Organic photovoltaics (OPVs) is an area that has attracted much attention recently as a potential low cost, sustainable source of energy with a good potential for full-scale commercialisation. Understanding the factors that determine the efficiency of such cells is therefore a high priority, as well as developing ways to boost efficiency to commercially-useful levels. In addition to an intensive search for new materials, significant effort has been spent on ways to squeeze more performance out of existing materials, such as multijunction cells. This thesis investigates double junction tandem cells in the context of small molecule organic materials. Two different organic electron donor materials, boron subphthalocyanine chloride (SubPc) and aluminium phthalocyanine chloride (ClAlPc) were used as donors in heterojunctions with C60 to create tandem cells for this thesis. These materials have been previously used for solar cells and the absorption spectra of the donor materials complement each other, making them good candidates for tandem cell architectures. The design of the recombination layer between the cells is considered first, with silver nanoparticles demonstrated to work well as recombination centres for charges from the front and back sub-cells, necessary to avoid a charge build-up at the interface. The growth conditions for the nanoparticles are optimised, with the tandem cells outperforming the single heterojunction architecture. Optical modelling is considered as a method to improve the understanding of thin film solar cells, where interference effects from the reflective aluminium electrode are important in determining the magnitude of absorption a cell can achieve. The use of such modelling is first demonstrated in hybrid solar cells based on a SubPc donor with a titanium oxide (TiOx) acceptor; this system is ideal for observing the effects of interference as only the SubPc layer has significant absorption. The modelling is then applied to tandem cells where it is used to predict the short-circuit current (Jsc) generation of the sub-cells, which is not accessible experimentally. Current-matching is then used to predict the Jsc of the complete tandem device. As a support to the optical modelling, ellipsometry measurements of thin films of ClAlPc are presented. These films of known thickness are analysed to extract the complex refractive index for use in optical modelling calculations. A dependence of the complex refractive index on film thickness and substrate is also noted. Finally, the external quantum efficiency (EQE) technique is considered as applied to solar cells, and an additional method is proposed to characterise current balancing in asymmetric tandem cells under illumination. This technique is verified experimentally by two separate sets of data.

There is an increasing requirement to fabricate ever smaller components and microdevices and incorporate them within all aspects of our lives. From a Wii controller to a car airbag, micro-technology is employed in a huge spectrum of applications. Within process control and sample analysis, micro-components are making a significant impact, driven by the desire to use smaller volumes, lower concentrations, less reagent, or simply to make the process quicker or cheaper. Currently, methods of fabrication for such devices are based predominantly on silicon processing techniques. While these techniques are suitable for mass manufacture / high volume applications, there are a number of disadvantages for situations requiring lower volumes or where the end system is continually evolving – such as for research applications. The primary drawbacks are cost, turnaround time and the requirement for expensive processing facilities. However, for these situations, additive layer manufacture presents huge promise as an alternative fabrication technology. The field of additive layer manufacture has advanced greatly since its inception 25 years ago. While such technologies are still primarily focused on the field of rapid prototyping of purely mechanical structures, it is clear that their full potential is yet to be realised. This is particularly the case for stereolithography and microstereolithography, the latter of which provides the capability to create complex, true 3D structures (as opposed to pseudo 3D/extruded 2D of silicon techniques), measureable on the micron scale. This thesis shows that microstereolithography has the potential to become an alternative fabrication method for functional micro-devices and structures. This is due to the simplicity of its single-step fabrication process and the significant time/cost savings it presents. Therefore, making it an affordable technique for low volume production where a fast turnaround is required. However, the lack of functional materials compatible with microstereolithography, and hence the lack of examples of the technology being used to produce active components, currently limits it in this respect. This project therefore focused on exploring the possibilities of using microstereolithography as an alternative to traditional silicon based techniques for the direct fabrication of functional micro-devices and sensors. This was achieved through the development of a number of microstereolithography compatible, novel materials, methods and applications. Here, presented for the first time are both conductive and magnetic composite photopolymers compatible with microstereolithography technology. The materials were developed with the use of a custom built, constrained surface system using a parallel projection method. The system used LED technology as a novel exposure source, tuned to the developed materials in an attempt to gain extra control over the curing process and hence achieve higher quality components. These materials were characterised and then used to fabricate exemplar sensing devices using microstereolithography – a method not previously used for creating such devices. Microfluidic flow sensing devices were used to demonstrate the practical application of the magnetic material. One of which, a lab-on-chip type device, was demonstrated to have a working range of 5 to 70 ml/min when tested with a liquid medium. Similarly, a practical application of the conductive material was shown through the fabrication of MSL-printed conductometirc vapour sensors. The sensors showed favourable characteristics working in range of humidites (up to 50% RH) and temperatures (up to 70°C). The sensors also demonstrated a degree of selectivity to different analyte vapours. Finally, the technology was demonstrated as a feasible method of fabricating ultrasonic beam forming apparatus. Acoustic testing of a range of materials also suggested that the composite metal materials could be used to further improve performance. The novel materials and techniques investigated, along with the exemplar devices produced, demonstrate further abilities and a wider range of applications than has been demonstrated with this technology to date. It is hoped that this research will lead to wider use of the technology and encourage further advances in the field of microstereolithography.

Renewable energy is developing rapidly and gaining more and more commercial viability. High reliability of the generation system is essential to maximize the output power. The power inverter is an important unit in this system and is believed to be one of the most unreliable parts. In the case of wind power generation, especially in off-shore wind, when the system reliability requirement is high, a technique to predict the inverter lifetime is invaluable as it would help the inverter designer optimize his design for minimal maintenance. Previous researchers studying inverter lifetime prediction, focus either at device level such as device fatigue damage models, or at system level which require experimental data for their selected device. This work presents a new method to estimate the inverter lifetime from a given mission profile within a reasonable simulation time. Such model can be used as a converter design tool or an on-line lifetime estimation tool after being configured to a real converter system. The key contribution of this work is to link the physics of the power devices to a large scale system simulation within a reasonable framework of time. With this technique, the system down time can be reduced and therefore more power can be generated. Also, the failure damage to the system is avoided which reduces the maintenance cost. A power cycling test is designed to gather the lifetime data of a selected IGBT module. Die-attach solder fatigue is found out to be the dominant failure mode of this IGBT module. The accuracy of widely accepted Miner’s rule, which accumulates damage linearly, is discussed and a nonlinear accumulation method is promoted to predict the lifetime of power inverters.

An optical wireless transmission technique represents an attractive choice for many indoor and outdoors applications within fixed and mobile networks. It has the advantage of providing a wide bandwidth that is unregulated worldwide, with availability to use it in a very dense fashion, and potentially very low cost. Due to the high attenuation suffered by Infrared radiation through the air, operating low power transmission sources, and generally adverse signal to the noise environment found by ambient background light, where the optical signal is typically at it is minimum power level when detected. A high sensitivity and high selectivity receiver will be imperative for such applications as subcarrier multiplex systems, millimetre-wave radio over fibre and other wireless optical system applications. The thesis details the research, design, and optimisation of a novel, low-noise frontend optical receiver concept using a photoparametric amplifier (PPA) technique, in which the detected optical baseband signal is electrically amplified and up-converted to upperside frequency, based on the nonlinear characteristic of the pin photodiode junction; the desired signal passes through a further signal processing stage, and the original baseband signal is recovered again, using the concept of the superheterodyne principle. The designed DCHPPA receiver acts in a parallel manner to a conventional double superheterodyne detector system, but without the noise penalty normally incurred in the first stage. The PPA is used instead of a resistive/transistor based mixer at the first stage. DCHPPAs have the properties to provide very high gain, with high selectivity, combined with a very low noise operation. The research is conducted from three aspects: theoretical analysis, modelling and simulation, and practical implementation and result analysis. The three approaches followed the same trend shown, and the results correspond closely with each other. Theoretically, a new non-degenerate PPA mode of operation is discussed, in which the applied dc bias to the pin photodetector is replaced by the applied ac pump signal. This is shown to be advantageous in terms of the desirable characteristics for PPA operation, leading to improved conversion efficiency and the potential for low noise operation. PPA was shown to behave more optimally with load resistance which was much lower than normally used in the common optical wireless receiver-amplifiers. A new PPA gain theory was derived and optimised accordance with the original gain theory, PPA input/output admittance power was analysed for optimum power transfer. More accurate DCHPPA circuit configurations were modelled and simulated using nonlinear simulator tools (AWR) which help to understand and optimise system performance, particularly device parameters and characteristics. The full DCHPPA system was implemented practically, and tested in VHF and UHF as a sequel to the simulation configuration, which subsequently exhibited a 34.9dB baseband signal over the modulated optical signal; by employing a chain gain DCHPPA cascaded configuration, 56.3 dB baseband signal gain was achieved. The PPA noise was also measured and analysed, which satisfied the tough front-end optical system requirements.

The intention of the work presented is to provide novel, accurate and time-efficient way of designing multi-sines stimulus signal to replace real-life modulated signals prevailing within telecommunication networks, hence providing a novel tool for the development of modern RF measurement and design solution. The work demonstrated that with 50 tones, the multi-sines stimulus excites almost the same level of nonlinearity as real modulated signals do. For this conclusion the investigation of nonlinear behaviour mechanism was taken and a real DUT was measured under designed multi-siness and various types of modulated signals. It is also demonstrated that this multi-sines stimulus is compatible with the advanced RF measurement systems which are capable of measuring the complete RF waveform including the harmonic and base-band frequencies but demanding a periodical stimulus signal. Furthermore, a novel and quick sub-sampling algorithm was proposed to efficiently use the memory of Sampling Oscilloscope and therefore allows for accurate multi-sines capturing. An averaging algorithm for multi-sines stimulus was proposed to “stabilize” the captured waveform and a PCA based phase compensating algorithm was also proposed to tackle the problem of frequency shift under multi-sines excitation.

Wireless communication systems require an efficient and broadband RF frontend. RF Power Amplifiers (PA) are the most critical component in the RF frontend and are considered the bottleneck in high efficient wideband transmitters. The research starts with an investigation of high efficient operation modes based on waveform engineering. The outcome of the research can be divided into two main parts: The first concerns an analysis of high efficient modes of operation. The second part builds on first part looking at the PA’s efficiency-bandwidth perspective to design a wide band high efficient PA. The first part of the thesis, introduces a novel linear high efficient PA mode termed Injection Power Amplifier (IPA) that exceeds drain efficiency of 90% without relying on the nonlinearity of a PA at the compression region. This is achieved by presenting appropriate negative harmonic impedances to a transistor to reduce the dissipated power, thus, increasing the efficiency of conversion of DC to fundamental RF power. The theoretical analysis of this mode is presented and a validation measurement has been carried out using an active load-pull system. The measured results confirmed the theoretical predictions of achieving high efficiency in a linear PA operation. Furthermore, a PA structure that is based on two parallel PAs (main PA and auxiliary PA) has been proposed along with the practical circuit realization of the IPA mode. In addition, a PA prototype has been designed following a methodology of nonlinear PA design based on waveform engineering. The PA prototype has been characterized and built operating at 0.9 GHz with an output power of 10 W showing a high linear efficient operation of 80% drain efficiency at only 1 dB compression level. The second part of this work aims to tackle today’s limitation of high efficient wideband PAs beyond octave bandwidth. A conceptual system based on multimode operation has been proposed to overcome the need for bandlimiting passive harmonic termination. This novel approach is based on combining passive termination with active harmonic injection to get around the theoretical limitation of one octave for high efficiency harmonically tuned power amplifiers. Furthermore, a proof of concept PA prototype has been designed and built for a two octave bandwidth (4:1 bandwidth) operating from 0.63-2.56 GHz and providing the rated output power of a 10 W GaN device with a PAE greater than 50% at only 1 dB compression point. This multi-mode approach shows a promising technique for future wideband high efficiency wireless transmitters.

The research work presented in this thesis aims to achieve high-power, high-efficiency amplification across substantial bandwidths at microwave frequencies. The push-pull topology was identified as a promising possible solution which had previously not been considered for this application. The key component in the push-pull power amplifier is the balun, which converts between balanced and unbalanced signal environments. The novel use of ferrite materials allowed the half-wavelength resonance of a coaxial-cable transmission line balun to be suppressed, greatly extending its bandwidth. This was done by utilising the resistive properties of the ferrite material at frequencies greater than 1 GHz, at which these materials are not usually studied. The multi-decade performance of the transmission line baluns opened up the possibil- ity of realising push-pull power amplifiers across similar bandwidths. The measurement of these baluns revealed that they present a resistive impedance to the odd-harmonic frequencies, and an open circuit to the even-harmonic frequencies. This is a significant departure from the conventional view of the push-pull mode, and led to the modes of operation inside a microwave push-pull power amplifier being reconsidered. Factorised waveform expressions were used to describe the new modes of operation, and these were verified through load-pull simulations and measurements. The wave- forms were found to resemble the inverted modes of operation, with similar desirable characteristics such as high efficiency and an increase in output power compared to Class A. The viability of the push-pull amplifier topology was demonstrated through two pro- totype amplifiers, which achieved high output power levels and efficiencies over multi- octave bandwidths. Measurement systems for characterising and analysing these amplifiers were developed, which should lead to improved understanding and better performance in future.

As the range of transmission voltage increases, the pollution severity of the site becomes the most important factor in determining the insulation level of the system. Flashover on polluted insulators poses a serious threat to the reliability of the system and leads to system outages. There are many remedial measures to minimize the flashover of a porcelain insulator under pollution conditions. One such method is the application of hydrophobic coatings such as Room Temperature Vulcanizing Silicone Rubber (RTV- SiR) and Grease coatings on the surface of ceramic insulators. A recently proposed solution for contaminated outdoor insulators consists of the application of the Nanocoating “Voltshield” onto the surface of the insulator. This thesis reports a comparative assessment of the performance of these coating systems. Laboratory testing of coated porcelain insulators has been undertaken based on the solid layer method of IEC 60507 (artificial pollution- clean fog testing) and IEC 60587 (the inclined plane tests and constant voltage-liquid contaminants) to evaluate the coatings’ resistance against tracking and erosion. The performance of these coatings was assessed by monitoring the leakage current on the insulator surfaces. The applied voltage and the leakage current signals were acquired throughout the tests and saved for further analysis. The effect of UV radiation on the coatings has also been investigated. In addition, hydrophobicity tests were performed on the coated insulators. It was found that the Nanocoating reduces the leakage current by 90% whilst the energy absorbed on the insulator surface is reduced by 98% when compared to an uncoated insulator. The Nanocoating showed good resilience to sand blasting, but under long exposure to sand blasting, the surface began to degrade and showed pockmarks. The Nanocoated insulator showed good stability under UV exposure in terms of leakage current suppression. However, Nanocoated insulator lost its hydrophobicity on exposure to fog, and has lower flashover voltage than the uncoated insulator by 12.5%. Similar observations were made for the RTV coatings, where the current magnitude reduced by 92%, the energy absorbed on the insulator surface is reduced by 99% when compared to uncoated insulator and the flashover voltage is increased by 50%. RTV coating materials showed good resistance against tracking and erosion even after UV exposure. The electric field and voltage distribution along the leakage surface of coated and uncoated ceramic insulators under clean and polluted conditions were studied using finite element analysis COMSOL Multiphysics®. The electric field peaked at both the HV electrode and the ground electrode, and the presence of pollution in the form of water droplets on the coated insulator increased the electric field at the HV electrode. This study shows that the application of protective coatings to HV outdoor insulators significantly improves their performance. A reduction in surface current and power dissipation is observed, and a reduction in surface heating results in less dry-band arcing. A reduction in dissipated energy can make a contribution to reducing the total loss on the power system. In addition it showed the ability of coatings to resist tracking and erosion which leads to longer coating life under severe weather conditions. The coatings also increased the flashover voltage of the insulators which leads to more stable power system.

In this project an investigation of a wireless power transmission method utilising ultrasonic Lamb waves travelling along plates was performed. To the author’s knowledge, this is the first time such a system was investigated. The primary application for this method is the supply of power to wireless structural health monitoring (SHM) sensor nodes located in remote areas of the aircraft structure. A vibration generator is placed in a location where electricity supply is readily available. Ultrasonic waves generated by this device travel through the aircraft structure to a receiver in a remote wireless sensor node. The receiver converts the mechanical vibration of the ultrasonic waves back to electricity, which is used to power the sensor node. An experimental setup comprising a 1000 × 821 × 1.5 mm aluminium plate was designed to model an aircraft skin panel. Pairs of piezoelectric transducers were positioned along the longer edges of the plate. The electric impedance characteristics of three transducer types were measured. A circuit simulation MATLAB code was written. An input and output power measurement system was developed. The MFC M8528-P1 transducer type was identified as providing the best performance. The use of inductors to compensate for the capacitive characteristics of transducers was shown to provide up to 170-fold power throughput increase. The propagation of Lamb waves in the experimental plate was mapped using a scanning laser vibrometer and simulated using LISA finite difference method software. An optimised laboratory system transmitted 17 mW of power across a distance of 54 cm while being driven by a 20 V, 224 kHz signal. This figure can be easily increased by using a higher drive voltage. This shows that the system is capable of supplying sufficient power to wireless SHM sensor nodes, which currently have a maximum power requirement of approximately 200 mW.

The thermoelectric dimensionless figure-of-merit, ZT, which consists of the Seebeck coefficient, , electrical resistivity,  and thermal conductivity, , is an important parameter that characterizes the energy conversion performance of thermoelectric materials and devices. Larger ZT indicates higher performance of thermoelectric device. Current techniques for determining ZT involve measurements of ,  and  individually or ZT directly, but all techniques are carried out under a small temperature difference (T). In reality, a thermoelectric device generally operates under a much larger T and with an electrical current flowing through the thermoelectric materials. Clearly, ZT values are conventionally evaluated under a condition which differs significantly from the real operating conditions of thermoelectric devices. Recently, a novel principle for ZT measurement has been proposed, which has the capability of measuring ZT values under a large T and with an electrical current flowing through the samples. The main objective of the research embodied in this thesis is to investigate experimentally the feasibility of the proposed technique and subsequently to develop a laboratory measurement system for thermoelectric materials research. The feasibility of the proposed technique was investigated initially using thermoelectric modules. The results show a reasonable agreement with conventional techniques when it is used to measure ZT under a small T. Furthermore, the investigation reveals that ZT obtained under a large T differ significantly from those obtained under a small T. This confirms the unique capability of the proposed technique. The implementation of this technique for measuring the ZT of thermoelectric materials has proved to be very challenging due to the low electrical resistance (< 0.01 ) of the material samples. Following an in-depth experimental and theoretical investigation, a new design with a modified operating principle was proposed and carried out. The measurement system based on this new design was successfully developed, which has the capability of measuring single materials with different dimensions and under a larger T. The performance of this system was investigated using a standard Bi2Te3 sample as the reference for calibration. The results show that the system has a repeatability of <10% and an accuracy of 13-32%. Investigation on single materials and segmented structures showed that there were noticeable differences between a small and a large T, which can be attributed to the Thomson effect and changes in  values. This finding contributes to an improved understanding and new knowledge of thermoelectric behaviour under a large temperature difference. The measurement technique developed in this work will provide a useful tool for investigation and for the optimization of advanced thermoelectric structures.