Any form of paralysis due to spinal cord injury or other medical condition, can have a significant impact on the quality and life expectancy of an individual. Advances in medicine and surgery have offered solutions that can improve the condition of a patient, however, most of the times an individual’s life does not dramatically improve. Implanted neuroprosthetic devices can partially restore the lost functionalities by means of functional electrical stimulation techniques. This involves applying patterns of electrical current pulses to innervate the neural pathways between the brain and the affected muscles/organs, while recording of neural information from peripheral nerves can be used as feedback to improve performance. Recording naturally occurring nerve signals via implanted electrodes attached to tripolar amplifier configurations is an approach that has been successfully used for obtaining desired information in non-acute preparations since the mid-70s. The neural signal (i.e. ENG), which can be exploited as feedback to another system (e.g. a stimulator), or simply extracted for further processing, is then intrinsically more reliable in comparison to signals obtained by artificial sensors. Sadly, neural recording of this type can be greatly compromised by myoelectric (i.e. EMG) interference, which is present at the neural interface and registered by the recording amplifier. Although current amplifier configurations reduce myoelectric interference this is suboptimal and therefore there is room for improvement. The main difficulty exists in the frequency-dependence of the electrode-tissue interface impedance which is complex. The simplistic Quasi-Tripole amplifier configuration does not allow for the complete removal of interference but it is the most power efficient because it uses only one instrumentation amplifier. Conversely, the True-Tripole and its developed automatic counterpart the Adaptive-Tripole, although minimise interference and provide means of compensating for the electrode asymmetries and changes that occur to the neural interface (e.g. due to tissue growth), they do not remove interference completely as the insignificant electrode impedance is still important. Additionally, removing interference apart from being dependent on the frequency of the interfering source, it is also subject to its proximity and orientation with respect to the recording electrodes, as this affects the field. Hence neutralisation with those two configurations, in reality, is not achieved in the entire bandwidth of the neural signal in the interfering spectrum. As both are less power efficient than the Quasi-Tripole an alternative configuration offering better performance in terms of interference neutralisation (i.e. frequency-independent, insensitive to the external interference fields) and, if possible, consume less power, is considered highly attractive. The motivation of this work is based on the following fact: as there are models that can mimic the frequency response of metal electrodes it should be possible, by constructing a network of an equivalent arrangement to the impedance of electrodes, to fit the characteristic neutralisation impedance – the impedance needed to balance a recording tripole – and ideally require no adjustment for removing interference. The validity of this postulation is proven in a series of in-vitro preparations using a modified version of the Quasi-Tripole made out of discrete circuit components where an impedance is placed at either side of the outer electrodes for balancing the recording arrangement. Various models were used in place of that impedance. In particular, representing the neutralisation impedance as a parallel RC reduced interference by a factor of 10 at all frequencies in the bandwidth of the neural signal while removed it completely at a spot frequency. Conversely, modelling the effect of the constant phase angle impedance of highly polarisable electrodes using a 20 stages non-uniform RC ladder network resulted in the minimisation of interference without the initial requirement of continuous adjustment. It is demonstrated that with a model that does not perfectly fit the impedance profile of a monopolar electrochemical cell an average reduction in interference of about 100 times is achieved, with the cell arranged as a Wheatstone bridge that can be balanced in the ENG band.

This thesis presents a novel concept of beam scanning and forming by employing frequency diversity in an array antenna. It is shown that by applying a linear frequency shift to the CW signals across the elements, a periodically scanning beam pattern is generated and the main beam direction is a function of time and range. Moreover, when transmitting a pulse signal, the frequency diversity array (FDA) can be used for beam forming in radar applications. These properties offer a more flexible beam scanning and forming option over traditional phase shifter implementations. The thesis begins with the discussion on FDA’s array factor. It is mathematically proven that the array factor is a periodic function of time and range and the scanning period itself is a function of the linear frequency shift. Then further discussion is made when a pulsed signal is transmitted by an FDA. The requirement on the pulse width for a certain linear frequency shift is specified and corresponding signal processing technique is provided for the frequency diverse signal receiver. The thesis subsequently goes on to an electromagnetic simulation of FDA. The CST Microwave Studio is utilized to model the FDA and simulate its transient field, which allows one to verify the relationship between the scanning period and the linear frequency shift. Finally, the implementation of FDA is considered with the focus laid on the generation of the required frequency diverse signals complying with the two basic assumptions. The PLL frequency synthesis technique is introduced as an effective approach of generating the frequency diverse signals. One low cost and profile design of integer-N frequency synthesizer is presented to illustrate the basic design considerations and guidelines. For comparison, a Σ − Δ fractional-N frequency synthesizer produced by Analog Device is introduced for designs where more budget is available.

This thesis reports on research into the field of multiband Passive Bistatic Radar (PBR). The work is based on the premise that it is possible to improve on the PBR range resolution by exploiting the full broadcasted bandwidth from transmitters of opportunity. This work comprises both Frequency Modulated (FM) radio and Digital Video Broadcast - Terrestrial (DVB-T) waveforms. The work shows how the exploitation of the available frequency scattered bandwidth broadcasted from single broadcast towers can be achieved by coherently by combining each of the individual channels/bands, and that the range resolution is improved accordingly. The major contributions of this thesis may be divided into the following parts: Hardware (HW) design and development, algorithm development, simulations, real target data analysis, and finally non-cooperative target recognition and High Range Resolution (HRR) considerations. The work comprises simple PBR performance predictions for various strong transmitters of opportunity in the southeastern parts of Norway. Hardware for data recording was designed, produced and made working. The mathematics for coherently combining non-adjacent single channels/bands in the range correlation was developed. The range resolution performance of the algorithm was supported by theoretical simulations using pseudo random generated signals, as well as simulations using real recorded FM radio and DVB-T signals from nearby strong transmitters. For FM radio and DVB-T airliners and for DVB-T also a propeller aircraft were analyzed. The theoretical claims were supported by the real life target analysis, as the range resolution was improved as predicted for all targets. For the DVB-T waveform, an analysis of the HRR profiles showed that two targets of different type was manually classified as targets of different type. This work has fully closed the circle from idea, HW design, development and testing, theoretical algorithm development and simulations, and finally real world performance analysis as well as target analysis.

Electrodes at the Brain Machine Interface (BMI) must fulfil tall specifications: They must have excellent electrical properties to transduce electrogenic activity, be highly biocompatible and not degrade in a saline environment over the lifetime of the patient. In this respect, diamond is an excellent BMI material. In this thesis, the application of diamond at the BMI is investigated. Results Chapter 5 discusses the use of nanodiamond (ND) monolayers to promote the formation of functional neuronal networks. Neurons cultured on ND-coated substrates perform remarkably well, and similar to those grown on standard protein-coated materials with respect to their initial cell attachment, outgrowth, neuronal excitability and functionality of the resulting networks. NDs bypass the necessity of protein coating and show great potential for chronic medical implants. Chapter 6 describes the fabrication of nanocrystalline diamond (NCD) Micro-Electrode Arrays (MEAs) for the recording of electrogenic cells. MEAs are fabricated with metallic boron-doped nanocrystalline diamond (BNCD) and passivated with NCD, SiO2/Si3N4/SiO2 stacks and SU-8 epoxy. The recording of electrogenic activity of HL-1 cardiac cells is demonstrated with high signal-to-noise ratios and low signal loss. Chapter 7 and Chapter 8 describe the development of boron-doped (111) diamond Solution Gate Field-Effect Transistors (SGFETs). In Chapter 7 an optimised Plasma Enhanced Chemical Vapour Deposition (PECVD)-doping recipe using the (111) diamond plane is presented. AC Hall characterisation yields desirable sheet carrier densities for FET application with enhanced carrier mobilities, and Impedance Spectroscopy (IS) measurements divulge metallic electrical properties with low activation energies, indicative of heavily doped diamond as confirmed by Secondary Ion Mass Spectroscopy (SIMS). Chapter 8 describes the fabrication of boron δ-doped (111) diamond SGFETs (δ-SGFETs). δ-SGFETs show improved I-V characteristics in comparison to previous similar devices, whereby the enhancement mode operation, channel pinch-off and current saturation are achieved within the electrochemical window of diamond. Considering the biocompatibility of diamond towards cells, δ-SGFETs are promising for recording electrogenic cells.

Optical orthogonal frequency division multiplexing (O-OFDM) is a potential candidate for 100 Gigabit Ethernet (GbE) and beyond due to its high spectral efficiency and strong resilience towards chromatic and polarization mode dispersion. In this thesis, investigations have been performed into the feasibility of O-OFDM in high speed optical fibre communications. First, an overview of OFDM fundamentals and optical fibre communications is given. Numerical simulations which were performed to characterise and optimise real-time OFDM transceivers are then presented. The effects of a variety of design parameters on the performance of the system are studied. Amongst the key parameters included in the study are the quantisation and clipping noise in data converters, and the quantisation errors in the fast Fourier transform and its inverse (FFT/IFFT). Optimum parameters that give the best trade-off between performance and cost in terms of bit precision are determined. It was found that these parameters depend on the modulation format as well as the size of the FFT used in the system. The thesis then presents the design of a multi-gigabit real-time O-OFDM transmitter based on field programmable gate array (FPGA) implementation. The 21.4 GS/s real-time transmitter was built and used to transmit 8.36 Gb/s directly-detected single sideband QPSK-OFDM signals over 1600 km of uncompensated standard single mode fibre. This was one of the first demonstrations of real-time OFDM transmitters operating at such high line rates. It remains the longest transmission distance achieved with a real-time OFDM transmitter. The next step in confirming the feasibility of O-OFDM involves the design and assessment of application-specific integrated circuit (ASIC) implementations. In the final part of the thesis, digital signal processing (DSP) circuits for 21.8 Gb/s and 43.7 Gb/s QPSK- and 16-QAM-encoded O-OFDM transceivers with 50 data subcarriers were designed at the register-transfer-level, and synthesis and simulations were carried out to assess their performance, power consumption, and chip area. The aim of the study is to determine the suitability of OFDM technology for low-cost optical interconnects. Power calculations based on synthesis for a 65nm standard-cell library show that the DSP components of the transceiver consume 18.2 mW/Gb/s and 12.8 mW/Gb/s in the case of QPSK and 16-QAM respectively. The effects of modulation format and FFT size on the area and power consumption of the transceivers are also quantified. Finally, characterisation results showing the trade-offs between energy consumption and chip footprint are presented and analysed to help designers optimise the transceivers according the requirements and specifications.

The work presented herein explores the use of digital coherent receivers in loss limited transmission with a view to implementation in a 100 km long-reach passive optical network (LR-PON) with a net data rate of 10 Gbit/s per optical network unit. Optical power receiver sensitivity limits are investigated for C-band coherent receivers. Coherent-enabled advanced (amplitude, phase, and polarisation) modulation schemes are characterised in terms of electronic and optical bandwidth requirements and power efficiency to determine the optimum modulation format for a high capacity LRPON. Including the net coding gain achievable with forward error correction, the high power efficiency of polarisation switched (PS) quadrature phase shift keying (QPSK) enables an experimental demonstration of 4 photons/bit receiver sensitivity, while polarisation division multiplexed (PDM) QPSK enables transmission with 5 photons/bit sensitivity; a 0.5 dB power penalty. Nevertheless, PDM-QPSK is identified as the optimum modulation format for coherent LR-PON, due to its 1.25 dB bandwidth efficiency advantage over PS-QPSK. A coherent access network architecture is developed using 10 Gbit/s PDM-QPSK channels in a wavelength division multiplexed configuration. Multiple access is achieved by using the frequency selectivity of the coherent receiver to provide gain to the channel of interest. Combined with high receiver sensitivity, this demonstrates the feasibility of colourless network operation supporting 1024 channels. In bidirectional transmission, crosstalk from backscattering of optical power is mitigated using the receiver frequency selectivity and by using pulse shaping to restrict the optical channel bandwidth. A reflection-to-signal power ratio of 18.5 dB is tolerated without penalty. Practical realisation is addressed by exploring low complexity, multiplier-free digital signal processing (DSP) algorithms for adaptive channel equalisation; algorithms are identified that can be used without penalty. Finally, to address issues of integration, tunable local oscillator lasers, suitable for monolithic integration, are investigated. The receiver DSP is modified to overcome the additional intensity noise from these lasers. In this scenario, the reduced receiver sensitivity would still enable an LR-PON with 128 channels.

This thesis considers some of the requirements and challenges in the eld of organic thin lm transistors (OTFTs), from the standpoint of large scale integration using low temperature plastic compatible processes. A combination of processes and materials for use in the fabrication of OTFTs is developed, yielding device performance comparable with the state of the art for bottom-contact, bottom-gate, organic small molecule thin lm transistors. High quality silicon nitride (SiNx) gate dielectric material is developed using plasma enhanced chemical vapour deposition (PECVD) at a low temperature (150 C) compatible with plastic substrates. A variety of high quality lms are developed, allowing an investigation into the impact of changes in SiNx composition on OTFT performance. Surface modi cation strategies on SiNx substrates are considered, leading to almost an order of magnitude enhancement in OTFT performance, suggesting a suitable device architecture for large scale integration, and exploitation of novel organic material properties. We then examine organic semiconductor nanowire devices, which have begun to emerge as a new and exciting class of device in recent years. This work explores the possibilities of combining traditional thin lm transistor fabrication techniques with novel organic nanowires and examines the resultant transistor device behaviour. Two-dimensional arrays of nanowire devices are analysed, demonstrating the suitability of devices for large area applications. The combination of a large area and plastic compatible, low temperature dielectric with well known organic semiconductors in thin lm devices suggests that the integration of novel organic nanowires could provide an exciting performance enhancement over traditional OTFT devices.

In order to meet the requirements of emerging services, the future Internet will need to be flexible, reactive and adaptive with respect to arising network conditions. Network management functionality is essential in providing dynamic reactiveness and adaptability but current management approaches have limitations which prevent them from meeting these requirements. In search for a paradigm shift, recent research efforts have been focusing on autonomic/self-management principles, whereby network elements can adapt themselves to contextual changes without any external intervention through adaptive and flexible functionality. This thesis investigates how autonomic principles can be extended and applied to fixed networks for quality of service and performance management. It presents a novel resource management framework which enables intelligence to be introduced within the network in order to support self-management functionality in a coordinated and controllable manner. The proposed framework relies on a distributed infrastructure, called the management substrate, which is a logical structure formed by the ingress nodes of the network. The role of the substrate is illustrated on realistic resource management application scenarios for the emerging self-managed Internet. These cover solutions for dynamic traffic engineering (load balancing across multiple paths), energy efficiency and cache management in Internet Service Providers. The thesis addresses important research challenges associated with the proposed framework, such as the design of specific organisational, communication and coordination models required to support the different management control loops. Furthermore, it develops, for each application scenario, specific mechanisms to realise the relevant resource management functionality. It also considers issues related to the coexistence of multiple control loops and investigates an approach by which their interactions can be managed. In order to demonstrate the benefits of the proposed resource management solution, an extensive performance evaluation of the different mechanisms described in this thesis have been performed based on realistic traffic traces and network topologies.

Distribution of IEEE 802.11a Wireless Local Area Networks (WLAN) using wireless over fibre (WOF) technology have been achieved by employing novel InP based Asymmetric Fabry-Perot Modulator/detectors (AFPM) with quaternary material system InGaAs/AlInGaAs Multiple Quantum Wells (MQW). The Quantum-Confined Stark Effect (QCSE) electroabsorption AFPM operates simultaneously as an optical intensity modulator on the uplink and as a conventional photodetector on the downlink. In this work, the design and fabrication of the new InGaAs/AlInGaAs MQW AFPM device is developed and discussed. The electrical and optoelectronic characterisation of the AFPM shows an improved modulation slope –dR/dV of over 40 %/V, where dR is the differential optical reflectance and dV is the differential terminal voltage, compared to the previously reported 6-10 %/V achieved with an InGaAsP/InGaAsP MQW AFPM. The modulation bandwidth exceeds 18 GHz, hence verifying the feasibility of the AFPM for integration with an Electromagnetic Band Gap (EBG) antenna to perform data transmission in real environments. The design and integration processes of the EBG photonic antenna are described. In addition, the first bi-directional link and IEEE802.11a WLAN data transmission experiments using EBG photonic antenna and 2 x 2 photonic array antennas with integrated InGaAs/AlInGaAs MQW AFPMs are reported and compared with uncooled directly modulated lasers. Half-duplex IEEE 802.11a connection was successfully established between a laptop computer and the photonic antenna, which in turn was connected via an optical fiber to a wireless access point. A maximum data throughput of 7 Mbps was achieved at 8 m separation between the laptop and the photonic antenna.

This thesis is concerned with the generation of Continuous Wave Terahertz signals from photomixing sources based on the InP material system. Continuous Wave systems are expected to dominate future Terahertz technology where agile, high resolution systems are required. Photomixing offers a low cost and compact solution for broadband Terahertz systems. Driven by the established Telecommunications industry, the InP material system has numerous devices to offer operating at 1550 nm. In this thesis the Travelling-Wave Uni- Travelling Carrier Photodiode (TW-UTC-PD) is proposed as a novel photomixing element that combines the advantages of other previously demonstrated devices. The theory of ultra-fast photodetectors is studied thoroughly and theoretical considerations towards advanced InP-based photodetectors are given. A figure of merit for the Photonic-to-Terahertz conversion efficiency is defined here. In order to maximise this efficiency different input optical waveguides and output planar antennas are studied. A semi-analytical model that predicts the frequency response and the efficiency is developed as an essential tool for the design of these devices. TW-UTC-PDs integrating a mode converting optical waveguide and two types of output configurations were fabricated. Devices with a Coplanar Waveguide output were tested at DC and in the millimetre-wave range. DC responsivities of up to 0.53 A/W at 1550 nm were achieved together with a 3-dB bandwidth of 105 GHz. The same devices demonstrated an output power of 1 mW at 200 GHz. Antenna integrated devices achieved 40 μW at 510 GHz, 5 μW at 1.02 THz and 0.5 μW at 1.53 THz at a photocurrent of 13 mA when pumped with less than 40 mW of optical power. Packaged devices showed broadband response up to 1 THz. The achievements described in this thesis are anticipated to play an important role towards Continuous Wave photomixing Terahertz systems based on InP-based components. In combination with recent demonstrations of detection of millimetre-wave signals with the same device, efficient and compact spectroscopic and communication systems based on the TW-UTC-PD that are also capable of a high degree of photonic integration should be feasible.