplexers are used. Other than the MDFF, a non-volatile D-latch (NVDL) was also designed. The MDFF and the NVDL are proposed to replace CMOS-based D flip-flops and D-latches to improve energy consumption. The CMLB shows a reduction of 8.6% of device area and 1.094 times lesser critical path delay against the SRAM-based FPGA architecture. Against similar CMOS-based circuits, the MDFF provides switching speed of 1.08 times faster; the NVLUT reduces power consumption by 6.25nW and improves device area by 128 transistors; while the memristive logic cells reduce overall device area by 60.416μm2. The NVLUT is constructed using novel 2TG1M memory cells, which has the fastest switching times of 12.14ns, compared to other similar memristive memory cells. This is due to the usage of transmission gates which improves voltage transfer from input to the memristor. The novel 2TG1M memory cell also has lower energy consumption than the CMOS-based 6T SRAM cell. The memristive-based switch matrices that interconnects the MLCs together comprises of novel 7T1M SRAM cells, which has the lowest energy-delay-area-product value of 1.61 among other memristive SRAM cells. Two memristive logic gates (MLG) were also designed (OR and AND), that introduces non-volatility into conventional logic gates. All the above circuits and design simulations were performed on an enhanced SPICE memristor model, which was improved from a previously published memristor model. The previously published memristor model was fault to not be in good agreement with memristor theory and the physical model of memristors. Therefore, the enhanced SPICE memristor model provides a memristor model which is in good agreement with the memristor theory and the physical model of memristors, which is used throughout this research work.

The rise and consolidation of Additive Manufacturing (AM) as a technology has made possible the fabrication of highly customised and complex products in almost every industry. This not only allows the creation of objects that were impossible just a few decades ago but also facilitates the production of small runs of products at a reasonable cost, which reduces the design-prototyping cycles and boosts product innovation. However, to produce truly functional parts it is desirable for these systems to be able to deposit multiple complex materials in a single process to locally embed controllable properties such as electrical conductivity or sensing capabilities into the produced geometries. Consequently, a review of current AM technologies capable of depositing conductive materials is performed in this PhD and discussed to find the most suitable approaches. Similarly, existing multi-material set-ups are studied to find limitations and common practices to create a system that is capable of fulfilling the objectives of this work. Piezo-activated inkjet printing (PIJ) is identified as an appropriate technology for multi-material applications due to its non-contact nature, high spatial resolution, capability of mixing and digitally grading materials and simple scale-up of the process. Furthermore, in the last decade it has been shown that jetting can be used for the accurate deposition of a wide range of functional materials. However, upon detailed review of this method, the limitations that it imposes on the compositions of the inks are identified as its main drawback. Specifically, the solid content and molecular weight of the fluids that can be jetted are restricted by the viscosity of the final ink, typically under 40 mPa·s. This is problematic in the case of jetting conductive materials, since it forces the solid content to be very low, therefore yielding very thin and often inhomogeneous layers. Additionally, all the organic components on the inks added to facilitate its ejection need to be removed, which typically means longer and more aggressive post-processes before rendering the printed tracks conductive. For this reason, drop-on-demand micro-dispensing valves were chosen as a high viscosity jetting (HVJ) approach in this work, with the intention of assessing their capability as a suitable tool for multi-material AM of functional inks. However, since their resolution and speed are lower than conventional inkjet, a hybrid approach is presented including micro-dispensing valves and inkjet printheads capable of depositing a wide range of viscosities in a single process. A comprehensive description of the hybrid set-up is given, discussing its main elements including the printing heads, the custom design printer assembly, the ultraviolet (UV) and infrared (IR) lamps installed for in-situ processing, the monitoring system and the set-up to measure the evolution of the electrical resistance in printed tracks in real time during post-processing. Additionally, the printing strategy and process flow is discussed. The investigated set-up was used to study the printability and performance of several functional materials ranging from UV-curable polymers to conductive formulations such as carbon paint, a silver nanoparticle-based paste and a dispersion of PEDOT:PSS. Each material was thoroughly characterised prior to printing with a special focus on viscosity. Their drop formation and deposition processes were studied at different printing settings using high speed imaging and footprint analysis of the deposited drops. These tests were used to obtain sets of working parameters that allow reliable printing and were used to produce 2D patterns with different resolutions to find the drop spacing that results in flat homogeneous films. Later, these films were post-treated according to the requirements of each material and multilayer structures were produced and analysed with an optical profilometer. The cross-section of these 3D tracks was used together with the measured resistance to obtain the electric conductivity of the materials under the printing conditions used. Finally, the accumulated information during the previous stages of printing was used to produce 3D multi-material demonstrators with incorporated conductive tracks, electric components and electroluminescent elements. These proof-of-concept samples were used to discuss limitations of the approach and showcase future possibilities of the system.

Attaching micro-channel heat sinks operating under flow boiling conditions on heat sources of electronic components is an efficient cooling technique which still requires further improvements of designs. When developing this system, the efficient heat transfer performance is essential, however, this development often entangles with difficulties. The difficulties arise as existing prediction approaches are underdeveloped and inadequate to perform the accurate prediction in wide ranges of operating conditions. This inadequacy persists due to incomplete discoveries of involved mechanisms that involve fluid and dynamics for the heat transfer during the flow boiling. Also, the mechanisms involved in the flow boiling process are complicated, hindering the development of more reliable approaches. By addressing this issue, this study explores and investigates the relating mechanisms. The mechanisms of fluids during the flow boiling of subcooled liquids in micro-channel heat sinks immediately before and during the nucleation of first bubbles were explored in this study. This study then addressed the mechanisms of heat transfer enhancement of flow boiling. Later, this study repeated with different substrate materials of micro-channel heat sinks and working fluids. This study serves the purpose to better understand the involved mechanisms during the flow boiling of subcooled liquids in micro-channel heat sinks for the development of more reliable approaches to predict the heat transfer. This study regarding the mechanisms during the flow boiling in micro-channel heat sinks implemented the numerical model associated with the Volume of Fluid (VOF) in which corresponding governing equations were solved using a computational fluid dynamics (CFD). In this model, computational domains of micro-channel heat sinks in three dimensions that include the sub-domains of solids and fluid were created to consider the conjugate heat transfer for better estimation of data. The data collected in this study were from operating parameters of heat flux, mass flux, and inlet temperature of the micro-channel at 500-3197 kW/m2, 115-389 kg/m2 s, and 23-53°C, respectively. The micro-channel heat sinks operated at the atmospheric pressure, and the corresponding substrate materials chosen were steel, silicon, aluminium and copper, and working fluids selected were water and ethanol. The numerical results agree well with the experimental data from the previous study. The results show that although the bubble nucleation is absent, the heat transfer mechanisms in micro-channels possesses the nucleate boiling characteristic involving the transient conduction with the existence of the phase change process. The heat transfer mechanisms from the phase change process with the incomplete evaporation induce the ascending and descending flows and liquid-vapour mixture on the heating surfaces. From the results, four different modes of heat transfer mechanisms from the phase change process associated with ascending and descending flows and liquid vapour mixture become apparent. The ascending and descending flows on the heating surfaces appear with local increases of pressure gradients near to the heating surfaces facilitating the heat transfer enhancement due to phase change. On the other hand, the liquid-vapour mixture produced from the phase change process impeding the heat transfer. In overall, the heat transfer enhancement due to the phase change at the side surfaces in the micro-channel is more extensive as compared to the bottom surface for each condition tested in this study. Meanwhile, the amount of the liquid-vapour mixture accumulating on the bottom surface is more massive as compared to the side surfaces, leading to the impedance of the heat transfer. These heat transfer mechanisms also persist during flow boiling in micro-channels. The heat transfer enhancement due to phase change from the side and bottom surfaces also varies when employing different operating conditions before and during flow boiling. This study provides better insights for researchers and designers in industries regarding the local mechanisms for the heat transfer during the flow boiling in micro-channel heat sinks. These understandings assist the researchers to develop the more reliable prediction methods to design new and better heat transfer performance of micro-channel heat sinks and avoid repeating experiments which are costly and tedious in procedures.

M.Tech. (Electrical Engineering) / Please refer to full text for abstract

Memory design plays an important role in modern computer technology in regard to overall performance and reliability. Prior memory technologies, including magneticcore memory, hard disk drives, DRAM, SRAM have limitations in regard to bit density, IC integration, power efficiency, and physical size, respectively. To address these limitations we propose to develop a magnetic graphene random access memory (MGRAM) utilizing graphene Hall effect, which takes advantage of the inherent reliability of magnetic memory and superior electrical properties of graphene (high carrier mobility, zero-band gap, high Hall sensitivity). As the graphene magnetic memory device will be integrated with a CMOS ASIC design an analog circuit model for the MGRAM cell is necessary and important. In this study the electrical circuit model is developed utilizing the analog circuit modeling language Verilog-A. The electrical circuit model characterizes the graphene electrical properties and the ferromagnetic core magnetic properties that retains the bit-state value. MGRAM device simulations studying varying coil width, height, radius, contact pad configuration, graphene shape, is performed with the MagOasis Magsimus tool to evaluate the device performance. Model results show a maximum Hall effect voltage of 100mV for a bias current of 50uA with a 1 Tesla magnetic field, and a writing speed of 6-9ns for setting the magnetic state. These results will be validated against the circuit hardware measurement and will be used for model refinement.

M.Ing. / A constant demand exists for ever decreasing size in switch mode supplies. The first step has been the introduction of resonant mode converters. Such converters typically consist of a resonant tank, a transformer and an input or output filter. The soft-switching characteristics of these converters allow an order of magnitude higher frequency, thus reducing the size of the reactive components. The next logical step towards a smaller package is introduced, namely the electromagnetic integration of the resonant tank and, if possible, the transformer into a single component, which; not only saves mass and volume, but can also reduce manufacturing costs. The particular converter investigated is the well known series resonant converter. It is shown that the necessary capacitance can be achieved by using a bifilar primary and the leakage inductance of the transformer replaces the physical inductor. Simulation of a suitable distributed circuit network indicates the same frequency domain characteristics and time domain waveforms for both the integrated component, and the discrete inductor, capacitor an transformer in series. Possible configurations for the integrated LCT-component are proposed, and theoretical analysis predicts an operating frequency in the MHZ region. Notwithstanding the complicated manufacturing, results show An integrated LCT-component, applied in a prototype 1 MHz power supply, with an efficiency of approximately 90 %. If manufacturing of the LCT-component allows an acceptable dimension and an acceptable resonant frequency, this can be a very competitive technology.

Ground Penetrating Radar (GPR) is widely used in area of geologic exploration, hidden stationary subject detection and quality inspection on various infrastructures. The pulse generator, which offers very accurate timing information, is the most cardinal component in GPR systems. It is easy to design a pulse generator which produces pulse with pre-settled peak value and pulse width in nanosecond scale. However, since the system is working in complicated environments, various pulses in different pulse widths and amplitudes are needed. In this background, pulse generators in tunability and stability are precious in value and universal in use. Indeed, a few adaptive high voltage pulse signal generators in UWB circuit level have been developed. A pulse generator with tunable pulse width and controllable voltage amplitude is proposed under these demands. The proposed circuit implementation combines System-On-Chip (SOC) design with Printed Circuit Board (PCB) design because we intend to realize modulation separately. We also design an easy input console named Binary Input Array in the research to realize control simplicity. Furthermore, we employ mathematical model to optimize parameters in each component in order to have an improved performance. Simulation data are obtained from Cadence Virtuoso and OrCAD Capture.

The aim of this thesis is to undertake a life cycle analysis to identify the environmental impact of using graphene to manufacture supercapacitors. It was part of a larger project to develop supercapacitors using graphene in place of activated carbon. The first part of this work focuses on production of graphene in the laboratory. Data were directly measured in different laboratories to perform a comparative life cycle analysis in order to evaluate the environmental performance of several graphene synthesis methods including graphite electrochemical exfoliation, graphite chemical oxidation with subsequent chemical or thermal reduction and chemical vapour deposition. One electrochemical exfoliation technique, one chemical oxidation followed by two different reduction routes were selected on the base of their environmental performance and their measured specific capacitance and used as electrode materials for supercapacitors. The second part of the thesis is a comparative life cycle assessment involving three supercapacitors having the electrodes made of graphene synthesised via the three shortlisted production routes and one state of the art activated carbon based supercapacitor commercially available. A commercial-scale graphene production process is simulated using a process simulation tool in order to minimise the process inefficiencies inherent to laboratory processes and to compare it with a commercial-scale activated carbon production process. The results showed a large reduction of the graphene environmental impact of around 50% in most of the environmental impact categories analysed but also proved that the activated carbon supercapacitor is currently the technology with the lowest impact for all categories. They also showed that graphene production needs more research to improve its efficiency and efficacy as it is the operation with the highest environmental impact in the supercapacitor manufacturing for most of the analysed impact categories. In the third part of this study the use-phase and end-of-life of supercapacitors is evaluated in which the supercapacitors are used to power a car door mirror and are finally recycled. The results showed that over the lifetime of a vehicle (150,000 km), the graphene based supercapacitors have a lower impact (10% less) during the use-phase as they are lighter. The recycling process is also simulated to be scaled up to a commercial-scale with minimised heat losses for both graphene and activated carbon based supercapacitors. Recycling proved to be the key to reduce the environmental impact of the graphene supercapacitor. As graphene proved to be the most problematic material for the environment and the recycled graphene proved to be of a quality similar to pristine material, its recovery generates an environmental credit that is 90% of the production burden for all categories by displacing the production of new graphene for polymer reinforcement applications. Sensitivity analysis is performed and various scenarios generated to evaluate potential variations in specific capacitance of all active materials and subsequently the impact of these variations on the manufacture of supercapacitors. The results are normalised and weighted according to the latest EU requirements. Aggregating the weighted results proved that the activated carbon and the graphene based supercapacitors could have similar impacts. This is a very encouraging result considering that the graphene synthesis process is still at its infancy while the activated carbon production is a well-established industrial process. When a more efficient graphene production can be industrialised, graphene supercapacitors will have the potential to become the future technology with the lowest environmental impact.

The objective of this work is to design, simulate and synthesize a dynamic space controller system. The concept of space allocation and management can be applied to more than physical space. It may also be taken in the contexts of memory, network or bus management. The management and allocation of any space depends mostly on the twin factors of demand and availability. Time, the size and amount of space available, as well as the number of requests for the spaces, must also be considered. The proposed design has the capability to monitor multiple spaces for vacancies, length of time occupied and to dynamically track the number and location of available spaces. This system is easily programmed to adapt to the user’s application and is modular in design in order to facilitate expansion. The specific problem addressed in this work is a parking lot controller.