High power impulse magnetron sputtering (HiPIMS) is a plasma-based thin film deposition technique in which extremely high power pulses are applied to a conventional magnetron sputtering source. As a result, the plasma density in HiPIMS discharges is considerably increased up to 1E19 per cubic metre, about three orders of magnitude higher than that in conventional direct current magnetron sputtering (DCMS) discharges. Hence the vapour of the sputtered species becomes highly ionised, leading to remarkable improvement in the microstructure and the properties of depositing films. To better control the deposition process, it is important to gain insights into the properties and the dynamics of the HiPIMS plasmas. This thesis is associated with the investigations on HiPIMS plasmas using a number of electrical diagnostic tools including a Langmuir probe, a retarding field energy analyser and a gridded quartz crystal microbalance. It was shown, using a Langmuir probe analysis, that there are three distinct groups of electrons generated during first the 4 microseconds of the HiPIMS pulse. These electrons are super-thermal or beam-like electrons with effective temperatures of up to 100 eV, hot electrons with temperatures up to 7 eV and cold electrons with temperatures < 1 eV. As time progresses, however, these electrons develop into single-temperature Maxwellian electrons. Using the retarding field energy analyser located at typical substrate positions, it was found that ions travel to a grounded substrate with an average energy of up to 10 eV during 20-40 microseconds into the HiPIMS pulse, and with an energy of 3-5 eV for the rest of the pulse. Ions escaping to the side of the discharge axis are also investigated using the movable and rotatable retarding field analyser. It was found that ions, circulating with a similar direction as the electron ExB drift in the magnetised region, are able to azimuthally escape from the discharge with a mean velocity of 8E3 metre per second, unless there are collisions with residual gases. Together with the knowledge of radial electric field, determined from plasma potential, the equations of circular motion of an ion fluid element have been solved numerically. Using a biased quartz crystal microbalance in combination with a gridded electrode, the ionised metal flux fraction in a HiPIMS discharge has been investigated. The average discharge power was varied from 0.3 to 1.3 kW and, irrespective of the power control method used, an associated decrease in the flux fraction (from 50 % to 30 %) was observed. The mechanisms responsible for this decrease in the time-averaged flux fraction of metal ions are associated with the probability of ionisation of the sputtered species and the effect of the ions returning to the target. Finally, a technique of the superposition of a dc pre-ioniser and a HiPIMS power supply is proposed to operate a HiPIMS discharge at a pressure down to 0.08 Pa. The pre-ioniser provides a background plasma with a density of 1E15 per cubic metre to assist the HiPIMS build-up at the low-pressure range. Using an energy-resolved mass spectrometer, it was demonstrated that the average energy and charge state of ions can be enhanced in the low-pressure operation.

Most terahertz (THz) time-domain (pulsed) imaging experiments that have been performed by raster scanning the object relative to a focused THz beam require minutes or even hours to acquire a complete image. This slow image acquisition is a major limiting factor for real-time applications. Other systems using focal plane detector arrays can acquire images in real-time, but they are too expensive or are limited by low sensitivity in the THz range. More importantly, such systems cannot provide spectroscopic information of the sample. To develop faster and more efficient THz time-domain (pulsed) imaging systems, this research used random projection approach to reconstruct THz images from the synthetic and real-world THz data based on the concept of compressed/compressive sensing/sampling (CS). Compared with conventional THz time-domain (pulsed) imaging, no raster scanning of the object is required. The simulation results demonstrated that CS has great potential for real-time THz imaging systems because its use can dramatically reduce the number of measurements in such systems. We then implemented two different CS-THz systems based on the random projection method. One is a compressive THz time-domain (pulsed) spectroscopic imaging system using a set of independent optimized masks. A single-point THz detector, together with a set of 40 optimized two-dimensional binary masks, was used to measure the THz waveforms transmitted through a sample. THz time- and frequency-domain images of the sample comprising 20×20 pixels were subsequently reconstructed. This demonstrated that both the spatial distribution and the spectral characteristics of a sample can be obtained by this means. Compared with conventional THz time-domain (pulsed) imaging, ten times fewer THz spectra need to be taken. In order to further speed up the image acquisition and reconstruction process, another hardware implementation - a single rotating mask (i.e., the spinning disk) with random binary patterns - was utilized to spatially modulate a collimated THz. After propagating through the sample, the THz beam was measured using a single detector, and a THz image was subsequently reconstructed using the CS approach. This demonstrated that a 32×32 pixel image could be obtained from 160 to 240 measurements. This spinning disk configuration allows the use of an electric motor to rotate the spinning disk, thus enabling the experiment to be performed automatically and continuously. To the best of our knowledge, this is the first experimental implementation of a spinning disk configuration for high speed compressive image acquisition. A three-dimensional (3D) joint reconstruction approach was developed to reconstruct THz images from random/incomplete subsets of THz data. Such a random sampling method provides a fast THz imaging acquisition and also simplifies the current THz imaging hardware implementation. The core idea is extended in image inpainting to the case of 3D data. Our main objective is to exploit both spatial and spectral/temporal information for recovering the missing samples. It has been shown that this approach has superiority over the case where the spectral/temporal images are treated independently. We first proposed to learn a spatio-spectral/temporal dictionary from a subset of available training data. Using this dictionary, the THz images can then be jointly recovered from an incomplete set of observations. The simulation results using the measured THz image data confirm that this 3D joint reconstruction approach also provides a significant improvement over the existing THz imaging methods.

HiPIMS discharges operated with a titanium and an aluminium-doped zinc target sputtered with the working gas argon were investigated by means of optical 2d-imaging in combination with Abel-inversion. By using optical bandpass filters, the spatial and temporal evolution of the plasma-induced emission of argon atoms and ions and metal atoms and ions were studied. The discharge ignition was found to be accompanied by an intensity maximum observed remote from the target, followed by an asymmetric intensity profile. During the stage of high discharge current, the intensity distribution indicates strong rarefaction of the working gas, efficient ionisation of the sputtered particles above the target and a wider sputter distribution. The off-time is characterised by an initial drop of the intensity by 4 - 6 orders of magnitude and a transition from electron-impact excitation to excitation by electron-electron-ion recombination. Decay constants in the order of 1 ms and the spatial distribution of the emission suggest the loss of electrons and ions due to ambipolar diffusion across the magnetic field. Plasma potential measurements by means of emissive probe revealed strongly negative space potentials of up to -300 V and electric fields in the order of 10000 V/m during discharge ignition, caused by strong charge separation due to the extended sheath. The plasma potential increases to a stable level of more than -25 V during the second half of the discharge pulse, while the electric field is largely reduced to maximal 1500 V/m. It was found that the space potential is consistently 5 V lower when the substrate is kept floating compared to a grounded substrate, which can be explained by the reduced electron loss rate to the substrate due to the potential barrier. This is confirmed by spatially resolved Langmuir probe measurements, showing a density maximum of 1019 m-3 in the confined plasma zone, and an increased density in the vicinity of the floating substrate of 1.3 × �1018 m-3 compared to 0.8 × �1018 m-3 for a grounded substrate. The electron temperature was found to be spatially uniform ranging from 1 eV to 3 eV. A quasi-continuous transport model for sputtered particles confirmed the high degree of ionisation of the sputtered particles of about 90 % and revealed a return probability for titanium ions to the target of 80 % for Ti+ and 96 % for Ti2+. Varying the force caused by a modified two-stream instability [1], showed an increasing sideway defletion of ions also increasing the kinetic energy observed for these particles. The spatial distribution of the relative density confirmed efficient ionisation of sputtered particles in the dense plasma zone adjacent to the target. Average azimuthal velocities of the drifting ion fluid of 3�000 m/s for Ti+ and 7�000 m/s for Ti2+ were obtained.

The requirements of a modern guided weapon will be established based on the current and perceived threats at the time the design is commissioned. However the design of a modern guided weapon is a long and expensive process which can result in the weapon entering service only for the original threat to have changed or passed, inevitably inducing a capability gap. The defence budgets of the major military powers such as the UK and USA continue to shrink. As a result the emphasis of military research is being placed on adapting current legacy systems to bridge these capability gaps. One such gap is the requirement to be able to intercept small relocatable, highly manoeuvrable targets. It was demonstrated a number of years ago, that the performance of a legacy weapon against manoeuvering targets could be potentially increased by retrofitting a data link to the weapon. The data link allows commands to be sent to the weapon in flight. The commands will result in the weapon executing one or more manoeuvres which will change the shape of the trajectory. This has the potential to improve the performance of current Advanced Anti-Armour Weapons (AAAW) against manoeuvring targets. The issue which arises from data linking any weapon including an AAAW, is that the ability to shape the trajectory of the weapon will be limited due to the original design parameters of the non data linked system. Therefore in order to obtain the maximum performance increase, the trajectory shaping (retargetting) capability must be efficiently utilised over the duration of the weapon fly out. It was postulated in this thesis that this could be achieved using an integrated fire control system, which would seek to calculate an optimal shaped trajectory. The optimal trajectory should maximise the ability of the weapon to respond to target manoeuvres, thereby improving the probability of a successful intercept occurring. The potential effectiveness of an integrated fire control system was explored by considering the scenario of a generic data linked AAAW which is to intercept a small highly manoeuvrable surface vessel. A total of three integrated fire control systems were developed which calculated the optimal trajectory for different criteria. The first system optimised the weapon trajectory considering multiple predicted target trajectories. Each trajectory had an associated probability. For a given weapon trajectory, the seeker would be able to detect the target at one or more locations along certain predicted target trajectories. The sum of the probabilities associated with the detectable locations represented the total probability of intercept. The weapon trajectory was optimised by calculating the trajectory which achieved the maximum probability of intercept using simulated annealing and simple search optimisation algorithms. The second system optimised the weapon trajectory considering only the most probable trajectory (M.P.T) from a distribution of predicted target trajectories. Appropriate commands were calculated such that a location along this M.P.T trajectory was detectable at some instant in time. The third system presented in this thesis optimised the trajectory considering the maximum probability of intercept initially and then only the M.P.T trajectory later on in the engagement. The three integrated systems and a Fire and Forget system were tested against 80 random target trajectories. In each of the integrated fire control systems, the performance of the AAAW against manoeuvring targets was significantly improved when compared to the Fire and Forget results.

Investigation into the dynamic characteristics and decaying behaviour of SF6 arcs during the current-zero period is of great significance to improving the interruption performance of high voltage circuit breakers and ensuring their reliable operation. The present research was conducted by means of modeling and experiment to provide a better knowledge of the switching process to help the design and optimization of high voltage SF6 circuit breakers. The first part of the work concerns the determination of thermophysical properties of SF6 plasmas under local thermodynamic equilibrium state (LTE). A systematic comparison with transport coefficients obtained using an old data set and experimental test has been performed to check the reliability of the proposed phenomenological approach in evaluating transport cross sections. Properties especially transport coefficients become sensitive to the choice of Debye length definition predominantly due to the different collision integrals affected by the different screening distance. Pressures increase can also influence thermophysical properties due to the inhibited chemical reactions. Moreover, the thermophysical properties under non-equilibrium conditions have been investigated using a two-temperature model. It was noted that the special case with equal electrons and heavy species temperatures produces results agreeing excellently with those obtained by the LTE model. The forms of mass action laws as well as the choice of reaction excitation temperature for molecular ionization used in the calculation can significantly modify the species composition and plasma properties. This model lays the micro-theoretical foundation for a deeper understanding of SF6 plasma formation and evolution mechanism and provides a reliable properties input for non-equilibrium arc behaviour simulation. Following a traditional approach of arc modelling assuming LTE, considerable effort has been devoted to study the arc-shock interaction and its influence on the dynamic characteristics and current zero behaviour of SF6 arcs in a supersonic nozzle with a hollow contact. It was found that the close coupling between the shock region and its surrounding gas flow greatly influences the aerodynamic and electrical behaviour of a nozzle arc and hence the thermal recovery process. In addition, deceleration of gas flow caused by the shocks and enhanced turbulent cooling brought by the sucked gas interacting with the arc both play a significant role in the determination of the thermal interruption capability. Possible departure from LTE in a decaying SF6 arc was studied using a two-temperature hydrodynamic model in a supersonic nozzle under well-controlled conditions. The predicted radial temperature variation presents quite good agreement with test result using emission spectroscopy. It is demonstrated that the electron and heavy-particle temperature diverge in cases where the collision energy exchange is ineffective. For the arc decay phase, the two-temperature model gives a lower cooling rate than the LTE model, and hence a higher conductance of the discharge passage at current zero showing the necessity of using a two-temperature model to accurately predict the current interruption capability of SF6 gas-blast circuit breakers. For thermal recovery phase, considering the chemically non-equilibrium effect, a global kinetic model of decaying SF6 arcs was established to study the electrons elimination mechanisms around current zero. For dielectric recovery phase, the critical dielectric strength of hot SF6 are investigated based on a two-term Boltzmann equation solution of electrons energy distribution function. It is noted that the main mechanisms of electrons elimination are the dissociative attachment from 3500K to 7500K, electron-molecular ion recombination in the temperature lower than 3500K. The temperature increase, pressure decrease and departure from chemically non-equilibrium can all contribute to the dielectric strength reduction. The entrainment of PTFE ablation vapour can enhance the dielectric strengh of SF6 above 2500K. Finally, this research manufactures a model SF6 gas blast interrupter and investigates the dynamic characteristics of electrical, light radiation, pressure along together with electrode movement. Arc dynamic characteristics and decaying behaviour of CO2 and N2 is compared with that of SF6 arcs in order to obtain the dominant properties influencing arc quenching. It is noted that the extinction voltage, which decreases with increase in the interrupting current, is related to the conductance decay during current zero period and can be considered as an evaluation of interruption capability. Gas blast can bring a much more rapid variation of arc resistance and a much higher cut-off current before its extinction. SF6 has a superior interruption capability possibly due to its high thermal conductivity and specific heat.

Knowledge of the ion temperature (Ti) is important for tokamaks when determining plasma parameters from diagnostics which require knowledge of the ion and electron temperature (Te) and also because ions of high energy could damage plasma facing components by sputtering on high power devices. In the tokamak edge there are limited data for Ti, however the few existing measurements show that, beyond the confined plasma, Ti > Te, unlike in the confined plasma where ions and electrons are thermal coupled. A measurement technique using retarding field energy analyser(RFEA) probes to measure Ti has been implemented on the Mega Amp Spherical Tokamak (MAST) to allow measurements at the midplane and also at the divertor target which are two key areas in the scrape-off layer (SOL) plasma. Measurements in ohmic low confinement (L-mode) plasma discharges have shown that Ti ≈ 2Te at the midplane, while Ti ≈ Te at the target. Additionally heated L-mode plasmas have shown that Ti can be greater than Te at the divertor target. In inter-ELM high confinement (H-mode) plasmas, Ti is often found to be higher than Te, with extremes in high power plasmas of Ti/Te ≈ 3 at the target. Initial measurements of the temperature of ions released by an average ELM show that Ti reduces with distance from the strike point at the target. The measured upper limit on Ti in an average ELM reduces from 60 eV to 30 eV over ∼ 4 cm radially at the target. Measurements made by the target RFEA during ELMs show peak Ti ∼ 35 eV compared to peak Te measurements by Langmuir probes of ∼ 25 eV. These initial measurements of Ti agree with modelling of the ELM evolution in the SOL which show hot electrons arriving at the target before the remaining particles released by the ELM. Measurements by RFEA probes are subject to a correction in the presence of parallel flows in the SOL. It has been found from modelling of the MAST SOL that measurements made by the target RFEA should be multiplied by a correction factor between 0.65 and 0.7. Although this reduces the ratios measured of Ti/Te, measurements in inter-ELM H-mode and additionally heated L-mode plasmas would still show Ti > Te at the target. In ohmic L-mode plasmas, however, the reduction in Ti would mean Ti < Te.

Electrical discharges have been used extensively in devices for interruption of fault currents. Much work has investigated the use of arc discharges for interrupting DC current. The problem with DC current is that there is no natural current zero where thermal losses from the arc dominate thus leading to arc extinction and the interruption of fault current. Helical arc been arranged by using splitter blades to separate the arc turns. The expansion of a helical arc confined between polymeric splitter blades is governed by both electromagnetic and aerodynamic forces. These arise due to the complex interaction between the individual arc turns, arc/ splitter blade interactions and surrounding media. These interactions can be exploited to control the rate of expansion. During this expansion stage there is a substantial increase in arc voltage which in low voltage systems can limit the current thereby causing current interruption providing the arc quenching conditions are suitable. An experimental study has been undertaken to assess the fundamental characteristics of helical arcs con�fined between �different arrangements of PTFE, PE and copper blades in three different sizes (180mm, 360mm and 500mm). Significant improvements in arc current limitation and interruption capability are observed when the arc voltage increases. A substantial increase in arc voltage was observed for all combinations of copper/ PTFE splitter blades. It was noted that the prospective fault current is forced to near zero when copper blades are used in conjunction with PTFE blades. With the larger PTFE and PE blades sized 360mm and 500mm, it was observed that the arc stayed within the limit of blades, thus providing better arc control capability. Simplified modelling of the forces acting on the arc (electromagnetic, aerodynamic) have been assessed. The electromagnetic forces act not only to produce radial expansion of the arc but also to keep alignment between the turns. The generation of the aerodynamic forces is very complex to model and indeed the modelling presented can only be used indicatively in any analysis at this stage. The work indicates that a compact DC interruption device may be possible based on the confinement of the plasma within the splitter blades and interaction with polymeric material.

This thesis focuses on four inter-related research topics on the design and analysis of compact planar ultra wide-band (UWB) monopole antennas for future wireless communications, namely, a planar super-wide-band (SWB) monopole antenna, a planar UWB antenna with band-notched characteristics, a planar UWB antenna with reconfigurable band-rejection features, and a planar UWB multiple-input and multiple-output (MIMO) antenna. A novel Mickey-mouse shaped planar monopole antenna with SWB performance is proposed and investigated. Three different techniques for bandwidth enhancement are implemented. The antenna is evolved from the traditional circular monopole antenna and has achieved an impedance bandwidth of more than 100:1 and a stable radiation patterns over a wider bandwidth. The design of a compact planar UWB monopole antenna (22 mm × 34 mm), incorporated with five m-shaped resonators (MSRs) at different positions, to achieve quintuple-band-notched performance is presented. The frequency-domain performance (in term of reflection coefficients, realized gain, efficiency, and radiation pattern), and time-domain performance (in term of pulse responses and fidelity), are investigated by simulation and measurement. The results show that the proposed UWB antenna has approximately omnidirectional radiation patterns and excellent band-notched behaviours and good time domain performance with the fidelity of more than 85.5% in the pulse response. A planar UWB monopole antenna with reconfigurable band-notched characteristics is also introduced. The band rejection is realized by incorporating two co-directional split ring resonators (CSRR) on the radiator element. Switches are added to the CSRR structures to achieve the reconfigurability. The proposed antenna can operate at different switching states including a UWB state, single and dual band-notched states with good rejection behaviours. Good radiation patterns and gain values are also obtained for different switching states. This compact wideband antenna can be very good candidate for a wide range of mobile portable applications. A compact planar UWB-MIMO antenna (60 mm × 45 mm) is presented for wireless applications. The wideband isolation of more than 15 dB is achieved by etching a new trident-like slot on the ground plane of the antenna. An equivalent circuit have been introduced for analysis and the diversity performances are studied. The results show that the proposed MIMO antenna is a very good candidate for wireless applications. The study of these four special antennas has demonstrated that, using various techniques, the planar monopole antenna can be an excellent choice for a wide range of wireless communication applications.

This thesis describes experimental and numerical investigations of various electrokinetic techniques on fluorescent particles, bacteria and protein motors. The aim of this work is to extend the knowledge on the object manipulation, which is an essential part of a practical microfluidic device. The dissertation consists of three major sections that contain novel approaches to object manipulation using electric fields. The effect of dielectrophoretic force on fluorescent particles is analysed first. Using an experimental setup with a controlled switch for the input signal, the theoretical framework for amplitude modulated responce of dielectrophoretic force is developed. Also presented is the image processing software for quantitative particle motion analysis. Another analysis of various electrokinetic techniques (dielectrophoresis, AC electroosmosis, AC electrothermal flow and electrophoresis) was carried out on Pseudomonas Fluorescence bacteria in a solution that supports its growth. These bacteria usually live in geometrically restricted spaces and so spatially confined transparent channels were created to mimic their natural environment. It was noted that in these conditions the motile bacteria do not experience the effect of dielectrophoretic force. The minimum frequency that can be applied to the solution without forming bubbles is too high to distinguish AC electroosmotic effect. Using the numerical simulation, however, the experimental setup that utilises the observed effect of electrophoresis and AC electrothermal flow is designed. The final study was carried out on protein molecular motors. The novel experimental setup to investigate the effect of the electric field on the actin filament motility on five different surfaces, covered with myosin II motors, was developed. The application of higher external electric fields resulted in different velocity increases on different surfaces. Using the numerical simulation, this difference is quantitatively explained by the variation of the number of motors on surfaces. Also presented is a novel method that enables determining the forces exerted by the population of active and resistive motors without the need of expensive equipment.

There is an increasing interest in energy harvesting. The rectenna, which is a combination of a rectifier and an antenna, is a device to harvest wireless energy in the air. This thesis is concentrated on the analysis, design and measurement of compact rectennas for radio frequency (RF) wireless energy harvesting applications, and the thesis can be divided into three parts. The first part is about broadband planar dipole antennas with an unidirectional radiation pattern which is suitable for wireless energy harvesting applications. With the rapid development of various wireless systems, there is a need to have a broadband rectenna for energy collection. The antenna is optimized by changing the dipole shape, diameter, feed gap and the spacing between the antenna and the ground plane. It is shown the optimized antenna has a broad (from 2.8 to at least 12 GHz) with the ability to produce unidirectional radiation pattern. It is a good candidate to form a wideband dual-polarized antenna array for applications such as the wireless power transmission and collection. In addition, a simple rectenna and duel-polarized rectenna arrays are presented. The measurement of the rectenna array is shown that the design has produced the desired DC power with reasonable efficiency. The study is confirmed that the more elements in the array, the higher output voltage although the bandwidth is not as wide as expected because of practical limits. The second part is about a novel wideband cross dipole rectenna for RF wireless energy harvesting. The proposed device consists of a cross dipole antenna, low-pass filter (LPF) and voltage doubling rectifier circuit using Shottcky diodes as rectifying elements. It works over the frequency range from 1.7 to 3 GHz for the reflection coefficient less than -10 dB. Besides, the proposed rectenna can convert the RF energy into DC energy with a good conversion efficiency of up to 75% for high input power density levels (>5 mW/cm^2). In addition, another wideband rectenna built on FR4 substrate is optimized for low input power and the rectenna is optimized, built and measured. A further investigation for the input impedance of rectifier is also conducted. Experimental results demonstrate the rectenna has wideband rectification performance and the maximum rectenna conversion efficiency at 1.7 GHz is more than 50% for the power density of 0.1 mW/cm^2. The third part is about improving rectenna conversion efficiency for low input power density. Increasing the rectenna conversion efficiency for low power density is significant for improving rectenna performance. Currently, there are few of research focused on wideband rectenna arrays for low input power. A new wideband rectenna array with a reflector is developed to increase the rectenna conversion efficiency and output voltage through increasing the gain of the antenna. In addition, two connection methods are used to build the rectenna array and advantages and disadvantages for each method are presented. The RF to DC conversion efficiency of proposed rectenna arrays is much improved for low input power density over a wide bandwidth. This research has produced some important designs and results for wireless energy harvesting, especially in wideband rectennas, and is a solid step towards possible widespread applications of rectennas in the near future.