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Novel Computing Paradigms using Oscillators
This dissertation is concerned with new ways of using oscillators to perform computational tasks. Specifically, it introduces methods for building finite state machines (for general-purpose Boolean computation) as well as Ising machines (for solving combinatorial optimization problems) using coupled oscillator networks.But firstly, why oscillators? Why use them for computation?An important reason is simply that oscillators are fascinating. Coupled oscillator systems often display intriguing synchronization phenomena where spontaneous patterns arise. From the synchronous flashing of fireflies to Huygens' clocks ticking in unison, from the molecular mechanism of circadian rhythms to the phase patterns in oscillatory neural circuits, the observation and study of synchronization in coupled oscillators has a long and rich history. Engineers across many disciplines have also taken inspiration from these phenomena, e.g., to design high-performance radio frequency communication circuits and optical lasers. To be able to contribute to the study of coupled oscillators and leverage them in novel paradigms of computing is without question an interesting andfulfilling quest in and of itself.Moreover, as Moore's Law nears its limits, new computing paradigms that are different from mere conventional complementary metal–oxide–semiconductor (CMOS) scaling have become an important area of exploration. One broad direction aims to improve CMOS performance using device technology such as fin field-effect transistors (FinFET) and gate-all-around (GAA) FETs. Other new computing schemes are based on non-CMOS material and device technology, e.g., graphene, carbon nanotubes, memristive devices, optical devices, etc.. Another growing trend in both academia and industry is to build digital application-specific integrated circuits (ASIC) suitable for speeding up certain computational tasks, often leveraging the parallel nature of unconventional non-von Neumann architectures. These schemes seek to circumvent the limitations posed at the device level through innovations at the system/architecture level.Our work on oscillator-based computation represents a direction that is different from the above and features several points of novelty and attractiveness. Firstly, it makes meaningful use of nonlinear dynamical phenomena to tackle well-defined computational tasks that span analog and digital domains. It also differs from conventional computational systems at the fundamental logic encoding level, using timing/phase of oscillation as opposed to voltage levels to represent logic values. These differences bring about several advantages. The change of logic encoding scheme has several device- and system-level benefits related to noise immunity and interference resistance. The use of nonlinear oscillator dynamics allows our systems to address problems difficult for conventional digital computation. Furthermore, our schemes are amenable to realizations using almost all types of oscillators, allowing a wide variety of devices from multiple physical domains to serve as the substrate for computing. This ability to leverage emerging multiphysics devices need not put off the realization of our ideas far into the future. Instead, implementations using well-established circuit technology are already both practical and attractive.This work also differs from all past work on oscillator-based computing, which mostly focuses on specialized image preprocessing tasks, such as edge detection, image segmentation and pattern recognition. Perhaps its most unique feature is that our systems use transitions between analog and digital modes of operation --- unlike other existing schemes that simply couple oscillators and let their phases settle to a continuum of values, we use a special type of injection locking to make each oscillator settle to one of the several well-defined multistable phase-locked states, which we use to encode logic values for computation. Our schemes of oscillator-based Boolean and Ising computation are built upon this digitization of phase; they expand the scope of oscillator-based computing significantly.Our ideas are built on years of past research in the modelling, simulation and analysis of oscillators. While there is a considerable amount of literature (arguably since Christiaan Huygens wrote about his observation of synchronized pendulum clocks in the 17th century) analyzing the synchronization phenomenon from different perspectives at different levels, we have been able to further develop the theory of injection locking, connecting the dots to find a path of analysis that starts from the low-level differential equations of individual oscillators and arrives at phase-based models and energy landscapes of coupled oscillator systems. This theoretical scaffolding is able not only to explain the operation of oscillator-based systems, but also to serve as the basis for simulation and design tools. Building on this, we explore the practical design of our proposed systems, demonstrate working prototypes, as well as develop the techniques, tools and methodologies essential for the process
Heartbeat Optical Coherence Tomography
__Abstract__
Coronary artery disease (CAD) is a manifestation of atherosclerosis, a systemic inflammatory disease of
the arteries that causes the formation of plaques in the artery walls. Different plaques may give rise to
different symptoms: a gradual narrowing (stenosis) of the vessel by growth of a fibrous or calcific plaque
will cause chest pain (due to cardiac ischemia) upon exertion, a condition called stable CAD. Sudden
onset of chest pain, or chest pain at rest, is a symptom of unstable CAD or acute coronary syndrome
(ACS), which is associated with thrombus formation on plaques, mostly due to rupture of a lipid-core
lesion. The most severe form of this disease may lead to a myocardial infarction or heart attack
Finite-control-set model predictive control of axially laminated flux-switching permanent magent machine with extended voltage space vectors
University of Technology Sydney. Faculty of Engineering and Information Technology.The Flux-switching permanent magnet machine (FSPMM) has recently attracted considerable interest for high performance drive applications due to their high torque and high power density features. The laminations of traditional FSPMMs are radially laminated, i.e. steel sheets are laminated perpendicular to the shaft axis. Due to the nonlinear magnetic path, the radial laminations can have serious partial magnetic saturation at the edges/tips of stator teeth or rotor poles. The rated frequency of FSPMMs is usually much higher than traditional rotor-inserted PM machines at a given speed. In this case, the core loss of FSPMMs becomes evident especially beyond the rated speed, which leads to decrease of output power, torque/power density and efficiency.
The reluctance motor with axially laminated rotor has received growing interest in recent years. This type of motor can achieve a higher torque density compared with segmented rotors and flux-barrier rotors. In this thesis, an axially laminated flux-switching permanent magnet machine (ALFSPMM) with HiB grain oriented silicon steel stator and rotor cores is proposed. The HiB silicon steel features high permeability and low specific core loss, and as a result, the total power loss of proposed motor is much lower than the conventional FSPMMs. The detailed fabrication procedures are presented. The theoretical characteristics of ALFSPMM are calculated by 2D finite element method (FEM). Experimental measurements of the prototype machine are presented to validate the FEM calculation.
On the machine control side, the direct torque control (DTC) is one of the most popular control algorithms. It features simple structure and fast dynamic response. However, the performance of DTC in terms of torque and flux ripples and drive system efficiency is unsatisfactory since the voltage space vector (VSV) is selected heuristically. Recently, the finite-control-set model predictive direct torque control (FCS-MPDTC) has been developed as a simple and promising control technique to overcome these problems. The FCS-MPDTC still suffers from relatively high torque and flux ripples due to the limited number of VSVs.
This thesis proposes a novel FCS-MPDTC with an extended set of twenty modulated VSVs, which are formed by eight basic VSVs and twelve extended VSVs by modulating eight basic VSVs with fixed duty ratio. To mitigate the computational burden caused by the increased number of VSVs, a pre-selective scheme is designed for the proposed FCS-MPDTC to filter out the impractical VSVs. The drive system efficiency is also investigated. The theory and simulation are validated by experimental results on the ALFSPMM prototype
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