Theses

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Included in the Research Theses collection are Masters, PHD and Professional Doctorate theses.
Masters and PHDs by coursework theses are included in the Honours and Coursework Theses collection. Some schools may choose to include Honours theses which make a significant contribution to knowledge.
If a school submits undergraduate theses or final year projects to the Digital Library, these will be included with the school's other collections.

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Open Access
Analysis of beat-to-beat QT interval variability in 12-lead ECG signals.
(2014) Hasan, Muhammad Asraful; Baumert, Mathias; Abbott, Derek; School of Electrical and Electronic Engineering
The human heart is a significant research topic in biomedical engineering due to the high incidence of heart disease in the developing world. Electrocardiography (ECG) is considered the primary diagnostic tool for the assessment of cardiac diseases and various heart arrhythmias. Note that ECG is the electrical representation of heart activity and can be recorded noninvasively by placing electrodes on the limbs and chest of the body. It is stated that certain heart diseases affect depolarization and repolarization. While the entire depolarization and repolarization of the heart is important, there is significant interest in the study and investigation of the ventricular depolarization and repolarization that is reflected by QT interval duration. The main reason for studying ventricular depolarization and repolarization is that some cardiac diseases, which are associated with ventricles of the heart, have an immediate effect on the body and can cause sudden cardiac death. Further, the knowledge of ventricular activation sequence and its abnormalities has contributed to our understanding of cardiac arrhythmias, but the underlying mechanisms and role of repolarization abnormalities is still not completely known. Therefore, this thesis presents several studies to explain more about the instability of repolarization duration in various cardiac patients by analysing different QT parameters. The main results of the thesis are: (i) Beat-to-beat QT interval variability (QTV) varies between the 12 standard ECG leads and caution should be paid when comparing beat-to-beat QTV results obtained from different leads across studies. (ii) The inter-lead correlation of beat-to-beat QTV is lead dependent. (iii) A negative correlation exists between beat-to-beat QTV and T-wave amplitude. (iv) No significant effect of mean heart rate, age and gender on beat-to-beat QTV in 12-lead resting ECG in healthy subjects. (v) An improved ECG-preprocessing technique is introduced and recommended for accurate measurement of beat-to-beat QTV. It substitutes the R-peak detection algorithm and implements an efficient baseline removal algorithm in the existing template matching approach. (vi) Effects of T-wave amplitude and ECG lead on beat-to-beat QTV in patients with Myocardial Infarction (MI) compared to healthy subjects are studied and suggest that increased beat-to-beat QTV in patients with MI is partly due to the lower T-wave amplitudes and some other unknown reason. (vii) The study also confirms that patients with MI have lower heart rate variability (HRV) compared to healthy subjects. (viii) Moreover, beat-to-beat QTV remains higher in patients with MI even after controlling the T-wave amplitudes. (ix) Two new beat-to-beat VCG (vectorcardiography) descriptors that have independent diagnostic attributes for assessing patient populations are introduced. (x) Overall spatial and temporal VCG descriptors may provide markers of electrical instability in the heart of patients with MI but need further research for the quantification and analysis of beat-to-beat VCG descriptors. (xi) Effect of pacing and pharmacologically induced autonomic nervous system modulation on VCG parameters and on beat-to-beat QTV is limited in heart failure patients. In addition to this, the thesis offers an introductory background and overview chapter revolving around repolarization lability. The results should be taken into account in further studies, so that the beat-to-beat variations of QT interval in ECG parameters and VCG descriptors can be utilized more effectively in clinical applications.
Open Access
Analysis, Modelling, Design, and Control of DC-DC Converter for Renewable Power Generation Systems
(2021) Parvez, Mohammad; Al-Sarawi, Said F.; Abbott, Derek; School of Electrical and Electronic Engineering
Global energy demand is rapidly growing and therefore meeting the future energy demand is becoming a major concern worldwide. To meet the energy demand, fossil fuels are still used as the primary energy source. However, these hydrocarbonbased fuels produce greenhouse gases that adversely affect environment and human health. Therefore, alternative renewable energy sources such as solar, wind, hydro, biomass and geothermal are getting very popular. Currently, development of power converters for these renewable energy sources is becoming more and more essential for converting this energy to appropriate voltage levels or feeding it to electrical power distribution networks. This research study is focused on the DC-DC boost converter analysis, design, modelling, and using current control techniques for singlephase uninterruptible power supply (UPS) inverter systems. The major contributions of the presented work can be categorized into two parts: Firstly, a comprehensive analysis of classical and advanced DC-DC converter topologies for renewable power applications. DC-DC power converters have attracted significant attention due to their increased use in a number of applications from aerospace to biomedical devices. The interest in wide bandgap (WBG) power semiconductor devices stems from outstanding features of WBG materials and power device operation at higher temperatures, larger breakdown voltages and sustaining larger switching transients than silicon (Si) devices. As a result, recent progress and development of WBG power devices based converter topologies are well-established for power conversion applications in which classical Si based power devices show limited performance. Currently, WBG devices such as silicon carbide (SiC) and gallium nitride (GaN) are the most promising semiconductor materials that are being considered for new generation of power devices because of their high voltage operation, high current switching capabilities, very low ON resistance, good thermal conductivity, etc. Secondly, a cost effective design of Gallium nitride (GaN)-based high-frequency, high efficiency DC-DC boost converter owing to preferred soft-switching features. The use of new power semiconductor devices such as GaN high electron mobility transistors (GaN HEMTs) are able to minimize switching losses, allowing high switching frequencies (from kHz to MHz) for realizing compact and fully integrated power converters. Finally, PI and PR control parameters are optimally tuned, and experimentally tested for single-phase UPS inverters to obtain very low total harmonic distortion (THD), zero steady-state error, and fast response. This research presents detailed analysis and mathematical models of PI and PR controllers in single-phase UPS inverter applications. In order to realize the importance of PR control features over conventional PI controllers, a PI controller is implemented in the same UPS inverter and mathematically analyzed. The performance of these controllers is analyzed in terms of steady-state is and transient responses and current harmonics level. The experimental result shows that the PR controller achieves zero steady-state error, improved transient response and reduced low-order harmonics distortion of the output current compared to PI controller. The performances of the implemented controllers are simulated and compared using the MATLAB/Simulink modeling environment. The main significance of this work is the design and development of a DC-DC boost converter, and optimization of controller parameters for high power application such as Electric Vehicle (EV) charging, aerospace, renewable power generation, etc.
Open Access
Aspects of HF communications: HF noise and signal features.
(2008) Giesbrecht, James E.; Abbott, Derek; Clarke, Russell; School of Electrical and Electronic Engineering
To many, high-frequency (HF) radio communications is obsolete in this age of long distance satellite communications and undersea optical fiber. Yet despite this, the HF band is used by defence agencies for backup communications and spectrum surveillance, and is monitored by spectrum management organizations to enforce licensing. Such activity usually requires systems capable of locating distant transmitters, separating valid signals from interference and noise, and recognizing signal modulation. Research presented here targets the latter issue. The ultimate aim is to develop robust algorithms for automatic modulation recognition of real HF signals, where real means signals propagating by multiple ionospheric modes with co-channel signals and non- Gaussian noise. However, many researchers adopt Gaussian noise models for signals for the sake of convenience at the cost of accuracy. Furthermore, literature describing the probability density function (PDF) of HF noise does not abound. So an additional aim of this research is measurement of the PDF of HF noise. A simple empirical technique, not found in the literature, is described that supports the hypothesis that HF noise is generally not Gaussian. In fact, the probability density function varies with the time of day, electromagnetic environment, and state of the ionosphere. Key contributions of this work relate to the statistics of HF noise and the discrimination of real HF signals via three signal features. Through two unique experiments, the density function of natural HF noise is found to closely follow a Bi-Kappa distribution. This distribution can model natural and man-made HF noise through a single control parameter. Regarding signal features, the coherence function is found to be a brute-force technique suitable only for hard (not soft) decisions. A novel application of an entropic distance measure proves able to separate four real HF signals based on their modulation types. And, an estimator for signal-to-noise (SNR) ratio is shown to provide reasonable measures of SNR for the same real HF signals.
Open Access
Aspects of quantum game theory
(2005) Flitney, Adrian P.; Abbott, Derek; School of Electrical and Electronic Engineering
Quantum game theory is an exciting new topic that combines the physical behaviour of information in quantum mechanical systems with game theory, the mathematical description of conflict and competition situations, to shed new light on the fields of quantum control and quantum information. This thesis presents quantizations of some classic game-theoretic problems, new results in existing quantization schemes for two player, two strategy non-zero sum games, and in quantum versions of Parrondo's games, where the combination of two losing games can result in a winning game. In addition, quantum cellular automata and quantum walks are discussed, with a history-dependent quantum walk being presented.
Open Access
Aspects of stochastic control and switching: from Parrondo’s games to electrical circuits.
(2009) Allison, Andrew Gordon; Abbott, Derek; Pearce, Charles Edward Miller; School of Electrical and Electronic Engineering
The first half of this thesis deals with the line of thought that leads to the development of discrete games of chance as models in statistical physics, with an emphasis on analysis of Parrondo’s games. The second half of the thesis is concerned with applying discrete games of chance to the modelling of other phenomena in the discipline of electrical engineering. The important features being the element of switching that is implicit in discrete games of chance and the element of uncertainty, introduced by the random aspect of discrete games of chance.
Open Access
Big data analysis of cyclic alternating pattern during sleep using deep learning
(2021) Hartmann, Simon; Baumert, Mathias; Abbott, Derek; School of Electrical and Electronic Engineering
Sleep scoring has been of great interest since the invention of the polysomnography method, which enabled the recording of physiological signals overnight. With the surge in wearable devices in recent years, the topic of what is high-quality sleep, how can it be determined and how can it be achieved attracted increasing interest. In the last two decades, cyclic alternating pattern (CAP) was introduced as a scoring alternative to traditional sleep staging. CAP is known as a synonym for sleep microstructure and describes sleep instability. Manual CAP scoring performed by sleep experts is a very exhausting and time-consuming task. Hence, an automatic method would facilitate the processing of sleep data and provide a valuable tool to enhance the understanding of the role of CAP. This thesis aims to expand the knowledge about CAP by developing a high-performance automated CAP scoring system that can reliably detect and classify CAP events in sleep recordings. The automated system is equipped with state-of-the-art signal processing methods and exploits the dynamic, temporal information in brain activity using deep learning. The automated scoring system is validated using large community-based cohort studies and comparing the output to verified values in the literature. Our findings present novel clinical results on the relationship between CAP and age, gender, subjective sleep quality, and sleep disorders demonstrating that automated CAP analysis of large population based studies can lead to new findings on CAP and its subcomponents. Next, we study the relationship between CAP and behavioural, cognitive, and quality-of-life measures and the effect of adenotonsillectomy on CAP in children with obstructive sleep apnoea as the link between CAP and cognitive functioning in children is largely unknown. Finally, we investigate cortical-cardiovascular interactions during CAP to gain novel insights into the causal relationships between cortical and cardiovascular activity that are underpinning the microstructure of sleep. In summary, the research outcomes in this thesis outline the importance of a fully automated end-to-end CAP scoring solution for future studies on sleep microstructure. Furthermore, we present novel critical information for a better understanding of CAP and obtain first evidence on physiological network dynamics between the central nervous system and the cardiovascular system during CAP.
Open Access
Broadband monolithic constrained lens design.
(2009) Hall, Leonard Thomas; Abbott, Derek; School of Electrical and Electronic Engineering
Constrained lens geometries have attracted attention as a replacement for bulky mechanical beam-steering systems or complex and expensive electronically beam scanned systems. Despite the great potential of constrained lenses, poor matching techniques and port implementation have limited the performance of Rotman lenses. This thesis provides a thorough engineering methodology for designing and analysing Rotman lenses. This has been achieved by reworking the Rotman equations for the intended application of a linear antenna array feed network. Further, a number of statistical methods are presented to evaluate the performance of the Rotman lens, providing a set of tools to optimise the lens for any linear array specification. While mathematical analysis of the Rotman lens using geometrical optics has occupied much of the work in the literature, the real challenges of constrained lens design have been only briefy reported. These challenges include the design of port geometries, feed networks, and impedance matching, which are particularly significant due to the desire to exploit the broadband potential of constrained lenses. The electromagnetic limitations of the Rotman lens architecture are presented with the analysis and fabrication of a 5 to 20 GHz Rotman lens design. In doing so, the mechanisms that limit lens performance are highlighted. This thesis presents a clear path through the minefield of design transforms to a Rotman lens that transforms its broadband potential to reality.
Open Access
Cardiac flow analysis using magnetic resonance imaging.
(2009) Wong, Kelvin Kian Loong; Mazumdar, Jagan Nath; Abbott, Derek; Kelso, Richard Malcolm; Worthley, Stephen Grant; Sanders, Prashanthan; School of Electrical and Electronic Engineering
Many types of cardiac abnormality have an implication on blood flow. However, most present-day diagnostic modalities analyse myocardial structures and not the cardiac flow within to detect heart defects in vivo. Currently, various imaging modalities, such as echocardiography, single photon emission computed tomography (SPECT), positron emission tomography (PET), X-ray computed tomography (CT), and cardiac magnetic resonance imaging (CMRI) provide a non-invasive approach for scanning humans with heart abnormalities, and are utilised in the management of cardiac patients. There is a need to develop a visualisation system for analysing flow of blood within the human heart. Motional properties of blood can be measured against normal controls and patients with cardiac abnormalities in order to discover underlying cause of these flow phenomena. This can potentially extend medical knowledge of the defects and their hemodynamic behaviour. We characterise motion patterns of blood in the human heart and analyse the flow properties, by means of tracking, using a series of time dependent magnetic resonance images. An indication of flow vortices can be provided by numerical computation of vorticity values within the defined region of blood flow. The global estimation of parametric motion flow fields over the whole image provides useful information on the presence of vortices within the heart chamber that can be used to assess cardiac functions. In this study, the crucial strategies for this approach are implemented, and the achievable diagnostic results and quality of assessment are investigated. The developmental stages of the framework and system design of each component for cardiac diagnosis are detailed in this thesis. The key objectives of the research and development for this diagnostic system are implemented herein: 1. Realisation of a non-invasive technique to compute flow features within cardiac structures. System evaluation and velocity calibration of the flow tracker are incorporated in the study. Verification of calculated flow in time-resolved cardiac vessels is performed by error analysis using flow fields constructed by velocityencoded magnetic resonance imaging velocimetry. 2. Measurement of cardiac vorticities in heart chambers is performed for investigation of flow phenomena. We examine the time-dependent behaviour of cardiac flow structures in the heart. The variation of flow patterns that are associated with myocardial wall deformations and pressure changes is analysed. 3. Realisation of a statistical framework for examining variations of flow due to myocardial defects in the heart. The quantification of flow will offer the potential to complement diagnostic methods that analyse cardiac defects and evaluate patient condition after surgical intervention. As an alternative to established medical imaging-based diagnostic techniques such as chest X-rays, and pulsed or continuous wave Doppler ultrasound scans for cardiac diagnosis, we develop a magnetic resonance imaging based approach and perform flow quantification to analyse the heart, vis-`a-vis blood movement in chambers based on a measured flow field. This framework offers potential for non-invasive flow visualisation in cardiac structures. We validate this methodology specifically for analysing flow characteristics within a human heart case study. We also demonstrate the potential for non-invasive assessment of cardiac abnormality for a pathological case of the heart.
Open Access
Characterizing and mitigating scattering effects in terahertz time domain spectroscopy measurements.
(2013) Kaushik, Mayank; Ng, Brian Wai-Him; Fischer, Bernd Michael; Abbott, Derek; School of Electrical and Electronic Engineering
Terahertz research has came a long way since its inception in the mid 1980s when the first pulsed THz emission was reported using electro-optic sampling. With rapid advent in THz generation and detection techniques, research in terahertz time-domain spectroscopy (THz-TDS) has progressed to such a great extent that terahertz is finding potential use in real world applications such as biomedical sensing, security screening and defence related applications. While many researchers and commercial organizations have successfully demonstrated efficacy of terahertz, various challenges still exist before THz technology transitions from the realm of research into everyday life. This thesis focuses on the topical area of characterization and mitigation of scattering in terahertz time-domain spectroscopy measurements. Motivated by the lack of theoretical models and signal processing techniques, this thesis, presents several pieces of novel work that include theoretical models, numerical methods, signal processing techniques and experimental procedures to estimate and mitigate the scattering contribution in THz-TDS measurements of dielectric materials. The thesis is divided in to three main sections: Section I describes the various theoretical models developed for estimating and approximating the scattering cross-section, when an electromagnetic wave interacts with a random medium with characteristic particle dimensions comparable to the wavelength of the incident radiation. The section is divided in two main sub-sections, (i) scattering through a sparse distribution of particles, and (ii) scattering from dense media. Section II presents several signal processing based approaches for estimating and mitigating scattering effects in THz-TDS measurements for samples that exhibit sharp and sparse absorption features, without requiring a priori information such as its granularity, refractive index, and density. Section III discusses some common experimental techniques such as milling the material of interest into fine powder and time domain averaging spatially disjoint or multiple sample measurements, in order to reduce the presence of scattering features and effects in the THz-TDSmeasurements. Recognizing the invasive access and/or specializedmeasurement apparatus requirement for these techniques, we present our preliminary investigation in analysing multiple Fresnel echoes for estimating and mitigating scattering contribution in THz-TDS measurements. In addition to this, the thesis offers an introductory background to THz-TDS, in areas of hardware, applications, signal processing, and terahertz interaction with matter.
Open Access
A complex systems approach to important biological problems.
(2007) Berryman, Matthew John; Abbott, Derek; Allison, Andrew Gordon; School of Electrical and Electronic Engineering
Complex systems are those which exhibit one or more of the following inter-related behaviours: 1. Nonlinear behaviour: the component parts do not act in linear ways, that is the superposition of the actions of the parts is not the output of the system. 2. Emergent behaviour: the output of the system may be inexpressible in terms of the rules or equations of the component parts. 3. Self-organisation: order appears from the chaotic interactions of individuals and the rules they obey. 4. Layers of description: in which a rule may apply at some higher levels of description but not at lower layers. 5. Adaptation: in which the environment becomes encoded in the rules governing the structure and/or behaviour of the parts (in this case strictly agents) that undergo selection in which those that are by some measure better become more numerous than those that are not as “fit”. A single cell is a complex system: we cannot explain all of its behaviour as simply the sum of its parts. Similarly, DNA structures, social networks, cancers, the brain, and living beings are intricate complex systems. This thesis tackles all of these topics from a complex systems approach. I have skirted some of the philosophical issues of complex systems and mainly focussed on appropriate tools to analyse these systems, addressing important questions such as: • What is the best way to extract information from DNA? • How can we model and analyse mutations in DNA? • Can we determine the likely spread of both viruses and ideas in social networks? • How can we model the growth of cancer? • How can we model and analyse interactions between genes in such living systems as the fruit fly, cancers, and humans? • Can complex systems techniques give us some insight into the human brain?
Open Access
Design and Analysis of Advanced Photonic Devices for Electromagnetic Transmission and Sensing
(2021) Islam, Saiful; Abbott, Derek; Ng, Brian W.-H.; School of Electrical and Electronic Engineering
In this thesis, we report the investigation of advanced photonic devices for electromagnetic transmission and biochemical sensing in the terahertz and optical regimes. The choice of material for designing a terahertz device is deemed to be one of the most crucial factors. First, we consider materials that are frequently used in making terahertz devices. We experimentally demonstrate the optical, thermal, and chemical properties of various chosen glasses, polymers, and resin to select the optimal material for terahertz. Second, we perform a broad review on terahertz optical fibres—this includes various fibre categories, their guiding mechanisms, fabrication methodologies, possible experimental methodologies, and applications. Third, we analyse and demonstrate the design of various fibre structures for terahertz transmission and sensing, and then perform experiments on a hollow core antiresonant fibre. We demonstrate successful fabrication of an asymmetrical Zeonex fibre using a novel fabrication method. This is carried out by using a tabletop horizontal extruder designed for producing polymer filaments. The fabricated fibre is then experimentally investigated for terahertz transmission and gas sensing. Fourth, we study optical fibre based surface plasmon resonance biosensors for operation in the optical regime. Theoretical studies are undertaken to obtain the best possible sensor in consideration of performance, experimental feasibility, and fabrication. One of the optimized sensors is then fabricated as a possible candidate for possible realworld sensing applications. Finally, we study metasurface planar devices for achieving high sensitivity and quality factor in the terahertz regime. We first demonstrate a tunable graphene metasurface that can achieve multi-band absorption and high refractometric sensing. Later, we demonstrate on an all-dielectric metasurface that reports highest Q-factor in the terahertz regime. We fabricate and experiment on the dielectric metasurface and find good agreement with the simulation.
Open Access
Design techniques for low power mixed analog-digital circuits with application to smart wireless systems.
(2003) Al-Sarawi, Said Fares Khalil; Abbott, Derek; School of Electrical and Electronic Engineering
This dissertation presents and discusses new design techniques for mixed analog-digital circuits with emphases on low power and small area for standard low-cost CMOS VLSI technology. The application domain of the devised techniques is radio frequency identification (RFID) systems, however the presented techniques are applicable to wide range of mixed mode analog-digital applications. Hence the techniques herein apply to a range of smart wireless or mobile systems. The integration of both analog and digital circuits on a single substrate has many benefits such as reducing the system power, increasing the system reliability, reducing the system size and providing high inter-system communications speed - hence, a cost effective system implementation with increased performance. On the other hand, some difficulties arise from the fact that standard low-cost CMOS technologies are tuned toward maximising digital circuit performance and increasing transistor density per unit area. Usually these technologies have a wide spread in transistor parameters that require new design techniques that provide circuit characteristics based on relative transistor parameters rather than on the absolute value of these parameters. This research has identified new design techniques for mostly analog and some digital circuits for implementation in standard CMOS technologies with design parameters dependent on the relative values of process parameters, resulting in technology independent circuit design techniques. The techniques presented and discussed in this dissertation are (i) applied to the design of low-voltage and low-power controlled gain amplifiers, (ii) digital trimming techniques for operational amplifiers, (iii) low-power and low-voltage Schmitt trigger circuits, (iv) very low frequency to medium frequency low power oscillators, (v) low power Gray code counters, (vi) analog circuits utilising the neuron MOS transistor, (vii) high value floating resistors, and (viii) low power application specific integrated circuits (ASICs) that are particularly needed in radio frequency identification systems. The new techniques are analysed, simulated and verified experimentally via five chips fabricated through the MOSIS service.
Open Access
Design, characterisation and optimisation of a SAW correlator driven, wireless, passive microvalve for biomedical applications.
(2010) Tikka, Ajay Chandra; Al-Sarawi, Said Fares Khalil; Abbott, Derek; School of Electrical and Electronic Engineering
The culmination of rapid advances made in the areas of microelectromechanical systems (MEMS), nonregenerative power sources, nanotechnology, and biomedical engineering have resulted in the expansion of their horizons in modern medicine for the deployment of a wide array of implantable devices. However, the lifetime and remote interrogability of implants, specifically used for drug delivery applications, has been an issue of contention, as their deployment period is limited by the battery life and the device size. Furthermore, not much research effort is directed towards remotely controlled flow manipulation using passive components. These shortcomings are addressed in this thesis by employing surface acoustic wave (SAW) technology to design a novel RF powered, secure coded, active microvalve with fully passive components. By combining the complex signal processing capabilities of the acoustic wave correlator with the electrostatic actuation of the microchannel, the advantages of both the mechanisms are incorporated into a novel microvalve design. Fluid pumping can be achieved at ultrasonic frequencies by electrostatically actuating the edge clamped microchannel, placed in between the compressor interdigital transducer’s (IDT’s) of two identical SAW correlators. The ability to wirelessly administer doses of drug accurately, for an extended period of time, at an inaccessible target location, through an implanted microvalve has the potential to revolutionise health care for long-term, controlled drug release applications. Three specific and diverse areas within MEMS, the new device builds on, are investigated by taking a comprehensive design, modelling, optimisation and experimental validation approach for majority of the research endeavors in the thesis. The first area corresponds to SAW technology followed by microfluidics, and body-centric communications; driven by the ultimate goal to demonstrate the operational feasibility of a human implanted, wirelessly controlled microvalve. The proposed specialised design necessitated a thorough understanding of the multiple coupled physics phenomena at the process level, before fabrication, for the critical investigation and refinement of the individual microvalve components. A comprehensive finite element modelling technique, where the complete set of partial differential equations are solved, was used to design these microvalve components with low level of abstraction to enable an automatic inclusion of the majority of the second order effects. As a starting point for the FEM modelling of SAW devices, an infinite periodic grating was modelled to analyse the freely propagating eigenmodes and eigenvalues with modal analysis; and electrically active waves and electrical admittance with harmonic analysis. A curve fitting technique was employed to extract the COM/P-matrix model parameters from these FEM results. Furthermore, an experimental validation of the parameters extracted using this novel combination of FEM and fitting techniques was carried out by fabricating a number of delaylines and comparing the physical structure response with the formulated P-matrix model. On the other hand, the modelling of a 2 and 3-dimensional, 5×2-bit Barker sequence encoded acoustic wave correlator was demonstrated using FEM. The correlator’s response was quantified in terms of harmonic analysis, to obtain the electrical admittance and output voltage profile, and transient analysis, to study the acoustic wave propagating characteristics and correlation pulses. The validation of these simulation results was carried out by fabricating the SAW correlators using optical lithographic techniques. A good agreement between the numerical and experimental results highlighted the feasibility and potential of using FEM for application specific modelling of SAW correlators. The complexity involved in combining the electroacoustic correlation and electrostatic actuation mechanisms, necessitated a systematic design and optimization of the novel microvalve which is best possible with FEM. In this thesis, the emphasiswas on the design and optimisation of a novel microfluidic structure through the deflection analysis, both, to verify the functionality of the concept and to investigate the working range of the structure. Secure interrogability of the microvalve was demonstrated by utilising finite element modelling of the complete structure and the quantitative deduction of the code dependent, harmonic and dynamic transient microchannel actuation. A numerical and experimental analysis of the biotelemetry link for the microvalve was undertaken in the vicinity of numerical and physical human body phantoms, respectively. To accurately account for the path losses and to address the design optimisation, the receiver coil/antenna was solved simultaneouslywith the transmitter coil/antenna in the presence of a human body simulant using 3-dimensional, high frequency electromagnetic, FEM modelling. The received relative signal strength was numerically and experimentally derived for a miniature (6×6×0.5 mm), square spiral antenna/coil when interrogated by a hand-held 8×5×0.2 cm square spiral antenna/coil in the near field. Finally, the experimental results confirmed well with the FEM analysis predictions and hence ascertained the applicability of the developed system for secure interrogation and remote powering of the newly proposed microvalve.
Open Access
Detection of cardiorespiratory interaction for clinical research applications.
(2012) Kabir, Muammar Muhammad; Baumert, Mathias; Abbott, Derek; School of Electrical and Electronic Engineering
Human physiological systems are a widely studied topic in the field of Biomedical Engineering. There is a particular interest in the study of human cardiovascular and respiratory systems since these two systems do not act independently; there exists a strong coupling between them. Experimental studies use the concept of synchronization to demonstrate the interaction between different physiological systems. Synchronization is the appearance of some relationship between two periodic oscillators in the form of locking of their phases or adjustment of rhythms. Cardiorespiratory coordination is an aspect of the interaction between heart and respiratory rhythm that has been reported not only at rest or during exercise, but also in subjects under the influence of anesthesia and drugs. Through the quantification of cardiorespiratory coordination we can achieve a better understanding of its physiological functioning. Some of the conventional signal-processing techniques such as power spectral density and cross-correlation analysis have shown linear dependencies between heart and respiratory rate. However, as these biological signals are inherently non-linear, nonstationary, and contain superimposed noise, the techniques mentioned above often prove to be inadequate for characterizing their complex dynamics. Therefore, to overcome these issues, it is required to develop a technique that is less sensitive to noise, robust and possibly provides additional information about the interaction between cardiac rhythms and respiration. This Thesis introduces a new and relatively simple approach for the quantification of cardiorespiratory interaction based on joint symbolic dynamics, which provides an easy interpretation of physiological data by a simplified description of the system’s dynamics. Furthermore, this Thesis investigates the association between cardiorespiratory coordination and some of the physiological mechanisms, and assesses cardiorespiratory coordination as a marker of cardiorespiratory system disturbances.
Open Access
Developments in double-modulated terahertz differential time-domain spectroscopy.
(2010) Balakrishnan, Jegathisvaran; Abbott, Derek; Fischer, Bernd Michael; Mickan, Samuel Peter; School of Electrical and Electronic Engineering
Recent years have seen a plethora of significant advances in terahertz (THz or T-ray) technology with the rapid development of the ultrafast femtosecond laser system. By definition, THz refers to an electromagnetic wave located between the microwave and infrared regions of the electromagnetic spectrum. Over the last two decades, there has been an enormous interest in improving the sensitivity of spectroscopicmeasurements on liquids in the terahertz regime. Liquid studies at terahertz frequencies (0.1 - 10 THz) allow analysis of chemical composition and provides a better understanding of the solvation dynamics of various types of liquids. This Thesis focusses on developing a novel spinning wheel device using a doublemodulated terahertz differential time-domain spectroscopy (double modulated THz-DTDS) scheme coupled with a simultaneous dual-waveform acquisition technique for increasing the sensitivity and repeatability of liquid studies. The spinning wheel device promises a rapid succession of measurements, requiring one mechanical delay scan for the sample and reference signals. The double-modulated THz-DTDS scheme with simultaneous dual-waveform acquisition was first introduced by Mickan et al. (2004). This Thesis builds upon this former work with a modification in the signal extraction technique. In this work, a step-bystep systematic engineering approach has been employed for the development of the spinning wheel device. The Thesis is categorised into several parts leading to the development of the spinning wheel device. The first part provides a review on the historical development of the electromagnetic spectrum and a review of the state-of-the-art regarding THz generation and detection based on transient photoconductivity. Identifying an optimal polymer window material forms the second part of this Thesis. Here, a range of polymer materials are tested for low hygroscopicity and high transmission coefficient. The third part of the Thesis reviews various window cell geometries used in liquid spectroscopy measurements. A detailed data analysis technique is described for each geometry. The fourth part of the Thesis presents a prototype of the novel spinning wheel mechanism for THz material parameter extraction using the double-modulated THz-DTDS scheme. A proof-of-principle showing that the amplitude noise of a THz system decreases as a function of the spinning wheel modulation frequency is demonstrated. Preliminary experiments indicate the potential of this technique for achieving a better noise performance, which is of significance particularly for THz spectroscopy of polar liquids where the signal-to-noise ratios are typically low due to high absorption coefficient. The initial demonstration of the spinning wheel technique leads to THz spectroscopy of liquids based on a fixed dual-thickness window geometry. Here, a rapid switching between two fixed liquid sample thicknesses is introduced.
Open Access
Dielectric resonator antennas : from multifunction microwave devices to optical nano-antennas.
(2013) Zou, Longfang; Fumeaux, Christophe; Withayachumnankul, Withawat; Abbott, Derek; School of Electrical and Electronic Engineering
Since a cylindrical dielectric resonator antenna (DRA) was firstly proposed by Long et al. in the 1980s, extensive research has been carried out on analyzing DRA shapes, characterizing the resonant modes, improving their radiation characteristics with various excitation schemes. Compared with conventional conductor-based antennas, DRAs have attractive features such as small size, high radiation efficiency and versatility in their shape and feeding mechanism. Importantly, various orthogonal modes with diverse radiation characteristics can be excited within a single DRA element. These modes can be utilized for various requirements, which makes the DRA a suitable potential candidate for multifunction applications. Based on this principle, this thesis presents different multifunction designs: Firstly a cross-shaped DRA with separately fed broadside circularly polarized (CP) and omnidirectional linearly polarized (LP) radiation patterns and, secondly, a multifunction annular cylindrical DRA realizing simultaneously omnidirectional horizontally and vertically polarized radiation patterns with low cross-coupling. The evolution, design process and experimental validation of these two antennas are described in details in the thesis. The second part of the thesis dramatically scales down DRA to shorter wavelengths. Inspired by the fact that DRA still exhibits high radiation efficiency (>90%) in the millimetre wave range, while the efficiency of conventional metallic antenna degrades rapidly with frequencies, this thesis proposes the concept of nanometer-scale DRA operated in their fundamental mode as optical antennas. To validate the concept, optical DRA reflectarrays have been designed and fabricated. Although the zeroth-order spatial harmonic reflection is observed in the measurement due to the imperfect nanofabrication, the power ratio of deflected beam to the specular component of reflection amounts to 4.42, demonstrating the expected operation of the reflectarray. The results strongly support the concept of optical DRA and proposes design methods and strategies for their realization. This proof of concept is an essential step for future research on nano-DRA as building block of emerging nano-structured optical components.
Open Access
Distributed home agent mobility management for IP based cellular network.
(2013) Yung, Chi Wah; Coutts, Reginald Paul; Abbott, Derek; School of Electrical and Electronic Engineering
The convergence of wireless networks both fixed and mobile with the Internet is creating a revolution in the way wireless networked resources interact with each other. This thesis is concerned with mobile networks and proposes to deal with the mobility management problems for the mobile computing devices in the next generation of multi-technologies integrated IP based mobile networks. In order to do this, a new distributed home agent approach for mobility management has been developed that harmonizes the concept of micro-mobility and macro-mobility management in order to enable seamless mobility management on different kinds of wireless network environment especially interaction with the legacy cellular network in which resources are limited and expensive. The major contribution of this thesis is three-fold. Firstly, this thesis proposes network access architecture and a distributed mobility management scheme, which enables the mobility of a mobile device in a cellular packet data network in order to reduce the latency and network traffic required to handle the mobility management functionality. A detailed design of the distributed mobility management scheme is presented for the implementation and the conceptual model is analysed. Secondly, simulation of the mobility management schemes using two different network simulation packages to enable a comparison of the simulator functionalities is presented. Finally, the results of the simulation and suggested future work are presented.
Open Access
Efficient terahertz-range beam control using flat optics
(2017) Headland, Daniel; Abbott, Derek; Withayachumnankul, Withawat; Webb, Michael; School of Electrical and Electronic Engineering
The terahertz range, which spans 0.1 to 10 THz of the electromagnetic spectrum, has significant potential for numerous diverse uses including high-volume short-range communications, non-invasive and non-destructive sub-dermal medical imaging, and safe imaging of personnel and postal items for security applications. These capabilities are identified due to the unique properties of terahertz radiation; terahertz waves are of high carrier frequency relative to conventional wireless communications, are able to transmit through dry, non-polar substances, and yet are non-ionising. However, owing to factors including a lack of available power and significant atmospheric attenuation, it is challenging to maintain sufficient signal power over a realistic propagation distance for terahertz waves. For this reason, the terahertz range is presently lacking in practical applications, and hence it occupies an under-utilised portion of the electromagnetic spectrum. As unused spectrum is a valuable resource, the development of technologies to exploit the terahertz range is a highly desirable goal. Beam-control techniques—the capacity to shape and steer electromagnetic radiation— can prevent radiated power from being lost to undesired directions. Thus, techniques of this variety have the capacity to address the aforementioned obstacles to the realisation of practical terahertz technologies. This thesis is therefore centred around the development of terahertz beam-control devices that satisfy two criteria. Firstly, the beam manipulation operation must be highly efficient, as much of the motivation of this work is to mitigate the constraints upon power. Secondly, planar devices are preferable, as this is a requirement for compact systems. With these restrictions in mind, various techniques are explored for their viability in future applications of terahertz technology, including various forms of metallic and dielectric resonators, 3D printing, and composite materials with effective properties. The advantages and drawbacks of each approach are evaluated.
Open Access
Electroencephalographic analysis of overnight sleep recordings in children with sleep-disordered breathing
(2024) Ebrahimpour, Maryam; Baumert, Mathias; Abbott, Derek; School of Electrical and Mechanical Engineering
The electroencephalogram (EEG) stands out as a valuable non-invasive tool for monitoring brain activities. However, EEG signals are prone to artefacts, including those originating from cardiac activity, which complicates accurate data interpretation. This research explores techniques specifically designed to eliminate cardiac artefacts from EEG signals, essential for enhancing the accuracy of biomedical signal processing. Two methods of cardiac artefact removal are developed and investigated in this thesis. The first method involves rejecting excessively contaminated segments and can be applied online and in real-time to single-channel EEG when an ECG signal is available. The second study entails evaluating four common ICA methods to specifically extract cardiac artefact component from 16-channel EEG. The investigation concludes that second order blind identification (SOBI) is the most effective algorithm for this specific application. Moreover, this thesis probes EEG potential as a biomarker, focusing particularly on heartbeat-evoked potentials (HEP) and frontal asymmetry. In relation to HEP, which is a crucial measure of the connectivity between the heart and the brain, our findings indicate that HEP is most prominent in fronto-central areas and the frontal lobe, supporting the hypothesis that considers the insula and somatosensory cortex as the source of HEP in the brain. Additionally, HEP reaches its maximum value during the REM stage of sleep, suggesting that the heightened vigilance during REM sleep may affect HEP strength. However, as a biomarker for recovery from sleep apnea and its related symptoms, we find that HEP does not effectively differentiate between surgery and control group. Another study performed in this thesis focuses on frontal asymmetry as a biomarker for depression in children using sleep EEG. Our findings do not demonstrate a significant relationship between frontal asymmetry and depression. Collectively, this thesis contributes to the advancement of EEG signal processing, artefact removal methodologies, and the utilization of physiological markers in clinical research.
Open Access
Engineering aspects of terahertz time-domain spectroscopy.
(2010) Withayachumnankul, Withawat; Abbott, Derek; Fischer, Bernd Michael; Mickan, Samuel Peter; School of Electrical and Electronic Engineering
Terahertz time-domain spectroscopy (THz-TDS) is a technique capable of measuring optical constants ofmaterialswith T-ray frequencies, bounded between 0.1 and 10 THz. Owing to the infancy of the technology, much work has to be carried out to improve its utility and reliability. Engineering aspects become vital to support its operation that relies on physical phenomena. This thesis, in the arena of engineering, encompasses a variety of original THz-TDS projects, which aim for (Part I) signal enhancement and classification, (Part II) system evaluation and optimisation, and (Part III) T-ray optics: Part I is relevant to enhancement and classification of T-ray signals via digital signal processing. In one project, information underlying T-ray signals is enhanced through numerical removal of unwanted artefacts that are introduced by the response of water vapour during the measurement. In another project, machine learning is recruited in classification of visually indistinguishable T-ray signals probing materials of the same general class. Part II focuses on THz-TDS systems with a particular interest in the measurement precision. An ISO standard for the evaluation of measurement uncertainty is adopted for assessing the uncertainty in THz-TDS measurements. The result is an analytical uncertainty model, which allows an improvement in the measurement precision through optimisation of a model parameter in the subsequent work. Part III involves design, fabrication, and characterisation of THz-TDS hardware components, i.e., antireflection windows and multilayer interference filters. The designs are based upon conventional optical interference theory. Despite that, required materials and fabrication processes are completely different from those used in optics due to the distinctive operating wavelengths, which dictate material responses and structural dimensions. In addition to these parts of the original contributions, the thesis offers an introductory background to THz-TDS, in the areas of hardware, applications, and data processing.

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