Frequency agile microwave devices based on Barium Strontium Titanate (BST) thin films have gained a lot of interest in recent years. The frequency agility of the ferroelectric devices is based on the external DC electric field controlled permittivity of BST thin film. In this research work, several tunable microwave filters incorporating BST thin film varactors operating in a frequency range between 1 GHz and 25 GHz are designed, tested and analysed. A lumped element lowpass filter incorporating integrated meander line inductors and BST parallel plate capacitors is implemented on a high resistivity silicon substrate and demonstrates 32.1 % tuning of the cut-off frequency at 15 V. A combline bandpass filter employing integrated BST parallel plate varactors as tuning elements is implemented on a MgO substrate and shows a reasonable tuning from about 8 GHz to 12 GHz with 10 V bias of only one resonator. Two pole and four pole coupled resonator bandpass filters with discrete BST or GaAs varactors as tuning elements are implemented in a frequency range of 1 - 3 GHz. The filters based on BST parallel plate capacitors show an insertion loss in line with the GaAs filters, which is also the lowest insertion loss of BST filters ever reported. Future work on improving the BST film and metal film loss at tens of gigahertz range is also discussed.

The work described in this thesis concerns the combining of wideband and reconfigurable narrow band functionality into a single antenna. This concept may be useful in reducing size and to give flexibility to a wireless terminal to operate in several different modes. The approach also offers additional pre-filtering to the front-end, which reduces the interference levels at the receiver, giving them a significant advantage over fixed non reconfigurable transceivers. Wideband-narrowband reconfiguration is potentially useful for future wireless communications such as software defined radio and cognitive radio, since they may employ wideband sensing and reconfigurable narrowband communications. Five novel reconfigurable antennas are presented. One is a switchable log periodic patch array and four are Vivaldi antennas with various forms of reconfiguration. The log periodic is reconfigured by placing switches between the patches and the feed line whilst the Vivaldi antenna has switched resonators controlling the current in the edges of the tapered slots. Wideband to various narrowband functions, wideband with a tunable band rejection having a very wide tuning ratio, and combined three function wide, narrow and tunable band rejection in a single antenna are demonstrated. Prototypes are presented with PIN diode switches, varactors, fixed capacitor or hard wire switches. Measured and simulated results with a very good agreement are presented, thus verifying the proposed concepts.

This thesis presents the first model of the electrical activity of the larval zebrafish heart as well as the design and fabrication of novel electrode arrays that were created to measure the electrocardiogram. The model consists of realistic 3D geometry of a 3 day’s post fertilisation zebrafish heart and body with a bidomain electrical model that uses the Fitzhugh-Nagumo equations as the ionic model. The model is able to replicate experimentally observed conduction velocities and action potentials by using region specific parameters and simulate electrocardiograms that are comparable to measurements. The electrode arrays are constructed from flexible polyimide films with gold microelectrodes. These devices have the potential to improve the measurement of the electrocardiogram for drug screening applications as an alternative to the use of micropipette electrodes. Gold plating and PEDOT:PSS coating techniques were applied to the devices to successfully reduce electrode impedance with the effectiveness of each technique categorised using impedance spectroscopy. The devices were tested in vivo with larval zebrafish with limited success and so in vitro tests were conducted using an artificial current source.

The research presented in this thesis concerns antenna designs based on metamaterial-inspired structures. Based on a review of the existing literature and understanding of the background theories, different metamaterial-inspired structures are applied to designs of resonant antennas (RAs) and leaky wave antennas (LWAs) for improved antenna characteristics. Extended composite right/left-handed (ECRLH) unit cell structures enable the RA designs with multiband or wideband properties; the novel metamaterial-inspired supercell structures enable the LWA designs with the dual-passband property and the backward-to-forward leaky-wave radiation characteristics in each passband. In addition, two tunable antennas are presented to mainly achieve the frequency reconfigurability and possibly the pattern reconfigurability by electronically controlling surface-mounted semiconductor varactors or discrete ferroelectric barium strontium titanium (BST) thin-film varactors. Furthermore, the uncertainty analysis in determination of permittivity of BST film materials from the characterization process is discussed in this thesis, in order to provide the design clues when the antenna with BST materials is designed. The conclusions are drawn and the possible future research directions are explained as well.

The advent of wireless body area networks (WBANs) and their use in a wide range of applications from consumer electronics to military purposes, dictates the need to investigate to the behaviour of antennas and wave propagation on the body in depth. Although this area has been extensively studied in the past decade, some issues are still not satisfactorily solved for communication systems for WBANs at ISM bands and UWB such as compact and high efficiency antenna design, privacy and security, interference mitigation and achieving high data rates. This thesis proposed an alternative wireless solution for body area networks by adopting 60 GHz radio. On-body channels at 60 GHz have been characterised using monopole and horn antennas. Horn antennas achieve significantly improved path gain in the stable channels but are susceptible to shadowing in the mobile channels due to body movements. However, interference mitigation and covertness for 60 GHz WBANs at the physical layer are improved due to high attenuation of 60 GHz signals. Significant increase of carrier-to-interference ratio is observed for 60 GHz WBANs compared to 2.45 GHz. A model of estimating the maximum detection distance at a threshold probability for detecting a WBAN wearing soldier in a battlefield is proposed. Fixed-beam directional antennas and reconfigurable antennas are designed for 60 GHz WBANs and channel measurements using these antennas are conducted. Results show beam-reconfigurability of the antenna improves the link performance compared to fixed-beam antennas at 60 GHz.

The effects of microstructure and prestraining and ageing on ductile-to-brittle transition temperature, fracture toughness and cleavage fracture resistance of a multi-pass low-alloy ferritic steel weld metal have been investigated. The weld metal simulated submerged arc welds used in the fabrication of Sizewell B power station reactor pressure vessel. The study aimed to investigate differences in mechanical properties of a single microstructure; asdeposited and reheated microstructures and subjected to various mechanical tests. Additionally, to simulate the effects of irradiation embrittlement a number of specimens were prestrained and then statically strain aged. Charpy impact transition curves had obvious trends depending upon microstructure and condition, with microstructure having a significant influence on the transition region and upper-shelf impact energy level. Prestraining and ageing the specimens promoted an increase in the ductile-to-brittle transition temperature and reduction the upper shelf energy level for both microstructures. The extremes of behaviour were defined by the reheated as-received and as-deposited prestrained and aged conditions, being the “best” and “worst conditions” respectively. This trend was repeated with the cracktip opening displacement tests. A combination of factors decreases toughness for the asdeposited prestrained and aged condition, which exhibited the highest yield stress, and lowest work hardening exponent and the best cleavage fracture resistance. Such factors result in marked upwards shifts in Charpy impact transition curves and decease in the crack growth resistance curves.

This thesis develops robustly feasible model predictive controllers (RFMPC) for nonlinear network systems and soft switching mechanism between RFMPCs is proposed to achieve softly switched RFMPC (SSRFMPC). The safety zones based technique is utilized to design RFMPC by two different mechanisms i.e. iterated safety zones or explicit safety zones. Although the former one is calculated online by the relaxation algorithm and its RFMPC achieve robust feasibility, the recursive robust feasibility is not guaranteed. In contrast to the former, the latter one is calculated off-line and its RFMPC achieves recursive robust feasibility. In addition to this, the robustly feasible invariant sets in the state space are calculated off-line and the initial states need to stay inside those invariant sets in order to achieve feasible control operation. The computation of RFMPC is very demanding and computing time is reduced by several methods. First, the more efficient optimization solver which is gradient type solver is used to solve the optimization task. The method to provide suitable gradients of objective function and derivatives of constraints to the optimization solver is presented. The robust output prediction is approximated and its horizon is also shortened. The optimization task is formulated in the reduced space of decision variables which is used in the implementation. The proposed methodology is verified by applying to a simulated drinking water distribution systems example. Comparative simulation results are presented and discussed.

An automatic analysis of bird vocalisations for the identification of bird species, the study of their behaviour and their means of communication is important for a better understanding of the environment in which we are living and in the context of environmental protection. The high variability of vocalisations within different individuals makes species’ identification challenging for bird surveyors. Hence, the availability of a reliable automatic bird identification system through their vocalisations, would be of great interest to professionals and amateurs alike. A part of this thesis provides a biological survey on the scientific theories of the study of bird vocalisation and corresponding singing behaviours. Another section of this thesis aims to discover a set of element patterns produced by each bird species in a large corpus of the natural field recordings. Also this thesis aims to develop an automatic system for the identification of bird species from recordings. Two HMM based recognition systems are presented in this research. Evaluations have been demonstrated where the proposed element based HMM system obtained a recognition accuracy of over 93% by using 3 seconds of detected signal and over 39% recognition error rate reduction, compared to the baseline HMM system of the same complexity.

Automatic synthesis of analogue circuits remains a very manually intensive task despite huge strides in the field of Electronic Design Automation (EDA) in recent decades. Genetic Algorithms (GAs) are biologically inspired search algorithms which have previously shown some promise in this field. Their ability to form the basis of a practically useful synthesis system is investigated. A GA-based experimental synthesis system is implemented, which employs a Genetic Programming (GP) style encoding scheme based on tree structures, and a novel fitness function based on pole-zero analysis. The system is capable of synthesising circuit topologies entirely from scratch, but can also utilise user-provided circuit knowledge of arbitrary detail and complexity. The system uses a SPICE-based circuit simulator as a circuit evaluator. Experimental results reveal a number of issues that adversely impact the ability of GAs to reliably synthesise practically useful analogue circuits. These include considerable resource requirements and a tendency for synthesised circuits to contain an unnecessarily large number of components. Most serious is the sensitivity of analogue circuits to changes in topology and/or sizing. GAs are shown to be currently ill-suited to the problem domain of analogue circuit synthesis. The problem of SPICE non-convergence on the GA is also considered.

As the mobile phone is an essential accessory for everyone nowadays, predistortion for the RF power amplifiers in mobile phone systems becomes more and more popular. Especially, new predistortions for power amplifiers with both nonlinearities and memory effects interest the researchers. In our thesis, novel predistortion techniques are presented for this purpose. Firstly, we improve the digital injection predistortion in the frequency domain. Secondly, we are the first authors to propose a novel predistortion, which combines digital LUT (Look-up Table) and injection. These techniques are applied to both two-tone tests and 16 QAM (Quadrature Amplitude Modulation) signals. The test power amplifiers vary from class A, inverse class E, to cascaded amplifier systems. Our experiments have demonstrated that these new predistortion techniques can reduce the upper and lower sideband third order intermodulation products in a two-tone test by 60 dB, or suppress the spectral regrowth by 40 dB and reduce the EVM (Error Vector Magnitude) down to 0.7% rms in 16 QAM signals, disregarding whether the tested power amplifiers or cascade amplifier systems exhibit significant nonlinearities and memory effects. i