The perceptual characteristics of a microphone are not always clear from its technical specification. This thesis documents a first step towards creating more perceptually relevant measures. Consideration of relevant criteria revealed that the most appropriate method for recording stimuli for perceptual microphone comparisons is to use all microphones under test simultaneously. Experiments determined that a maximum array size of 150 mm will ensure that the perceptual differences between the recorded stimuli are predominantly due to the characteristics of the microphones and not artefacts of the spacing between them. It was established that there are eight standard physical differences that exist between microphones which may impact the perceived characteristics of a recording. These differences, supplemented with expert opinions, indicated that recording five programme items with eight studio and two MEMS microphones would allow for determination of the most prominent inter-microphone perceptual differences. A combination of indirect and direct elicitation experiments on the resulting 50 recordings identified a hierarchy of 40 perceptual attributes that describe the differences between microphones. A novel attribute contribution experiment conducted on the 31 lowest-level attributes in the hierarchy showed that brightness contributes the most overall to the inter-microphone difference. The spectral centroid and ratios comparing the relative level of high frequencies were previously used to predict brightness; however, these metrics did not predict subjective ratings of microphone-related brightness as well as a newly proposed combination metric: the product of the spectral centroid above 3 kHz, and the ratio of energy above 3 kHz compared to all energy. This model performed well on training data (r = 0.909). Validating it on independent microphones and programme items suggested that improvements may be necessary for error-free prediction of programme-related aspects of brightness, but showed good correlation with each programme item and overall (r = 0.854), indicating that the model predicts microphone-related brightness well.

Next-generation electronic devices which are cheap, lightweight and flexible could be realised through the use of solution processable organic polymer and small molecule semiconductors. Unlike inorganic semiconductors such as silicon, soluble organic semiconductors could be processed using traditional high through-put printing techniques such as roll-to-roll processing and ink-jet printing, which would dramatically reduce manufacturing costs. Whilst organic semiconductors are not expected to be as high performance as inorganic semiconductors, improvements in performance are still required before commercialisation is possible. One way to help improve performance is to exploit the chemical versatility of organic materials. Many different structures can be synthesised through chemical modification, allowing the optoelectronic properties (such as the optical band gap and energy levels) and physical properties (such as solid state structure) of the material to be tuned. Materials can therefore be chemically designed to optimise their performance in organic electronic devices. This work is focused on exploring the relationship between chemical structure, material properties and device performance, through the design and synthesis of new materials for organic field-effect transistors (OFET) and organic photovoltaics (OPV). The majority of the new materials synthesised in this thesis are new donor-acceptor polymers (Chapters 2-6), in which an electron donating monomer and electron accepting monomer are co-polymerised. Whilst there is a vast wealth of different donor monomer structures available, there has been less focus on the synthesis of new electron accepting monomers. In this work the common electron acceptor monomer 2,1,3-benzothiadiazole (BT) is chemically modified to either increase the solubility (Chapter 2) or increase the electron accepting strength (Chapters 3 and 4). Increasing the strength of the electron accepting unit in donor-acceptor polymers was found to induce N-type (electron conducting) behaviour in OFET devices (Chapter 3) or improve OPV performance by reducing the optical band gap and increasing light absorption (Chapter 4). Power conversion efficiencies of ~6.5% in OPV devices were achieved. In chapter 6 a novel BT based acceptor monomer is designed to maximise polymer backbone planarity which resulted in promising hole mobilities of up to 0.5 cm2/Vs when tested in OFET devices. In Chapter 5 the strength of the common electron accepting unit benzo[d][1,2,3]thiadiazole (BTz) is also increased through chemical modification. Similarly to Chapter 4, we find that increasing the strength of the electron accepting unit of the donor-acceptor polymer improves the OPV performance through increased light absorption, resulting in efficiencies of ~6.5% in OPV devices. Finally in Chapter 7, new electron rich conjugated small molecules are synthesised and the optoelectronic properties investigated.

This thesis explores the possibilities of the design and realization of compact conventional and substrate integrated waveguide structures with improved performance taking advantage of recent cross-coupled resonator filters theory achievements such as the modular filter design approach using non-resonating nodes and inline extracted pole filters. Therefore, the core of the thesis presents the following stages of work: -- Solution of electromagnetic problem for wave propagation in rectangular waveguide structures; overview of substrate integrated waveguides. -- Review of available design procedures for cross-coupled resonator filters; realization of coupling matrix synthesis methods by optimization. -- Investigation of the possibility to implement filtering modules using E-plane metallo-dielectric inserts in conventional rectangular waveguides. Application of the modules in configurations of bandpass and dual-band filters. Experimental verification of the filters. -- Implementation of inline extracted pole filters using E-plane inserts in rectangular waveguides. Use of generalized coupling coefficients concept for individual or coupled extracted pole sections. Development of new extracted pole sections. Application of the sections in the design of compact cross-coupled filters with improved stopband performance. -- Application of the techniques developed for conventional rectangular waveguides to substrate integrated technology. Development of a new negative coupling structure for folded substrate integrated resonators. Design of improved modular and extracted pole filters using substrate integrated waveguides.

In this thesis, novel analog-to-digital and digital-to-analog generalized time-interleaved variable bandpass sigma-delta modulators are designed, analysed, evaluated and implemented that are suitable for high performance data conversion for a broad-spectrum of applications. These generalized time-interleaved variable bandpass sigma-delta modulators can perform noise-shaping for any centre frequency from DC to Nyquist. The proposed topologies are well-suited for Butterworth, Chebyshev, inverse-Chebyshev and elliptical filters, where designers have the flexibility of specifying the centre frequency, bandwidth as well as the passband and stopband attenuation parameters. The application of the time-interleaving approach, in combination with these bandpass loop-filters, not only overcomes the limitations that are associated with conventional and mid-band resonator-based bandpass sigma-delta modulators, but also offers an elegant means to increase the conversion bandwidth, thereby relaxing the need to use faster or higher-order sigma-delta modulators. A step-by-step design technique has been developed for the design of time-interleaved variable bandpass sigma-delta modulators. Using this technique, an assortment of lower- and higher-order single- and multi-path generalized A/D variable bandpass sigma-delta modulators were designed, evaluated and compared in terms of their signal-to-noise ratios, hardware complexity, stability, tonality and sensitivity for ideal and non-ideal topologies. Extensive behavioural-level simulations verified that one of the proposed topologies not only used fewer coefficients but also exhibited greater robustness to non-idealties. Furthermore, second-, fourth- and sixth-order single- and multi-path digital variable bandpass digital sigma-delta modulators are designed using this technique. The mathematical modelling and evaluation of tones caused by the finite wordlengths of these digital multi-path sigmadelta modulators, when excited by sinusoidal input signals, are also derived from first principles and verified using simulation and experimental results. The fourth-order digital variable-band sigma-delta modulator topologies are implemented in VHDL and synthesized on Xilinx® SpartanTM-3 Development Kit using fixed-point arithmetic. Circuit outputs were taken via RS232 connection provided on the FPGA board and evaluated using MATLAB routines developed by the author. These routines included the decimation process as well. The experiments undertaken by the author further validated the design methodology presented in the work. In addition, a novel tunable and reconfigurable second-order variable bandpass sigma-delta modulator has been designed and evaluated at the behavioural-level. This topology offers a flexible set of choices for designers and can operate either in single- or dual-mode enabling multi-band implementations on a single digital variable bandpass sigma-delta modulator. This work is also supported by a novel user-friendly design and evaluation tool that has been developed in MATLAB/Simulink that can speed-up the design, evaluation and comparison of analog and digital single-stage and time-interleaved variable bandpass sigma-delta modulators. This tool enables the user to specify the conversion type, topology, loop-filter type, path number and oversampling ratio.

This work is a pioneer study on the role played by molecular interfaces in altering the electronic states of non-ferromagnetic materials. Here, we consider diamagnetic copper and paramagnetic manganese and scandium, to overcome the Stoner criterion and make them magnetically ordered at room temperature. The mechanism is mediated by the charge transfer from the transition metal and hybridization with molecular carbon, creating new 3d-π that drastically modify the electron energy bands around the Fermi energy of both metal and molecule. This effect is achieved via interfaces between metallic thin films and C60 molecular layers. The emergent spin ordering arising in these systems is measured using magnetometry shows magnetically ordered behaviour at room temperature, but dependent on the thickness and continuity of the metallic layer. To determine how in the layered structure the emergent spin ordering is distributed, low-energy muon spin spectroscopy is utilised by studying the depolarization process of low-energy muons implanted in the sample. This technique indicates localised spin-ordered states at, and close to, the metallo-molecular interface. X-ray absorption spectroscopy provides an excellent tool for identifying the emergent spin ordering of specific elements within a sample. The change in the molecular orbitals of C60 due to charge transfer and 3d-π hybridization is evaluated based on this technique. The presence of spin ordering in a non-magnetic metallic host due to molecular charge transfer has a drastic effect not only on the magnetic but also on the transport properties of the system. The decisive role of the molecular interfaces in the physics of spin dependent scattering within a non-magnetic host has been demonstrated. Localised spin ordering leads to changes in the Kondo and weak localisation effects with applications in low temperature thermometry and quantum devices. It is found that there is an additional magnetic scattering that has a pronounced contribution when C60 molecules are embedded into the non-magnetic Cu and hence creates localised spins. The localised spin ordering that emerged at molecular interfaces is a new approach for novel generation of materials for future spintronics devices.

This thesis extensively explores, for the first time, the technical feasibility and performance of real-time end-to-end optical orthogonal frequency division multiplexing (OOFDM)transmission systems by implementing field programmable gate array (FPGA)-based OOFDM transceivers incorporating entirely self-developed digital signal processing (DSP)algorithms. Commercially available 4GS/s, 8 quantization-bit digital-to-analogue (DAC) and analogue-to-digital converters (ADC) are utilised in the transceivers and low-cost intensity modulation and direct detection (IMDD) transmission systems are also employed for all transmission systems as the research focuses on cost-sensitive access and inbuilding networks. A series of world–first and world-only, real-time, end-to-end OOFDM transmission systems were achieved. The initial DQPSK-based transceiver designs demonstrated first a 1.5Gb/s and subsequently a 3Gb/s net bit rate over 500m multi-mode fibres (MMFs). Thorough enhancement of the transceiver‟s DSP design, 16-quadrature amplitude modulation (16-QAM) with additional DSP features achieved a 6Gb/s net bit rate over 300m MMF, followed by an 11.25Gb/s line rate over 500m MMFs and 25km standard single-mode fibres (SSMFs) /MetroCore™ SMFs due to the utilisation of 64-QAM with more advanced DSP functions. The use of different intensity modulators, as alternatives to the initial DFB-based directly modulated laser (DML), was explored. A colourless OOFDM transceiver was demonstrated at 7.5Gb/s line rate over 25km SSMF using a 1GHz reflective semiconductor optical amplifier (RSOA) as an intensity modulator. To further reduce the transceiver cost, a low-cost VCSEL-based DML was successfully employed at 11.25Gb/s over 25km SSMF. To achieve a fully autonomous OOFDM receiver a synchronous clocking technique was proposed and experimentally demonstrated at 11.25Gb/s over 25km SSMF without degradation in system performance. Over the same IMDD systems, a versatile, highly accurate, performance penalty-free solution for automatic symbol synchronisation was also proposed and experimentally demonstrated using DC offset signalling. This research is a significant milestone in proving the technical feasibility of OOFDM for practical applications in future access and in-building networks.

This thesis concerns the processing and characterization of thick PZT sol-gel films for potential applications in MEMS devices. The deposition method was spin-coating. The aim was to reduce the number of coatings in the film processing by increasing the thickness of a single coating, with the restriction that the processed films must be crackfree and dense. Only by retaining the thick film dense, pore-free and crack-free one can obtain the piezoelectric properties in thick films that make the PZT thin sol-gel films attractive for the MEMS applications. Three PZT compositions, PZT 40/60, PZT 60/40 and PZT 52/48 were investigated. Each one of these PZT compositions has different crystallographic structure and thus differences in the piezoelectric properties were expected. The processing of thickness-increased sol-gel films was investigated. A combination of analysis techniques was employed. The stress development was monitored via ex-situ wafer deflection measurement after various fabrication steps. The ongoing processes in the sol-gel film were identified and correlated to certain temperature ranges and to the stress that is induced with each process in the film. It was found that crack-free films could be fabricated if a stress-controlled heating profile was applied. The PZT films were deposited on platinised silicon substrate and it was found that stress-related recrystallization was taking place in the platinum electrode which affected the total stress. After the platinum recrystallization the stress state in the bottom electrode and in the substrate was stable. Films up to 5 μm thick were obtained by repeated deposition of 200 nm thick single layers. The maximum thickness of a single coating was increased to 500 nm and a 2.5 μm film was fabricated by only 5 repeated coatings. The crystallographic orientation of all three employed PZT compositions was studied systematically on Pt/Si substrate at different thicknesses. Also, individual PZT films were deposited onto platinised sapphire substrates, or on LNO/Si substrate. It was found that the orientation of the films changes gradually with each coating. The residual stresses in all three PZT compositions were studied. A stress model for composite structures was applied for the first time in PZT films stress analysis. The results have shown that the residual stress at the room temperature is due to thermal expansion mismatch between the individual layers. Furthermore, a large orientation dependent stress variation was found in PZT 52/48 films that could be only explained if anisotropic thermal expansion in PZT were considered. The lattice parameters of all PZT compositions were determined and were in good agreement with the residual stress results. Thus, using the stress model it was possible to understand the origin of stress in PZT films. Finally, the electrical properties of the PZT films were determined. It was found that the piezoelectric, dielectric and ferroelectric properties of PZT films vary with PZT composition, film thickness and depend on the substrate type. Based on the finding it was proposed that there must be an interfacial layer that is responsible for domain wall pinning and thus reduced PZT properties in films below 5 μm thickness. In thick PZT 40/60 films enhanced piezoelectric properties were found making these PZT compositions very promising candidates for MEMS application.

Molecular electronics based on the bottom-up approach appears to be a promising alternative to overcome the limitations of the top-down lithographic fabrication of electronic devices. The ability to manipulate single or small groups of molecules provides a great opportunity to build electronic devices at the molecular level. However, before any device can be constructed, it is vital to understand the parameters that control the device properties such as: molecular structure, conformation and arrangement at the surface, the molecule-substrate and molecule-electrode interactions. This thesis presents an investigation of the alignment of acceptor-electron bridge-donor structures and describes how the molecular structure and arrangement affect rectifying properties of the monolayers. Studies included typical Langmuir-Blodgett (LB), chevron-shaped, and ionically coupled structures that were characterised using various techniques, such as Quartz Crystal Microbalance (QCM), Surface Plasmon Resonance (SPR), Second Harmonic Generation (SHG) and Scanning Tunnelling Spectroscopy (STS). The results obtained showed that to achieve high rectification the molecules must form ordered and stable monolayers that are able to withstand the electric field applied to the junction. It was also shown that due to the disordered monolayer formation and presence of certain ions, it was extremely difficult to state without doubt whether the rectification was a result of the donor-electron bridge-acceptor structure proposed by Aviram and Ratner1. Studies of chevron-shaped molecules confirmed the possibility of depositing them using the LB technique. However, the reduction of long aliphatic chains was very likely balanced by the formation of less ordered or unstable monolayers. The highest rectification ratio of 30 ± 3 at ± 1 V was obtained for 1-butyl-2,6-bis-[2-(4- dibutylamino-phenyl)-vinyl]-pyridinium iodide (dye 7) and the origin of the I-V asymmetry was attributed to back electron transfer from iodide to pyridinium ring. Although dye 1-butyl-2,6-bis-(2-{4-[2-(4-dibutylamino-phenyl)-ethyl]-phenyl}-vinyl)- pyridinium iodide (dye 9) showed electrical asymmetry (RR=16 at plus/minus 1 V) shortly after deposition onto the gold-coated highly oriented pyrolytic graphite (HOPG), it seemed to form an unstable alignment and as a consequence the rectification decayed over a period of a few hours. Improved ordering, stability, and rectification were achieved from ionically coupled structures, where the monolayers were formed using chemisorption and ionic assembly instead of physisorption.

Micro-assembly techniques have been identified as a major technology ‘pillar’ that will underpin further advancements in integrated micro-and nano-systems. In practice, there is a generic requirement for component parts that are often fragile, or that have been prepared by mutually incompatible processes, to be brought together to make a complete working system. This thesis discusses an electrostatic positioning technique for micro-scale elements that could form the basis of an industrial process. A highly non-uniform field generated between a needle-like upper electrode and a bottom flat electrode can be used to electrostatically capture, displace, and relocate elements into a predefined spatial configuration. The very intense field at the needle tip can facilitate the collection of the material at a precise point. However charge injection and local dielectric breakdown must also be considered as they can induce instability near the tip, and consequently interfere with any picking up action. The principal physical phenomena and potential benefits are analysed and discussed, considering three different configurations to achieve the pick and place operation for a micro-fibre in the needle-plane configuration. The first two are operated on an isolated single fibre lying on a flat bottom electrode, applying respectively a DC or an AC voltage. The third case is that of a group of fibres, and it exploits a dielectrophoretic chain structuring effect to assist in the micro-manipulation technique. Experimentation has focussed on the importance of the charge transfer mechanisms, leading to a model which provides good agreement with the observed behaviour. Moreover, an analysis of the forces exerted on the fibres showed that they arise not only from a polarisation effect, but that there is also an electrophoretic contribution. The viability of the proposed technique has been demonstrated using lead zirconate titanate (PZT rods and carbon fibres).

Following a review of previous work in this area, a presentation is made which illustrates the impact of a naive application of DVS in a system incorporating a time-triggered co-operative (TTC) scheduler. Novel algorithms (TTC-jDVS, TTC-jDVS2) and then introduced which more successfully integrate TTC and DVS techniques. These algorithms involve: (i) changes to system timer settings when the frequency is altered; (ii) use of a form of 'sandwich delay' to reduce the impact of changes to the scheduler overhead which arise as a result of frequency changes, and (iii) execution of jitter-sensitive tasks at a fixed operating frequency. The impact of these algorithms on both jitter and energy consumption is illustrated empirically on a representative hardware platform, using both 'dummy' task sets and a more realistic case study. In designs for which low jitter is an important consideration, at least a limited degree of task pre-emption may be required. A simple time-triggered hybrid (TTH) scheduler can be used to achieve such behaviour. A novel TTH secluding algorithm (TTH-jDVS) is presented and evaluated, again through use of dummy task sets and a case study. The third piece of experimental work presented in this thesis illustrates that --- in situations where minimal jitter is required --- hardware support is required. To illustrate the potential of such an approach a final case study is employed.