A Novel Power-Efficient Wireless Multi-channel Recording System for the Telemonitoring of Electroencephalography (EEG)

This research introduces the development of a novel EEG recording system that is modular, batteryless, and wireless (untethered) with the supporting theoretical foundation in wireless communications and related design elements and circuitry. Its modular construct overcomes the EEG scaling problem and makes it easier for reconfiguring the hardware design in terms of the number and placement of electrodes and type of standard EEG system contemplated for use. In this development, portability, lightweight, and applicability to other clinical applications that rely on EEG data are sought. Due to printer tolerance, the 3D printed cap consists of 61 electrode placements. This recording capacity can however extend from 21 (as in the international 10-20 systems) up to 61 EEG channels at sample rates ranging from 250 to 1000 Hz and the transfer of the raw EEG signal using a standard allocated frequency as a data carrier. The main objectives of this dissertation are to (1) eliminate the need for heavy mounted batteries, (2) overcome the requirement for bulky power systems, and (3) avoid the use of data cables to untether the EEG system from the subject for a more practical and less restrictive setting. Unpredictability and temporal variations of the EEG input make developing a battery-free and cable-free EEG reading device challenging. Professional high-quality and high-resolution analog front ends are required to capture non-stationary EEG signals at microvolt levels. The primary components of the proposed setup are the wireless power transmission unit, which consists of a power amplifier, highly efficient resonant-inductive link, rectification, regulation, and power management units, as well as the analog front end, which consists of an analog to digital converter, pre-amplification unit, filtering unit, host microprocessor, and the wireless communication unit. These must all be compatible with the rest of the system and must use the least amount of power possible while minimizing the presence of noise and the attenuation of the recorded signal A highly efficient resonant-inductive coupling link is developed to decrease power transmission dissipation. Magnetized materials were utilized to steer electromagnetic flux and decrease route and medium loss while transmitting the required energy with low dissipation. Signal pre-amplification is handled by the front-end active electrodes. Standard bio-amplifier design approaches are combined to accomplish this purpose, and a thorough investigation of the optimum ADC, microcontroller, and transceiver units has been carried out. We can minimize overall system weight and power consumption by employing battery-less and cable-free EEG readout system designs, consequently giving patients more comfort and freedom of movement. Similarly, the solutions are designed to match the performance of medical-grade equipment. The captured electrical impulses using the proposed setup can be stored for various uses, including classification, prediction, 3D source localization, and for monitoring and diagnosing different brain disorders. All the proposed designs and supporting mathematical derivations were validated through empirical and software-simulated experiments. Many of the proposed designs, including the 3D head cap, the wireless power transmission unit, and the pre-amplification unit, are already fabricated, and the schematic circuits and simulation results were based on Spice, Altium, and high-frequency structure simulator (HFSS) software. The fully integrated head cap to be fabricated would require embedding the active electrodes into the 3D headset and applying current technological advances to miniaturize some of the design elements developed in this dissertation

Superconducting wireless power transfer for electric vehicles

Electric vehicles (EVs) are an important pillar for the transition towards a cleaner and more sustainable future as renewable energy can penetrate into the transportation section and act as energy storage to cope with the intermittent supply of such energy sources. EVs have recently been significantly developed in terms of both performance and drive range. Various models are already commercially available, and the number of EVs on roads increases rapidly. Rather than being limited by physical cable connections, the wireless (inductive) link creates the opportunity of dynamic charging – charging while driving. Once realised, EVs will no longer be limited by their achievable range and the requirement for battery capacity will be greatly reduced. However, wireless charging systems are limited in their transfer distance and power density. Such drawbacks can be alleviated through high-temperature superconductors (HTS) and their increased current carrying capacity, which can substitute conventionally used copper coils in the charging pads. This thesis investigates the effectiveness of wireless power transfer (WPT) systems as a whole and when HTS coils are used as well as HTS performance at operating frequencies commonly used in WPT-systems. Initially, the fundamentals of superconductivity are outlined to give some background on how such conductors can help tackle problems occurring in WPT-systems and how their behaviour can be simulated. Subsequently, key technical components of wireless charging are summarised and compared, such as compensation topologies, coil design and communication. In addition, health and safety concerns regarding wireless charging are addressed, as well as their relevant standards. Economically, the costs of a wide range of wireless charging systems has also been summarised and compared. To explore the benefits of WPT-system for EVs, a force-based vehicle model is coupled with an extended battery model to simulate the impact of wireless charging on the state of charge of the accumulator sub-system. In total, three different scenarios, i.e. urban, highway and combined driving are presented. The trade-off between having a standalone charging option versus combined dynamic (or on-road charging) and quasi-dynamic (stationary charging in a dynamic environment) wireless charging is outlined and minimum system requirements, such as charging power levels and road coverage, for unlimited range are established. Furthermore, the effects of external factors such as ambient temperature, battery age and wireless transfer efficiency are investigated. It is shown that employing combined charging at medium power levels is sufficient to achieve unlimited range compared to high power requirements for standalone charging. HTS coils show great potential to enhance the WPT-system performance with high current-carrying capability and extremely low losses under certain conditions. However, HTS coils exhibit highly nonlinear loss characteristics, especially at high frequencies (above 1 kHz), which negatively influence the overall system performance. To investigate the improvements, copper, HTS and hybrid wireless charging systems in the frequency range of 11-85 kHz are experimentally tested. Results are compared with finite element analysis (FEA) simulations, which have been combined with electrical circuit models for performance analysis. The measurements and modelling results show good agreement for the WPT-system and HTS charging systems have a much higher transfer efficiency than copper at frequencies below 50 kHz. As the operating frequency increases towards 100 kHz, the performance of HTS systems deteriorates and becomes comparable to copper systems. Similar results are obtained from hybrid systems with a mixture of HTS and copper coils, either as transmitting or receiving coils. Nevertheless, it has been demonstrated that HTS significantly improves the transfer efficiency of wireless charging within a certain range of frequencies. The AC losses occurring in HTS coils, particularly transport current loss, magnetisation loss and combined loss, at high frequencies are studied further. A multilayer 2D axisymmetric coil model based on H-formulation is proposed and validated by experimental results as the HTS film layer is inapplicable at such frequencies. Three of the most commonly employed coil configurations, namely: double pancake, solenoid and circular spiral are examined. While spiral coils experience the highest transport current loss, solenoid coils are subject to the highest magnetisation loss due to the overall distribution of the turns. Furthermore, a transition frequency is defined for each coil when losses in the copper layer exceed the HTS losses. It is much lower for coils due to the interactions between the different turns compared to single HTS tapes. At higher frequencies, the range of magnetic field densities, causing a shift where the highest losses occur, decreases until losses in the copper stabilisers always dominate. In addition, case studies investigating the suitability of HTS-WPT are proposed. Lastly, methods to reduce AC losses of HTS coils are investigated with particular focus on flux diverters, which have been used for low frequency superconducting applications but their effectiveness at high frequencies is unexplored. Therefore, the impact of flux diverters on HTS double pancake coils operating at high frequencies up to 85 kHz is researched. Various geometric characteristics of the flux diverter are investigated such as air gap between diverter and coil, width and thickness. An FEA-model was used to examine the coil and diverter losses at such frequencies and different load factors between 0.1 and 0.8. It is demonstrated that flux diverters are a viable option to reduce the coil losses even at high frequencies and the width of the coil has the biggest impact on the loss reduction. In general, flux diverters are more suitable for applications using high load factors. Lastly, the impact of the diverter in terms of magnetic field distribution above the coil and overall loss distribution in the HTS coil was examined