After a brief review of the general properties of superconductors, the difficulties encountered in employing superconducting wires in solenoids are described together with the measures it has been found necessary to take in order to construct coils with satisfactory performance. A comprehensive review of the attempts and proposals in the literature to employ superconductors in rotating energy converters and appraisal of each, is then given. The possibilities of utilizing superconducting winding in conventional types of rotating machines are then examined, and it is shown that probably only the d.c. homopolar machine, the synchronous machine and a toroidal reciprocating generator proposed by Harrowell are suitable for development with superconducting ·windings. The present state of development of superconducting d ,c , homopolar machines is described, and the economic and market prospects for such machines assessed on the basis of the limited data available supplemented by reasonable assumptions. Design procedures for the Harrowell machine are propose, and from these some conclusions are drawn regarding its characteristics. The prospects for superconducting synchronous generators are examined for use in large power systems and shown to be promising, but for aircraft applications it is shown there is no case for mmachines with ratings below 1 MVA at 400 Hz. The inadequacies of existing theories of synchronous machines to cover superconducting types are examined and proposals are put forward to modify the conventional two-axis theory for the superconducting case including parameter evaluation. The experimental work reported covers the design, construction and testing of a.400 Hz rotating armature synchronous generator, with a rating of 50 kVA initially, but capable of being extended to 100 kVA subsequently.

This thesis reports research undertaken to address the deficiencies that existing standardised cryptographic constructs exhibit when securing packet mode wireless communication in WSN. The aim of the research is to devise innovative cryptographic frameworks, which will facilitate design and implementation of light-weight symmetric cryptographic modular constructs. Four cryptographic frameworks have been devised and block cipher based light-weight constructs using the frameworks have been designed and benchmarked against contemporary standard constructs. The constructs introduced in this dissertation, proved to be better suited to providing secure packet mode data communication, in applications utilising wireless networks consisting of characteristically constrained nodes. The four proposed frameworks are: - The Zone-based framework for data packet integrity and authentication security services is proposed and described. The Quicker Block Chaining (QBC) family of message authentication constructs designed using the framework, are shown, via software simulation, to operate with better efficiency (i.e. uses fewer instruction cycles) than similar contemporary standard constructs and with a comparable level of security. - The Hybrid Encryption Mode (HEM) framework for data packet confidentiality security service is proposed and described. The HEM framework facilitated the design of constructs that provide probabilistic, randomising and tweakable encryption. - The Joint Cypher Mode (JCM) framework for authenticated encryption with associated-data (AEAD) security service is proposed and described. The range of constructs designed using the JCM framework, are shown, via software simulation and practical deployment, to Design and Analysis of Light-weight Symmetric Cryptographic Frameworks and Constructs for Secure Packet Mode Wireless Communication operate with better efficiency (i.e. uses fewer instruction cycles) than contemporary standard constructs. - The Joint Authenticated Combined Mode (JACM) framework for authenticate authenticated-encryption with associated-data (AAEAD) security service is proposed and described. The new AAEAD secure packet paradigm addresses a limitation and cryptographic protection failure of the standardised AEAD secure packet paradigm, in communication scenarios when untrustworthy intermediary forwarding nodes are utilised to authenticate and relay packets. The outcomes of the research undertaken are relevant to practitioners and cryptographic engineers that require symmetric cryptographic light-weight constructs for providing secure packet mode communications. It is shown that the resulting light-weight symmetric cryptographic constructs are better suited to providing secure packet mode wireless networked communication.

An overview of quantum phenomena associated with nanoelectronic structures is presented, including resonant tunnelling and mini-band formation in vertical transport devices and channel conductance quantization and interference in lateral devices. The method of construction of these structures is briefly described. Methods of calculating the transmission coefficient are reviewed. In one dimension the transfer matrix method is described and also two derivatives of the approach for circumventing the numerical instability encountered when calculating the wavefunction. In two dimensions an un-coupled matching states method and an asymptotic time dependent method are described. As an alternative to the above methods a coupled network theory is presented for the first time which genuinely represents the 2D time independent electronic wavefunction. Nodes on the network are described by a unitary scattering matrix from which a 2D transfer matrix is derived, connecting lines on the network. The scattering matrix for the whole system is created by combining the 2D scattering matrices for each line, themselves derived from the transfer matrices. The use of the scattering matrix is necessary to ensure numerical stability and current conservation. It is shown that the bandstructure of the network is essential to creating a genuine 2D model whilst at the same time introducing a perturbing influence on the manifestation of physical phenomena. The advantages over other models is the complete absence of restriction on the potential profile considered and no requirement to separate the scalar energy and potential quantities into x and y components. Also no problem with current continuity has been encountered. A major disadvantage is the large time required to calculate wavefunctions compared with the un-coupled matching states method. The network is shown to reproduce the channel conductance quantization recently observed experimentally and is in good agreement with both a 1D analytic model and a 2D un-coupled model. The network is applied to channels containing single and double barriers. In the latter case the resonances are found not to coincide with those predicted by a 1D model. Also the wavefunction on resonance resembles one of the quasi states of the well but with a phase shift. When applied to waveguides involving an interface between channels of different widths the network reveals a tendency for the wavefunction to relax to its original transverse state as it gets further from the interface. This tendency is most pronounced for a tapered junction at low energy (energy of the order of the first transverse eigenvalue). The transmission coefficient for an abrupt junction displays unusual dips above the quantization threshold of the narrow channel. Scattering into higher modes is reduced both by reducing the ratio of channel widths and by reducing the absolute lengths of the device. Finally circle and ring devices are studied, results displaying similarities with Finch's time dependent calculations. In particular scattering into the arms of the ring is observed to be mainly into the first mode if the energy is low and mainly into the third mode if the energy is of the same order as the third transverse eigenvalue of the channel. The tendency to relax into the original transverse state still operates over the whole device.

Peripheral nerve repair outcomes have lagged behind comparable surgical techniques for many decades. A number of advanced approaches have been adopted over the last ten years. In particular the application of electrical stimulation during a repair is of great interest. It is clear that electrical stimulation of regenerating nerve tissue has a great many effects and can improve functional outcomes for patients. This work has focused on developing systems capable of applying accurate electric fields on the microscale within a biodegradable conduit, powered wirelessly. Experiments were conducted in vitro with a view to making progress towards an in vivo implementation. Electrical stimulation was applied to regenerating sensory neurons in vitro, from a rat dorsal root ganglion. Mechanical guidance cues aligned neurons towards different microelectrode configurations in order to record the effect of applied electrical stimulation. This was performed using custom stimulation modules. SU-8 microgrooves and Ti/Au electrodes acted as mechanical and electrical cues respectively. This method was employed to great effect, identifying the effect of a number of electrical stimulation parameters. This led to a stimulation protocol featuring a 1:4 duty cycle, 20 mV amplitude, 100 Hz sinusoidal signal. This produced a number of interesting effects, including neuronal turning and a barrier formation. These results, demonstrated at the cellular level using a custom device and an autonomous stimulation system illustrates progress towards an optimised electrical stimulation waveform for neuronal growth control. A novel transfer printing process was developed to produce patterned gold films on the biodegradable polymer, polycaprolactone. Patterned Au, 400 nm thick, was transferred to a sheet of the polymer, producing a 15 turn, spiral inductor. The inductor was then electroplated to a thickness of 30 μm and wire-bonded. Power and data were transferred wirelessly to the receiver circuit. Receiver circuits, connected to stimulation test modules in planar form, delivered electrical stimulation waveforms to regenerating sensory neurons on polycaprolactone. This stimulation resulted in confinement of the cells between two pairs of electrodes, demonstrating the efficacy of the novel receiver circuits. This was achieved with four electrodes in a twin-barrier configuration. These results illustrate progress towards implantation in vivo, using remotely powered electronics to guide regenerating neurons to their targets with microelectrodes. Sensing cell growth through changes in electrical impedance is a well-documented technique. A receiver inductor has been connected to caco-2 cells in culture. Power was transmitted to the receiver inductor through an inductive link. Changes in the cell-monolayer have been detected at the transmitter output circuit, showing that the impedance changes are of sufficient magnitude to be reflected to the transmitter. Trypsin or EDTA were added to confluent layers of caco-2 cells, detaching them from the surface of the microchannel electrode array. This detachment was seen at the transmitter in the form of transient voltage changes. Data was acquired in using Labview programming and PXI hardware systems. This work illustrates progress towards biodegradable, passive cell sensing inspired by radio frequency identification technology, and electric cell impedance sensing.

The power amplifier is one of the most important and crucial component of the wireless networks due to its high power consumption. For this reason, in the last 20-30 years many scientists from all around the world have addressed the issue of how minimising such power consumption, which means maximising the PA efficiency as well as gain while delivering the expected power and the appropriate linearity for the specified frequency. Nowadays due to the continuous demand of wireless services, PAs with high power-efficiency for the specified narrow band frequency are not enough. Such PAs have to be capable to deliver satisfactory output performance for the wide spectrum frequency. For this reason, the work presented in this thesis is focused around the PA stage and describes a new way to design broadband power amplifiers used in the wireless communication systems. For the first time this work presents what have been termed “Continuous Modes”. It is known that for delivering high efficiency states, output high harmonic impedances must be taken into account. However, the knowledge of where such harmonic terminations should be once found the singular optimum fundamental load would deliver the high efficiency condition but will not reveal information in terms of bandwidth. In this work it is demonstrated that if varying the reactive part of the fundamental impedance from the optimum condition and adjusting reactively the high harmonic terminations in accordance with the Continuous theory applied to the different PA classes, a new “Design Space” where the output performance remains theoretically constant can be achieved. Furthermore, varying both reactively and resistively the fundamental load and again adjusting the magnitude and phase of the high harmonic terminations a yet wider design space would be revealed with the output performance slightly degraded from the optimum condition but still giving satisfactory performance. The degradation of such performance is balanced to the fact that now new alternative solutions are revealed allowing more flexibility in the PA design. Now the PA designer can decide which new impedances to target if designing narrow band PAs or he can decide to target more solutions for which broadband PAs can be realised. Broadband Continuous PAs - Vincenzo Carrubba - xii The research presented in this thesis shows the theoretical Continuous Mode theory applied to the various PA classes supported by experimental measurement results using the Waveform Engineering Time Domain Active Envelope Load-Pull system developed at Cardiff University applied to different transistors technology and sizes. Besides, a Continuous Class-FV PA delivering around 10.5 W of average power, 11 dB of average gain and 65-80% of drain efficiency for an octave bandwidth between 0.55 GHz and 1.1 GHz has been designed and realised.

This thesis contributes the research and development of novel receiver optimization approaches conducted in ultra-wide bandwidth (UWB) systems. The ultimate goal of the improved receiver technology is to simplify the receiver structures at the cost of a tolerable performance degradation or improve the receiver performances at the cost of a tolerable complexity. Recently, UWB technology has become more and more attractive due to its increased performance. An advanced scheme that can provide a further improvement is strongly recommended and highly demanded. This research project focuses on the design of outstanding receivers suitable for the UWB system with transmitted-reference signaling. Two types of improved receivers are investigated. The first one is based on the optimization of inter-pulse time delay Td in the traditional transmitted-reference receivers where one data pulse is transmitted Td seconds delay after one reference pulse in a bit duration. The second one is based on the joint optimization of the number of reference symbols and the integration interval length in the generalized transmitted-reference receivers where Nd data symbols are transmitted after Nr reference symbols in a data packet. For both improved receivers, simulation and theoretical approaches are used to provide the optimization results. The numerical results show that the improved receivers by using different optimization approaches outperform the non-improved receivers significantly for most practical cases. An up to 4.2dB performance improvement can be achieved consequently. The principal conclusion from this thesis is that all the optimization schemes presented herein can be successfully applied to the design of receivers in the UWB transmitted-reference systems that the data decision can be obtained by thresholding the correlator output of the reference information with the data information.

The challenge of creating a new environment of links for wireless infrared and optical local area networks (LANs) is driving new innovations in the design of optical transceivers. This thesis is concerned with a systematic approach to the design of receivers for indoor optical wireless communication. In particular, it is concerned with how to offer bandwidth adjustment capability in a receiver according to the dynamic service quality of the incoming signals. Another part of the discussion of the thesis is how one can properly choose the front-end preamplifier and biasing circuitry for the photodetector. Also, comparison is made between different types of amplifier, and the methods of bandwidth enhancement. The designs of six different techniques of integrating transimpedance amplifiers, with photodetectors to adapt an adjustable bandwidth control receiver are discussed. The proposed topologies provide an adjustable range of bandwidths for different frequency ranges, typically between 52Hz to 115MHz. The composite technique designs were used to incorporate into a system with an automatic gain control to study its effect, on an optical wireless receiver which had bandwidth adjustment and automatic gain adjustment. Theoretical analysis of noise performance for all the designed circuits is also presented. The theory and design of obstacles of indoor optical wireless receiver delivery, in addition to techniques for mitigating these effects, are discussed. This shows that infrared is a viable alternative to ratio for certain applications.

One of the main trend in the development of high power electric machines (motors, generators) is to replace the magnetic components with superconducting wires, this inevitably leads to a critical requirement from the industry (Converteam) to operate power devices at cryogenic temperatures. However, the current understanding of the behaviour power devices at cryogenic temperatures is limited, especially below the liquid nitrogen temperature of 77 K. This is a problem since most of the superconducting wires operate at temperatures below 77 K. Furthermore, it is uncertain which device type is better, if at all suited to cryogenic operation. In order to answer this, a thorough analysis of the known cryogenic behaviour of all the generic power devices was performed, including the physical behaviour of silicon at cryogenic temperatures. It is concluded that the power MOSFET is the best likely candidate for cryogenic operation. To understand the cryogenic behaviour of silicon power MOSFETs especially between the temperatures of 20 K and 100 K, a cryogenic measurement system was built to characterise different types of power MOSFETs. All the measured power MOSFETs exhibited large improvement in on-state resistance down to 50 K and non-linear degradation of breakdown voltages with lower temperatures. Various behaviour was observed below 50 K including carrier freeze-out, electric field dependent ionisation of free charge carriers and large variations in on-state resistance between identical devices. Several power Schottky diodes were also characterised and all exhibited merged PiN Schottky diode behaviour at cryogenic temperatures. Non-silicon devices such as silicon carbide power MOSFETs and gallium nitride HEMTs were also measured. Silicon carbide exhibited no improvements at cryogenic temperatures, whereas gallium nitride HEMTs may prove to be the best power device to be utilised in future cryogenic applications. Since unusual behaviour was observed in power MOSFETs below 50 K, an attempt was made to explain these phenomena using theoretical equations of semiconductor physics and analytical models of power MOSFETs. The author suggested that careful control of the dopant concentration at the accumulation region below the oxide gate is required to improve the power MOSFET operations below 50 K. Moreover, the super-junction power MOSFETs could be optimised for better cryogenic operation. It is the intention of this work to demonstrate the benefits of power MOSFET cryogenic operation in a realistic industrial application. A demonstration model was designed and simulated, this circuit uses a back-to-back power MOSFETs configuration to control the freewheeling current flowing through a high temperature superconducting coil. The electrical and thermal design of the model has been described, simulated and presented in this work.

With the development of mass spectrometry (MS) instruments starting in the late 19th century, more and more research emphasis has been put on MS related subjects, especially the instrumentation and its applications. Instrumentation research has led modern mass spectrometers into a new era where the MS performance, such as resolving power and mass accuracy, is close to its theoretical limit. Such advanced performance releases more opportunities for scientists to conduct analytical research that could not be performed before. This thesis reviews general MS history and some of the important milestones, followed by introductions to ion cyclotron resonance (ICR) technique and quadrupole operation. Existing electronic designs, such as Fourier-transform ion cyclotron resonance (FT-ICR) preamplifiers (for ion signal detection) and radio-frequency (RF) oscillators (for ion transportation/filtering) are reviewed. Then the potential scope for improvement is discussed. Two new FT-ICR preamplifiers are reported; both preamplifiers operate at room temperature. The first preamplifier uses an operational amplifier (op amp) in a transimpedance configuration. When a 18-k feedback resistor is used, this preamplifier delivers a transimpedance of about 85 dB , and an input current noise spectral density of around 1 pA/ p Hz. The total power consumption of this circuit is around 310 mW when tested on the bench. This preamplifier has a bandwidth of fi3 kHz to 10 MHz, which corresponds to the mass-to-charge ratio, m/z, of approximately 18 to 61k at 12 T for FT-ICR MS. The transimpedance and the bandwidth can be adjusted by replacing passive components such as the feedback resistor and capacitor. The feedback and bandwidth limitation of the circuit is also discussed. When using an 0402 type surface mount resistor, the maximum possible transimpedance, without sacrificing its bandwidth, is approximated to 5.3 M . Under this condition, the preamplifier is estimated to be able to detect ~110 charges. The second preamplifier employs a single-transistor design using a different feedback arrangement, a T-shaped feedback network. Such a feedback system allows ~100-fold less feedback resistance at a given transimpedance, hence preserving bandwidth, which is beneficial to applications demanding high gain. The single-transistor preamplifier yields a low power consumption of ~5.7 mW, and a transimpedance of 80 dB in the frequency range between 1 kHz and 1 MHz (m/z of around 180 to 180k for a 12-T FT-ICR system). In trading noise performance for higher transimpedance, an alternative preamplifier design has also been presented with a transimpedance of 120 dB in the same frequency range. The previously reported room-temperature FT-ICR preamplifier had a voltage gain of about 25, a bandwidth of around 1 MHz when bench tested, and a voltage noise spectral density of ~7.4 nV/ p Hz. The bandwidth performance when connecting this preamplifier to an ICR cell has not been reported. However, from the transimpedance theory, the transimpedance preamplifiers reported in this work will have a bandwidth wider by a factor of the open-loop gain of the amplifier. In a separate development, an oscillator is proposed as a power supply for a quadrupole mass filter in a mass spectrometer system. It targets a stabilized output frequency, and a feedback control for output amplitude stabilization. The newly designed circuit has a very stable output frequency at 1 MHz, with a frequency tolerance of 15 ppm specified by the crystal oscillator datasheet. Within this circuit, an automatic gain control (AGC) unit is built for output amplitude stabilisation. A new transformer design is also proposed. The dimension of the quadrupole being used as a mass filter will be determined in the future. This circuit (in particular the transformer and the quadrupole connection/mounting device) will be finalised after the design of the quadrupole. Finally, this thesis concludes with a discussion between the gain and the noise performance of an FT-ICR preamplifier. A brief analysis about the correlation between the gain, cyclotron frequency, and input capacitance is performed. Future work is also suggested for extending this research.

Cognitive radio has been proposed as a promising solution to the conflict between the spectrum scarcity and spectrum under-utilization. As the demand increases for wireless communication services, cognitive radio technology attracts huge attention from both commercial industries and academic researches. The purpose of this thesis is to provide an analytical evaluation of the cognitive radio system performance while taking into consideration of some realistic conditions. Several problems are investigated in this thesis. First, by adopting a dynamic primary user traffic model with one primary user occupancy status change and exponentially distributed channel holding times, its effect on the cognitive radio system performance is evaluated. In the evaluation, the sensing-throughput tradeoff of the cognitive radio is used as the examination criteria, while energy detection is applied during the spectrum sensing. The thesis then takes the investigation further by establishing a primary user multiple changes traffic model which considers multiple primary user occupancy status changes and any reasonable channel holding time distributions. The effect of the primary user multiple changes traffic on the spectrum sensing performance is investigated while the channel holding times are assumed to be exponential, Gamma, Erlang and log-normal distributed. The analytical evaluation of cognitive radio is also carried out from the secondary user transmission perspective, where the performance of the adaptive modulation in cognitive radio system is investigated. The effect of the cognitive radio distinctive features on the performance of both the adaptive continuous rate scheme and the adaptive discrete rate scheme of the adaptive modulation are examined. The BER performance and the link spectral efficiency performance are derived for both schemes. A novel frame structure where the spectrum sensing is performed by using the recovered received secondary frames is also evaluated in this thesis. A realistic scenario which considers the secondary user signal decoding errors is examined for the novel structure, while an ideal upper bound performance is given when the decoding process is assumed perfect. By extending the system to include multiple consecutive secondary frames, the performance of the novel structure is compared to the performance of the traditional frame structure proposed by the IEEE 802.22 WRAN standard. The effect of the primary user multiple changes traffic is also examined for the novel structure. Several major findings are made from the analytical evaluations presented in this thesis. Through numerical examinations, it was shown that, first, the dynamic primary user traffic degrades the performance of cognitive radio systems. Second, the degree of the performance degradation of the cognitive radio systems is related to the number of primary user status changes and the primary user traffic intensity. Different primary user channel holding times distributions also lead to different sensitivities of the system performance to the primary user traffic. Third, cognitive radio distinctive features degrades the performance of the adaptive modulation. When the novel structure is applied for cognitive radio, a higher secondary achievable throughput can be obtained with a limited saturation threshold.