Electrical and Electronic Engineering - Doctoral Theses
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- ItemDevelopment of electromagnetic vibration energy harvesters as powering solution for IoT based applications(University College Cork, 2022-09-20) Paul, Kankana; Roy, Saibal; Amann, Andreas; Kennedy, Peter; Science Foundation Ireland; Horizon 2020The drive towards building pervasive intelligence encompassing urban as well as rural environments has paved the way for the Internet of Things (IoT), which has reshaped our regular lifestyle alleviating the dependence on wired communication systems since its inception. The inexorable advancement in low to ultra-low power electronics have steered the rapid growth of the IoT platform expanding into several application fields. With the ongoing implementation of 5G (Fifth generation) and the emergence of 6G (Sixth generation) wireless technology on the horizon, the explosive growth of IoT connected devices reinforces the requirement of a robust and reliable power solution for the deployed wireless communication platforms. Utilizing distributed clean energy sources, especially the ubiquitous mechanical energy available in environment through dedicated transducers in the form of vibration energy harvesters (VEHs) to power the IoT-based wireless sensor platforms is a sought after alternatives to batteries in the forthcoming IoT applications. The potential of the resonant/linear VEHs have been limited owing to the narrow operable frequency bandwidth as well as due to the lack of intelligent device designs that aids to yield large electrical power from the provided mechanical energy. In this thesis, a concertina shaped linear VEH spring architecture has been exploited to instigate large amplitudes of oscillation, which aids to yield a high power density (455.6μW/cm3g2) at resonance from a relatively small device footprint. From the application perspective, this concertina-VEH has been utilized to power the electronics interface and enhance the performance of a NFC (Near Field Communication) based wireless sensor platform which offers the benefits of low power consumption and on call data acquisition through this short range NFC based communication protocol. Such a robust autonomous wireless sensing platform offers the potential to be used in a large number of IoT based applications. Despite of the large deliverable power obtained from the resonant VEH, the energy extraction drops dramatically as the excitation frequency deviates from the resonance condition, which is inevitable owing to the random nature of vibrations. A novel broadband VEH with tapered spring geometry has been developed as a part of this thesis to address this issue. Nonlinear restoring forces arising from the stretched springs enables the VEH to generate large power over a considerably wide bandwidth (45Hz of hysteresis width that is the difference of the jump down and jump up frequency with 1g excitation amplitude) of operable frequencies. Suitable power management strategies have been proposed to enhance the energy extraction capabilities. The nonlinear VEH has been successfully used to harness mechanical energy from the broadband vibrations of a car; the extracted energy is fed to a wireless sensor platform that reports on ambient temperature and humidity. This self-powered sensing system opens up the scope for exploiting this technology for monitoring food and medicinal quality during transportation while the VEH extracts mechanical energy from the transporting vehicle and perpetually powers the wireless sensor node. Multiple nonlinearities arising from the stretching of the VEH spring as well as from the interaction of repulsive magnets have been introduced into the energy harvester, which gives rise to coexisting multiple energy branches. Not all of these energy states are achieved through the typical excitation frequency routine, some of these energy states are rather hidden. Experimentally a route to achieve these hidden energy branches have been explored in this work. Suitable frequency routines have been designed to achieve and sustain these higher energy states. A useful graphical representation has been introduced in the form of ‘eye diagrams’ that essentially estimates the transaction of energy from mechanical to electrical domain, and provides deep insight of the dynamical features of each energy branches, based on time resolved measurements of acceleration and voltage. A mathematical model has been developed to investigate the intricate complexities of the nonlinear system, which supports the experimental findings. One of the major impediments in miniaturizing high-efficiency macroscale VEHs into MEMS (Micro-Electro-Mechanical-System) scale is the lack of matured technology for the CMOS (Complementary-Metal-Oxide-Semiconductor) compatible integration of magnets and the adverse effect of scaling on the permanent hard magnets. A part of the presented work investigates the effect of patterning continuous thin films of magnets into micromagnet array. With detailed analytical framework and exhaustive finite element analysis, the shape, size and distribution of these micromagnets have been optimized to maximize the stray magnetic field emanating from each edge of these magnets. Novel MEMS device topologies comprising of linear/nonlinear MEMS springs, micromagnet arrays and copper microcoil have been proposed which systematically maximizes the electromagnetic interaction between the micromagnets and the integrated coil that in turn translates into large deliverable power. In addition to the developed device prototypes and demonstrations, this thesis further provides a firm roadmap that highlights the potential routes for enhancing the energy harvesting capabilities through highly integrated MEMS scale VEHs as well as for improving system level integration to establish these VEHs as a reliable and sustainable alternative of batteries in IoT applications.
- ItemDevelopment and characterisation of macro-disc and micro-band electrodes for electrochemical sensing applications(University College Cork, 2022) Madden, Julia; Galvin, Paul; O'Riordan, Alan; Thompson, Michael; Science Foundation Ireland; Electronic Components and Systems for European LeadershipThe aim of this PhD thesis was to investigate potential next generation sensor platforms for electrochemical biosensor developments, specifically towards health monitoring applications. With increasing interest in the integration of miniaturised electrodes with minimally invasive and wearable devices, this thesis sought to explore electrodes fabricated using three different technologies for the construction of electrochemical biosensors: Silicon microfabrication, Laser scribing, and dispense printing. The first experimental section aimed to investigate the use of a single ultramicroband electrode fabricated on silicon for mediator-free glucose monitoring in bio-fluid environments. Six ultramicroband electrodes, a counter electrode and reference electrode were fabricated using standard microfabrication methods i.e. lithography and etching techniques. Glucose oxidase was selected as a model enzyme to attach onto a platinum modified gold microband electrode by electropolymerisation with an o-phenylenediamine/ß-cyclodextrin layer. The resulting microband biosensor demonstrated on-chip glucose detection in buffer based media. When applied to foetal bovine serum the sensor displayed a reduced sensitivity. The second experimental section explores the use of laser-scribed graphitic carbon for flexible sensing applications. A facile fabrication method was assessed involving electrodeposition of platinum followed by two casting steps to functionalise electrodes. This study examined the chronoamperometric response of the enzymatic lactate sensor whilst the flexible polyimide substrates were fixed at a curvature (K) of 0.14 mm-1. No noticeable change in signal response was observed in comparison to calibrations obtained with a flat substrate (K=0 mm-1), suggesting potential opportunities for sensor attachment or integration with oral-care products such as mouth swabs and mouth guards. Both laser scribed graphitic carbon and Ag/AgCl modified-laser scribed graphitic carbon were examined as reference electrodes for chronoamperometric lactate measurements. This device was applied for measuring lactate concentrations in artificial saliva and diluted sterile human serum. Finally, this study investigates the potential for a low cost additive printing tool to enable the fabrication of electrochemical sensor devices. To do this, electrodes were designed and printed onto polyimide substrates. Reproducibility between electrode dimensions was assessed using 3D microscopy. Standard electrochemical characterisation techniques were employed to study the reproducibility between electrode electrochemical response. Functionality was also assessed whilst electrodes were fixed were fixed at a curvature (K) of 0.14 mm-1. Finally, a simple casting approach was applied to the dispense printed working electrode to construct a lactate biosensor for a proof of concept electrochemical sensor demonstration.
- ItemDevelopment 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 LeadershipThe 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.
- ItemThin film magnetics for integrated magnetic nano-structures(University College Cork, 2022-11-01) Cronin, Darragh; McCloskey, Paul; O Mathuna, Cian; Masood, Ansar; Science Foundation IrelandThe 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.
- ItemDesign 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 IrelandNowadays, 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.