Electrical and Electronic Engineering - Doctoral Theses

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    Development of a bio-impedance measurement system for bladder monitoring
    (University College Cork, 2022-11-01) Behrouzirad, Ardeshir; Galvin, Paul; McCarthy, Kevin G.; Sugrue, Patrick; Science Foundation Ireland; Electronic Components and Systems for European Leadership
    The occurrence of disturbance in the control of urine flow and voiding, which leads to involuntary leakage, is called Urinary Incontinence (UI), and it may happen due to several factors such as pregnancy, family background, neurological disorders, etc. It has a negative impact on the social life and also the physical health of patients, highlighting the need for a mechanism to monitor the patient’s bladder and warn them during their routine daily activities. For this purpose, the development of a low cost bio-impedance measurement system as a method for bladder monitoring is investigated in this thesis. Prior to this thesis, the trend in the literature was to identify the correlation between the change of the impedance and the accumulation of urine in the bladder. Categorizing the current challenges and designing a bioimpedance measurement system, this thesis employs a vertical monitoring method, as a feasibility study, to increase the sensitivity of the measurement of impedance variation related to bladder fullness. Also, it employs a separate mechanism with extra sets of electrodes to address the issue of bladder relocation and its impact on the monitoring. The findings of the vertical monitoring method, with around 400 experiments performed on a phantom mimicking the abdomen and bladder, indicated the increased sensitivity of 45% and 52% in the measured impedance for two different urine conductivities, 1 and 2 S/m, respectively, after reaching 60 ml of volume, compared to the conventional horizontal monitoring in bio-impedance measurement. For the extra monitoring mechanism, when the target was relocated, with more than 500 experiments on the phantom, the sensitivity was increased between 1.43 to 4.61 times compared to the conventional horizontal method, depending on the urine conductivity and location of the target. The location of the target was found to be a key factor as the distance of the target to the electrodes recording the impedance change can vary and lead to erroneous outcomes, especially in the case where the bladder is far from the electrodes, due to individual parameters such as the weight or even posture. In summary, the thesis made an impact towards a non-invasive, wearable bio-impedance measurement system for bladder monitoring, by identifying and addressing important issues related to the areas that are still at their early stages.
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    Thin film magnetics for integrated magnetic nano-structures
    (University College Cork, 2022-11-01) Cronin, Darragh; McCloskey, Paul; O Mathuna, Cian; Masood, Ansar; Science Foundation Ireland
    The past decades have seen a surge in demand for highly miniaturised magnetic components which has been enabled by use of power circuitry high switching frequencies which require energy storage on a smaller scale. The optimal scale of this integration will be achieved with the complete integration of the power supply onto silicon. Hence there is a demand for soft magnetic materials for power conversion applications in the high MHz frequency range. These materials should exhibit crucial properties such as a low coercivity, high saturation magnetisation and a high resistivity for optimum performance. Methods to further optimise the intrinsic qualities of an ultra-soft magnetic material, CoZrTaB (CZTB) are presented. This includes methods to maintain in-plane, uniaxial magnetic anisotropy as well as efforts to produce composite soft magnetic materials such as CoZrTaB-N\textsubscript{2} via methods such as reactive sputtering. Furthermore Spin-Reorientation Transition in amorphous CZTB magnetic multilayers is investigated. This interesting phenomenon results from from a tuneable value of residual stress arising from a thermal shock effect at elevated temperatures, shifting the magnetic anisotropy from in-plane to out-of-plane. This study highlighted how external parameters such as stress and thermal effects can damage properties such as uniaxial magnetic anisotropy, essential for specific applications. Work on a novel soft magnetic composite – CoZrTaB-SiO\textsubscript{2} is also presented. This study involved the technique of co-sputtering to produce a composite amorphous magnetic and non-magnetic microstructure, comprehensively examining all aspects of the material and its vital properties resulting in an ultra-soft magnetic material. Moreover, this material exhibited an increased and tuneable resistivity, dependant on sputtering conditions. Finally, a detailed and systematic experiment to develop a low footprint inductor consisting of a 3-D vertical array of vertical copper cylinders (or pillars) coated in CZTB multilayers. This novel structure was designed for a low-footprint with high inductance-density values. This work focused precisely on the magnetic laminations and the techniques used to ensure vital properties were retained such as a low coercivity and a circumferential magnetic hard axis to correspond with the current induced magnetic field.
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    Design of clock and data recovery circuits for energy-efficient short-reach optical transceivers
    (University College Cork, 2022-12-19) Khanghah, Meysam M.; Townsend, Paul; Peters, Frank H.; Ossieur, Peter; Science Foundation Ireland
    Nowadays, the increasing demand for cloud based computing and social media services mandates higher throughput (at least 56 Gb/s per data lane with 400 Gb/s total capacity 1) for short reach optical links (with the reach typically less than 2 km) inside data centres. The immediate consequences are the huge and power hungry data centers. To address these issues the intra-data-center connectivity by means of optical links needs continuous upgrading. In recent years, the trend in the industry has shifted toward the use of more complex modulation formats like PAM4 due to its spectral efficiency over the traditional NRZ. Another advantage is the reduced number of channels count which is more cost-effective considering the required area and the I/O density. However employing PAM4 results in more complex transceivers circuitry due to the presence of multilevel transitions and reduced noise budget. In addition, providing higher speed while accommodating the stringent requirements of higher density and energy efficiency (< 5 pJ/bit), makes the design of the optical links more challenging and requires innovative design techniques both at the system and circuit level. This work presents the design of a Clock and Data Recovery Circuit (CDR) as one of the key building blocks for the transceiver modules used in such fibreoptic links. Capable of working with PAM4 signalling format, the new proposed CDR architecture targets data rates of 50−56 Gb/s while achieving the required energy efficiency (< 5 pJ/bit). At the system level, the design proposes a new PAM4 PD which provides a better trade-off in terms of bandwidth and systematic jitter generation in the CDR. By using a digital loop controller (DLC), the CDR gains considerable area reduction with flexibility to adjust the loop dynamics. At the circuit level it focuses on applying different circuit techniques to mitigate the circuit imperfections. It presents a wideband analog front end (AFE), suitable for a 56 Gb/s, 28-Gbaud PAM-4 signal, by using an 8x interleaved, master/ slave based sample and hold circuit. In addition, the AFE is equipped with a calibration scheme which corrects the errors associated with the sampling channels’ offset voltage and gain mismatches. The presented digital to phase converter (DPC) features a modified phase interpolator (PI), a new quadrature phase corrector (QPC) and multi-phase output with de-skewing capabilities.The DPC (as a standalone block) and the CDR (as the main focus of this work) were fabricated in 65-nm CMOS technology. Based on the measurements, the DPC achieves DNL/INL of 0.7/6 LSB respectively while consuming 40.5 mW power from 1.05 V supply. Although the CDR was not fully operational with the PAM4 input, the results from 25-Gbaud PAM2 (NRZ) test setup were used to estimate the performance. Under this scenario, the 1-UI JTOL bandwidth was measured to be 2 MHz with BER threshold of 10−4. The chip consumes 236 mW of power while operating on 1 − 1.2 V supply range achieving an energyefficiency of 4.27 pJ/bit.
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    AI-assisted analysis of heart sounds and interpretation of acoustic representation of brainwaves in neonates
    (University College Cork, 2022-08-18) Gomez Quintana, Sergi; Popovici, Emanuel; Temko, Andriy; Wellcome Trust; Grand Challenges Canada; Science Foundation Ireland
    Numerous reports from World Health Organisation (WHO) consistently list the diseases of the heart and the brain among the top three causes of death across the globe. In low and low-to-middle-income countries, the neonatal stage is the most dangerous of the whole life and is a time of particular concern for medical professionals and parents. Timely detection of abnormalities during the first days of life allows medical staff to make informed decisions which have life-saving consequences. For this, continuous monitoring is required and it has several challenges in a clinical setting. First, acquiring physiological data from neonates is not trivial, often involving time-consuming processes that require specialised training. Second, specific monitoring equipment is often expensive and not affordable in low-income communities. More importantly, the complexity of the data may be difficult to interpret even for trained professionals and the required expertise might not be available 24/7. Alternative methods and tools that are low cost and require minimum training while providing the accuracy level of a specialist medical professional are required. This work deals with the development of such methods for the analysis of neonatal heart and brain signals by means of artificial intelligence (AI) and AI-guided sonification. Sound analysis can play an important role as a non-invasive, intuitive, and cost-effective tool to facilitate the interpretation of physiological signals. Heart auscultation is already part of the clinical examination routine. It uses a stethoscope, which is a low cost and reliable tool to screen for neonatal heart defects. However, heart sound interpretation is subjective, dependent on the assessor’s hearing acuity and the acquired level of expertise. Assistance from AI can provide an objective interpretation of heart sounds to complement the traditional auscultation method. A novel, accurate method for detecting congenital heart disease in phonocardiogram (PCG) signals using AI is presented. When dealing with the brain abnormalities in newborns, neonatal seizures are one of the most common neurological conditions, and they need to be treated as a medical emergency with prompt detection and intervention. Electroencephalography (EEG), the gold standard for monitoring electrical brain activity, is often difficult to interpret visually and requires a highly specialised medical professional. These professionals might not be readily available in low or medium-income settings, and even in high-income countries, they might be available only in tertiary care centres and not present 24/7. AI-driven sonification of EEG for detection of neonatal seizures, which is developed in this work, helps to improve the detection of these threatening seizure events by decreasing the level of expertise required from healthcare professionals while maintaining the same accuracy. It is shown that AI-assisted sonification can augment the medical professional to make decisions which are better than AI alone while improving the interpretability of the made decisions, which is a key requirement in the medical domain. The proposed algorithms and methodologies are validated on numerous datasets. The developed prototypes are implemented using cloud and Internet of Things technologies. It is shown that these technologies allow for an affordable, real-time analysis of heart and brain physiological signals with minimum training.
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    Investigation of the high-frequency effects in Mn-Zn ferrites for EMI filter applications
    (University College Cork, 2022-08-22) Kącki, Marcin; Hayes, John G.; Ryłko, Marek S.; Sullivan, Charles R.; SMA Magnetics sp. z o.o.
    This thesis focuses on the analysis, identification, and experimental investigation of the high-frequency effects encountered within the magnetic core when used in high-frequency, high-power electromagnetic interference (EMI) filters. These applications require cost-optimized, high-performance, and high-power-density magnetic components. As the manufacturers’ material specifications usually do not provide sufficient information to optimize the design, this thesis develops new methods to determine the high-frequency properties of Mn-Zn ferrites up to 20 MHz. Complex permeability and permittivity, as well as specific power loss, are typically provided as one value by the manufacturer, regardless of the core shape and size. Therefore, various magnetic materials are characterized for their complex permeability and permittivity. These two parameters are of differentiated physical origins, and so two independent measurement fixtures are developed and built. The impacts of physical size, temperature and force on complex permeability and permittivity are also considered. The detailed analysis of magnetic flux is introduced based on a 1-D analytical model, a novel shell-based transmission-line model, and finally, based on the FEM and Maxwell 3D eddy-current field solver. These models are used to calculate the complex permeability characteristics for various core sizes made of two materials: 3E10 and 3F36. A complete experimental validation is presented for the calculated values. The analytical methods show a very good correlation with the experimental measurements. The novel shell-based transmission-line model has the best accuracy, and the calculation can be implemented into simulation of a higher-order system or into any other magnetic component design algorithm. Flux verification methods are developed which use precisely-bored cores to accurately predict flux distribution. The results of the flux propagation, starting from the simple three-hole model up to the advanced four-section model confirm that the magnetic flux distribution is affected by frequency-dependent dynamic effects. Flux distributions was experimentally measured for T50 and T80 cores made of 3E10 and 3F36 material. Results are consistent with the FEM simulations and help in the development of a more accurate analytical model. A novel laminated-core common mode choke (CMC) is developed and presented in this thesis. The presented CMC core structure divides the conduction path into sub-regions which allowing for the reduction of the high-frequency effects. Laminated cores, made of several Mn-Zn ferrite materials, were tested and special attention is paid to the effect of magnetic material selection, core size and lamination thickness on the core high-frequency performance. Common mode insertion loss characteristic for the novel CMC shows that laminated ferrite structure give rise to significant attenuation improvement.