Dielectric resonator (DR) filters are widely used in microwave communications due to their small size and high Q-factor. Multi-mode filters offer a further level of miniaturisation. A new multi-mode dielectric resonator filter is presented in this thesis. The TE11d dual-mode DR offers an 11% size reduction ratio compared with a coaxial air-filled filter with the same unloaded Q-factor (Qu) and about 820 MHz spurious separation from the fundamental frequency 1.95 GHz. Two coupling techniques are applied in the TE11d filter configuration. These are: ceramic puck/probe in contact and etching holes through the ceramic puck for probe installation. A 4th order Chebyshev filter dual-mode DR filter has been simulated and fabricated using each technique. The results show a good agreement between the simulation and measurement with half spurious-free window compared with non-loaded cavity. In the etching method, the spurious-free window and the Qu improved compared with unpatterned ceramic puck. The inline structure filter provides an extra improvement in the spurious window base for the planar configuration. Another approach to the dual-mode DR filter has been studied in this work. A HE11 dual-mode with ceramic puck placed at the base of the cavity presents a good size reduction ratio and acceptable spurious window. The mathematical model shows that transmission zeros (TZs) can be generated in all orientation cases of the inter-resonator coupling hole. The control range of the TZs positions was from 40 MHz from the centre frequency. A good agreement was obtained between the simulation and the measurement results. A triple-mode DR filter with two-piece of the ceramic puck in parallel has been presented. The one cavity approach offers a high Q-factor with 400 MHz suppression. A coaxial probe was used for the input/output coupling and the etching hole through the ceramic puck for inter-resonator coupling. A 3rd order Chebyshev DR filter was simulated and fabricated with two TZs on the upper sideband. The practical results show prospects in application of the filter for miniaturised microwave communications.

The increasing demand for effective and compact thermal solutions for the next generation of thin and high-power density consumer electronics is challenging the capability of miniature mechanical systems to meet the required cooling performance. Due to their attractive and unique advantages with no moving parts, design flexibility, small-scale structure, low height profile, silent operation, and effective flow generation, electrohydrodynamic (EHD) air movers are well positioned to become a key emerging cooling technology as alternative to conventional rotary fans. In its general objective, this thesis aims to investigate the benefits and highlight the features of EHD air movers as a thermal management cooling solution in advanced and small-scale microelectronics, supporting all previous efforts in this direction. Due to the strong influence of the geometric parameters of EHD devices on the corona discharge process and the resulting EHD flow, numerical modelling represents a powerful tool to design and optimize EHD devices, especially of complex and small-scale structures, where the capability of experimental investigations is limited or challenging. This study presents an accurate and validated numerical method to solve the coupled equations of electrostatics, charge transport and fluid flow for the two-dimensional (2D) modelling of EHD airflow induced through a wire-to-plane/grid channel configuration, and is the first to develop a three-dimensional model (3D) that couples the EHD flows with conjugate heat transfer modelling. Based on thermal management requirements and from a design perspective, a comprehensive investigation and analysis into the influence of geometric parameters on the efficiency of EHD wire-to-grid blowers is performed and optimal configurations are proposed for a range of heights from 9 to 15 mm. Results reveal that using fine emitter wires is more efficient than thicker ones, and the grounded electrode locations affect significantly the electric field distribution and the blower efficiency. It is also found that using the grid as a further collector increases the blower performance, with higher flow production, lower operating voltage and reduced blower size. Further numerical developments are devoted to optimize the configuration of miniature wire-to-plane EHD blowers for heights up to 10 mm, which is the most preferred geometry for integration in the cooling systems of thin electronic applications. For ranges of fixed operating power and voltage, the efficient optimized electrode gaps are predicted and defined by simple expressions. The influence of channel sidewall on the EHD flow rate and velocity profile are investigated and the results show that the 2D modelling is valid to effectively predict flow rates produced by wide and short EHD blowers compared to that obtained by 3D simulations. A combined EHD air blower that enables a reduction in the level of applied voltage and a control of flow production is developed. Performance comparisons against commercial rotary blowers demonstrate that the optimized miniature EHD blowers are more competitive for cooling miniaturized and extended heated surfaces based on blower size, flow rate with uniform velocity profile, and power consumption. A novel design of an EHD system integrated with compact heat sinks is presented as a thermal management cooling solution for advanced and thin consumer applications. Results of a parametric study demonstrate that the EHD system offers flexible structure design with the ability to reduce the height and increase the width as required, providing a unique feature to be installed in low-profile laptops. Moreover, compared to traditional cooling systems used in the current standard low power laptops, the proposed EHD system offers promising cooling performance with higher thermal design power (TDP), reduced thermal solution volume and lower height profile.

The prevalence of lower limb amputation has been rising rapidly with the primary causes associated with dysvascular disease and traumatic injuries. The knowledge of muscle coordination during walking could help in the rehabilitation of individuals with limb loss. The goal of this research was to investigate the neuromuscular differences between healthy subjects (HS) and lower limb amputees during the walking task at different states and speeds using different statistical approaches. High dimensional (HD) electromyography (EMG) data for ten muscles were collected from thirteen healthy subjects’ (HS) dominant leg and eleven transfemoral amputees’ (TFA) intact leg (IL) during transient-state walking at three self-selected speeds (slow, normal, and fast). This data were analyzed at two levels from two different approaches: the HD EMG/muscle activation pattern and low dimensional muscle synergy/modular motor control which were obtained using the linear envelope of EMG signals and concatenated non-negative matrix factorization (CNMF), respectively, from biomechanics and robotic control approach. While the biomechanics approach considers the covariance between the HD muscle activities and low dimensional temporal components of muscle synergy, robotic control accounts for individual muscle activities and temporal components of muscle synergy using statistical parametric mapping (SPM). HD EMG data for ten muscles were also collected from four HS and one transtibial amputee’s (TTA) IL and prosthetic leg (PL) during steady-state walking at a self-selected speed. The muscle synergy was analyzed using the developed CNMF algorithm among legs in pairwise comparisons. The effect of speeds on both HS and TFA muscle activities from biomechanics and robotic control perspectives showed statistically significant differences, suggesting neuromuscular adaptation mechanism in both groups to satisfy the kinematic and kinetic demands of increasing transient-state walking speed. Some differences in HD muscle activities related to the plantarflexors could be observed among the groups, indicating compensatory adjustment of TFA IL for the lack of push off from the PL. The effect of speeds on HS muscle synergy vectors showed reasonable correlations as opposed to those of TFA synergy vectors during transient-state walking. The high correlation suggests that the central nervous system (CNS) activates the same group of muscles synergistically. In comparison among HS dominant leg, TTA IL and TTA PL, the primary muscle(s) had a significant impact on the level of muscle synergy vectors correlation. The activation coefficient profiles suggested that amputees’ IL and PL were significantly different when compared together and to the HS. The same number of synergy groups (=4) found in HS, TFA and TTA indicate analogous complexity implemented by the CNS which does not depend on the state of the gait cycle (transient vs. steady), speed (slow, normal and fast), and level of amputation (below knee vs. above knee). These results have important clinical and robotic control implications. It could provide useful information to therapists to tailor rehabilitation strategy to focus on the muscles and the timing where significant differences occur in the gait cycle. As a result, this could decrease the risk of secondary physical conditions (e.g., osteoarthritis) and increase gait efficiency. The information may also be useful for the prosthetic manufacturers to design prostheses that incorporate information from the IL and/or PL to improve the myoelectric prostheses and develop synergy-based control frame.

This thesis is concerned with solar energy storage systems in terms of storage materials and storage systems for high temperature applications. The main focus has been given to either improve the thermophysical properties of the storage medium or to improve the design of the storage medium by optimizing the solar energy storage system. Nitrate salts have been chosen as the phase change material with nanoparticles as additive materials. Different types or concentrations of nanoparticles and different types of nitrate salt have been selected and studied. There are different objectives, starting from a few grams (up to 5 g) to kilograms (up to 3 kg), that have been considered through this research. In the first objective, nanosalts, which are nanoparticles seeded in the nitrate salts, have been prepared by two different methods, either the 2-step method or the 1-step method. Nanosalt prepared by the 2-step method showed higher specific heat capacity (cp) than the base salt by 10.5% with higher thermal conductivity (k) values up to 60%. Up to 6% increments in total thermal energy storage have been observed for nanosalt (iron oxide (Fe2O3) nanoparticles and binary nitrate salt). Additionally, the 1-step method was used to prepare copper oxide (CuO) nanoparticles directly inside the nitrate salt, which showed improvements in cp in comparison to base nitrate salt. In the second objective, alongside with the thermophysical properties measurements, material characterizations have been considered using different devices to show the morphology of the surface area of salts and nanosalts samples. In the third objective, an experimental rig has been designed and built to study heat transfer of salts and nanosalts. Temperature measurements have been made at different axial, radial and azimuthal locations. Both charging and cooling of the salt (or nanosalt) were studied, showing that improvements in the charging process are related to the type or concentration of the nanoparticles material. Overall, heat transfer is improved in the case of nanosalt compared to salt alone. Two different types of salt were tested in this experiment rig which was single salt (sodium nitrate) and binary solar salt (sodium nitrate: potassium nitrate by 60:40 molar ratio) with different additives materials such as CuO (by 0.5 wt. %) and Fe2O3 (by 0.1 wt. %, 0.5 wt. % and 1 wt. %). In the fourth objective, Computational Fluid Dynamics software has been used to solve the charging process of salt and nanosalt. A validation for the ANSYS CFX code (version 17.0) is conducted by comparing the experimental data with the simulation data. A good agreement is obtained for both cases of salt or nanosalt. In the fifth objective, an optimization for the solar energy storage system has been conducted. Different designs for the storage system employing finned structures were studied. The new combination effect of both nanosalt and fins system has been studied using the validated CFX code, showing a promising improvement in the charging process in comparison to salt alone, nanosalt alone or salt-fins system alone. As a result, our overall aim is to improve the thermal properties of nitrate salts and optimize the thermal energy storage system.

Among all emerging quantum information technologies, quantum key distribution (QKD) is one of the most developed techniques. QKD harnesses the intrinsic laws of quantum mechanics to provide a method for distributing secret random keys, which can be used for data encryption and decryption between two intended users. QKD has already been demonstrated in different scenarios over optical fibre and in atmospheric channels. QKD has also been used for security assurance in several network settings, in addition of being commercially available today. Despite remarkable progress in QKD systems, convenient access to the developing quantum communications networks is still missing. Adopting QKD in mobile devices would enable such a service, particularly, in indoor environments. This is in line with the recent advancement in fabricating microchip-scale QKD devices, which would ease this incorporation into mobile devices. This work focuses on the access networks, and, in particular, it addresses the wireless mode of access in indoor environments for QKD networks. We find a practical regime of operation, where, in the presence of external light sources and loss, secret keys can be exchanged. We then propose practical configurations that would enable wireless access to hybrid quantum-classical networks. The proposed setups would allow an indoor wireless user, equipped with a QKD-enabled mobile device, to communicate securely with a remote party on the other end of the access network. We account for adverse effects of the background noise induced by Raman scattered light on the QKD receivers due to the transmission of both quantum and classical signals over the same fibre. In addition, we consider the loss and the background noise that arise from indoor environments. We consider a number of discrete and continuous-variable QKD protocols and study their performance in different scenarios. In our analysis we consider the asymptotic scenario, as well as the finite-size key effects. In the former case, an infinite number of signals are assumed to be exchanged between the sender and the recipient, whereas in the latter, which represents the practical scenario, a finite number of signals are exchanged between the two users. Our results indicate that a feasible regime of operation for wireless QKD exists. This makes the QKD technologies available to end users of a communications network.

This work presents the development and characterisation of single and multilayer Diamond-Like Carbon (DLC)-graphene nanoplatelet (GNP) nanocomposite coatings. This study opens up a new challenge in the fabrication of carbon composites using DLC and GNP with enhanced mechanical and tribological properties. The purpose of the composite is to exploit the advantages of the excellent mechanical and tribological properties of graphene that have been reported by many works. The objectives of this thesis are to develop a method to fabricate DLC and GNP nanocomposite coatings, to prepare the nanocomposite coatings and to investigate their physical, mechanical and tribological properties. The fabrication of DLC-GNP nanocomposite coatings was carried out using the combination of spin coating of GNP and DLC deposition using PECVD. The two types of DLC-GNP that have been prepared are single-layer and multilayer. The surface morphology and microstructure of DLC-GNP was characterised using optical microscopy and Scanning Electron Microscopy (SEM). Focused Ion Beam (FIB) SEM was used to observe the layers in the composite and measure the thickness of the multilayer DLC-GNP nanocomposite coating. The coating comprises the interlayer, spin-coated GNP and DLC film. This study shows that an optimised post-treatment is required to substantially improve the adhesion strength of spin-coated GNP and thus that of the whole nanocomposite coating. It was observed that columnar structure was generated in-situ during a wear tests on coatings post-treated for more than 180 minutes. The results were unintentionally found after three hours of sliding test. The columnar structure contributed to the significant reduction of the coefficient of friction (CoF) to 0.06, and the wear rate compared to other samples. According to Raman spectroscopy analysis, both single and multilayer DLC- GNP nanocomposite coatings have typical spectra similar to that of pure DLC. However, DLC-GNP has a broad range of ID/IG ratio values compared to pure DLC due to the dispersion of spin-coated GNP. The observation though cross-section FIB also proved that DLC film covered the spin-coated GNP by creating a bonding layer during DLC film deposition. The multilayer DLC-GNP demonstrated major improvements in adhesion strength of almost doubling the value obtained by single-layer DLC-GNP. The wear resistance also increased remarkably which can be related to the enhancement of adhesion strength. It is proposed that the GNP in the composite is released during the running-in period and acted as a slider between the counterpart and coating.

Model-in-the-Loop (MiL) testing is a method in which the test object is split into a physical part and a simulated part, and these are connected with interfaces to form a combined physical-numerical system. It is introduced to combine the advantages of physical test and computer simulation: the part of the system which is difficult to implement physically can be put into the numerical subsystem to reduce the cost and complexity of the physical test, and the key components with unknown characteristics or with some characteristics which are difficult to model can form the physical subsystem. The simulated part also provides the flexibility to change the parameters during the test. In this thesis, the structure and the characteristics of MiL systems are analysed. Detailed results are given using two example systems: a single mass-spring-damper MiL system, and a two Degree of Freedom (DOF) mass-spring-damper MiL system. The systems are defined, and a procedure for stability analysis is given. The influence of the actuator dynamics and the measurement noise introduced by the sensors is discussed. To compensate for the actuator dynamics, compensators are introduced to the MiL system. It is shown with simulation results that, when a compensator based on an inverse of the actuator dynamics is added to the MiL system, the high frequency measurement noise may be greatly amplified in the compensated signal, and therefore signal saturation may occur which leads to unacceptable testing results. To design a compensator which can effectively compensate for the actuator dynamics, while reducing the tendency of signal saturation in the compensated actuator control signal at the same time, H∞ optimization is applied. A general model is composed for the H∞ optimization, where the target testing result is compared with that of an ideal reference model, and the error between them is minimized via H∞ loop shaping. The principle of H∞ loop shaping is presented in the thesis, and its use as a general MiL optimization procedure is proposed. The optimization method is verified with the example one and two DOF mass-spring-damper MiL systems. The simulation results show that, for both of the examples, the H∞ optimized compensator can compensate for the actuator dynamics accurately, and attenuate the response excited by the measurement noise in the compensated signal effectively. The balance between accuracy and high frequency noise attenuation can be adjusted by the weighting functions. The effectiveness of the H∞ optimized compensator is then verified with experimental results. A two-axis robotic arm based on a limb of the Italian Institute of Technology HyQ robot was used for the experiment. The H∞ optimized compensator is compared with various alternative compensators, and the H∞ optimized compensator show its advantages in terms of an appropriate balance between accuracy and saturation rejection. Lastly, a performance envelope analysis is introduced to give a guide to choosing suitable hydraulic actuators and valves for a specific MiL test based on the actuator performance required to give desired test accuracy. Although the H∞ optimized compensator can broaden the usable frequency range of the valve/actuator system, and will provide a larger margin for control signal saturation, an effective test system is only achievable if an actuation system of adequate performance is chosen.

Aircraft encounter increased aerodynamic loads when exposed to gusts, turbulence andmanoeuvres. Currently, these loads are mitigated through the use of ailerons and spoilers to reduce lift, in turn reducing the loads passed to the aircraft structure. However, these actuators are limited in their frequency response and cannot control loads produced by higher frequency events. Therefore, an actuator which can mitigate high frequency oscillatory loads is required, with a deployment reduced frequency, k of up to 1. One such promising load control actuator is the minitab, consisting of a small span-wise strips, similar to the Gurney flap, deployed normal to the airfoil upper surface. Key to the actuator’s high frequency response is its low inertia, meaning that a small energy input can achieve a significant effect. To investigate the efficacy of the minitab on load alleviation a series of steady state, periodic and transient measurements were conducted at a Reynolds number of 6.6 x 105. These experiments aimed to fully evaluate the effect of chordwise location, mini-tab height and angle of attack on steady state load control. The dynamic response was categorised, in terms of magnitude, phase and time delay by the periodic and transient measurements. Mini-tabs of height h/c = 0.02 and 0.04 were employed in a steady state configurationacross a range of chordwise locations to investigate the effects of mini-tab height and chordwise position. Overall, the mini-tab was found to have a lift reducing effect which increased with height. It was found that the effect of the chordwise location was highly dependent on the angle of attack. Placement close to the trailing edge induced a large effect at α = 0°, creating an effective change in camber comparable to conventional Gurney flap use. Peak suction over the lower surface increased resulting in a reduction of ΔCL = -0.48. Approaching stall, effectiveness decreased as the mini-tab became immersed in the separated flow. Placement at xf/c = 0.60 produced an almost constant lift reduction between α = 0° and 5° of ΔCL ≈ -0.60, with a gradual reduction to stall. A mini-tab positioned close to the leading edge (xf/c = 0.08) was found to separate the flow effectively at low incidences but with no noticeable change in lift observed. It was found that the flow separation produced by the mini-tab effectively eliminated the suction peak on the upper surface. However, placement close to the leading edge has increasing effectiveness towards stall, as the shear layer induced by the separation was displaced further from airfoil surface. Peak lift reduction at stall was found to be ΔCL ≈ -0.67. The optimum chordwise location for peak lift reduction is dependent on the airfoil angle of attack: the position of the mini-tab for maximum lift reduction moves towards the leading edge as the angle of attack increases. The second stage utilised a deployable mini-tab up to reduced frequencies, k = 0.79, placedat xf/c = 0.85, to assess the mini-tab’s frequency response. The force measurements indicate that the mini-tab has a decreasing effect on lift reduction with increasing actuation frequency. This trend is comparable to Theodorsen’s function, based on the change in circulation. For α = 0°, the normalised peak-to-peak lift reduction decreased from 1 for steady state deployment to around 0.6 at k = 0.79. In addition, a phase lag exists between the mini-tab deployment and the aerodynamic response which increased with actuation reduced frequency, k. However, the measured phase lag is substantially larger than Theodorsen’s prediction. Increasing the angle of attack, α reduced the mini-tab’s effect on lift while increasing the phase angle when comparing equal k values. Particle Image Velocimetry measurements indicate that the delay and reduction in effectiveness of periodic deployment is due to the presence and growth of the separated region behind the mini-tab. Overall, the mini-tab was found to be an effective, dynamic lift reduction device with the separated region behind the mini-tab key to the amplitude and phase delay of lift response. Finally, the aerodynamic response of the mini-tab was investigated during a transientdeployment. The delay in aerodynamic response to mini-tab actuation was consistent with literature. The normalised deployment period, τdeploy did not provide a significant alteration in the aerodynamic response for deployment periods below τdeploy = 3, with the aerodynamic response reaching the steady state value around τ = 6-8. The aerodynamic response of the mini-tab was approximated using a simple, 1st order system response to a ramp-step input of gradient 1/τdeploy, indicating that the aerodynamic response of the mini-tab is further delayed for higher angles of attack, due to the presence of separated flow in the vicinity of the mini-tab. PIV measurements were utilised to analyse the effect of transient mini-tab deployment, indicating a delay in the development of the separation region created by the mini-tab, producing a corresponding delay in aerodynamic response. In addition, outward deployment was found to have a slower aerodynamic response than inward deployment, as the flow was found to take to detach slower than to reattach.

Millions of people are suffering from lower limb loss all around the world. Passive ankle prostheses in the market cannot fully restore ankle function and will cause asymmetrical walking gaits. Several powered ankle prostheses, which provide net power in the stance phase to assist walking, have been developed by the researchers, but their walking range is significantly limited by the power requirement. In this thesis, an electrohydrostatic actuator (EHA) powered ankle prosthesis is proposed. This is intended to actively assist walking at certain points in the gait cycle, namely the plantarflexion (PF) before toe-off and dorsiflexion (DF) in the early swing phase for toe-lifting. In the rest of the gait, the ankle prosthesis actuation system can operate passively with controllable damping. This approach can increase the working time range compared to a continually powered ankle and ensure safe passive prosthetic function after the battery discharged. A prototype of the EHA powered ankle prosthesis has been developed. A 100 W brushless DC motor is used driving a 0.45 cc/rev bi-directional gear pump. The damping ratios of the ankle PF and DF are controlled by bypass restriction valves. The EHA system and the foot springs at the ankle joint weigh 2.2 kg. The controller and a 2 Ah battery are held in a backpack. Walking characteristics with a passive ankle were studied in an amputee trial to gather ankle sensor signals for the controller design. A timing control method is proposed which uses the foot spring strain gauge signals to detect heel strike. A middle stance time delay is added between the end of the heel strike and the start of the powered PF phase. This delay time length can be adjusted to fit different walking speeds. Heel strike detection using hydraulic pressure signals is also studied. The EHA powered ankle prosthesis and its controller has been tested by a 70 kg transtibial amputee. According to the amputee trial results, the EHA can provide sufficient power to assist walking in the terminal stance and the energy consumption in the passive phases are proximately zero. The on-board battery is able to power over 5500 level walking steps. In the amputee trial, the ankle prosthesis controller correctly recognises the heel strike and triggers the powered PF phase. According to feedback from the amputee, the EHA powered ankle prosthesis provided beneficial level walking assistance and a very natural walking gait. The characteristics of the powered ankle prosthesis are analysed by comparing with the healthy ankle and by testing at different walking speeds. A simulation model was developed to help analyse the performance characteristics of the EHA. This includes a brushless DC motor model and a symmetric hydraulic actuation model. The laboratory-based experiment results and amputee trial results are used to analyse and validate the simulation model. The model can be used for future development and refinement of EHA powered ankle prostheses.

In this study composite ferroelectric materials have been investigated for their ability to harvest energy from mechanical vibrations via the piezoelectric effect, and store electrical energy as capacitor materials. A combination of modelling and experimental techniques have been used to understand the consequences of using multiphase materials for energy harvesting and storage applications, with particular focus on the significance of interactions between composite structure, electric field distributions and the effective material properties. A detailed investigation into the properties of ferroelectric ceramic-air composites, such as porous barium titanate, is presented. Introducing isotropic, randomly distributed porosity into barium titanate was found to increase the energy harvesting figure of merit from ~1.40 pm^2/N for the dense material to ~2.85 pm^2/N at 60 vol.% porosity. Finite element modelling was used to better understand the poling behaviour of barium titanate with different porous structures (uniform, porous sandwich layer and aligned), enabling the design of materials with improved energy harvesting capabilities. Complex porous structures were found to have enhanced energy harvesting figures of merit, with maximum values achieved of 3.74 pm^2/N and 3.79 pm^2/Nin barium titanate with a 60 vol.% porosity sandwich layer (overall porosity ~34 vol.%) and highly aligned freeze cast barium titanate with 45 vol.% porosity, respectively. Dense and porous barium titanate samples were mechanically excited and the derived electrical energy used to charge a capacitor. The porous barium titanate was found to charge the reference capacitor more effectively than the dense material, demonstrating the benefits of introducing porosity into ferroelectric materials for energy harvesting applications. Ferroelectric composites, in which either a conductive filler was added to a high permittivity ferroelectric matrix or a high permittivity ferroelectric phase was added to a low permittivity polymer matrix, were evaluated for their potential as a new generation of capacitor materials using finite element modelling. The studies suggested that the rise in effective permittivity due to the forming of composites is fundamentally linked to the rapid decline in dielectric breakdown strengths observed in composites, resulting in nearly all cases reported in the literature demonstrating a reduction in the energy storage figure of merit. It is concluded that future efforts into finding the next generation of energy storage materials should focus on single phase, or intrinsic, high permittivity materials rather than composite materials.