Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

Diseño y construcción de un generador de plasma para aplicaciones en cirugía

Tesis que describe el diseño y pruebas de un sistema electrónico para la generación de plasma para uso en cirugíasEn los procesos quirúrgicos es importante contar con herramientas de corte que permitan realizar ablaciones de manera esterilizada y con el mínimo daño al tejido colateral. La electrocirugía surge como una alternativa al bisturí la cual, además de realizar el corte, permite cauterizar y reducir cortes accidentales a los cirujanos. Sin embargo, una de las desventajas de la electrocirugía convencional, es la alta temperatura que alcanza (400 °C), la cual causa daños considerables al tejido circundante. Como alternativa a esto se ha planteado la ablación utilizando plasma frío, con esta técnica se realizan ablaciones a temperaturas entre 40 °C y 70 °C, reduciendo el daño colateral y agilizando la recuperación de los pacientes. Sin embargo, esta técnica aún está en desarrollo, diversos centros de investigación se encuentran desarrollando nuevas aplicaciones y técnicas de uso. En México, sin embargo, es prácticamente nula la aplicación debido a la falta de conocimiento de la técnica y de equipos que permitan generar plasma a diversos voltajes, corrientes y frecuencias. En esta tesis se presenta el estudio teórico y experimental para el diseño y construcción de un generador de plasma, cuyo propósito es la generación de plasma mediante solución conductora, con el objetivo de realizar el corte y cauterización de tejido animal. Para la implementación del generador se construyó una fuente de alto voltaje basada en la topología push pull, un rectificador de onda completa e inversor de puente completo. El generador de plasma realizado, puede suministrar voltajes hasta los 320 V RMS con una corriente máxima de 330 mA RMS, a una frecuencia que se encuentra en el intervalo de 100 a 150 kHz. Se elaboraron pruebas en donde se comprobó el comportamiento del sistema, de acuerdo a los parámetros de diseño. En dichas pruebas se variaron los parámetros de voltaje y frecuencia y se logró determinar qué parámetros son óptimos para realizar un mejor corte al tejido utilizado. El prototipo demostró tener la potencia suficiente para formar plasma alrededor de los electrodos de la sonda empleada, sumergida en solución salina. Con este trabajo se logró obtener una herramienta para los investigadores interesados en utilizar plasma en procesos quirúrgicos, a bajo costo y con la posibilidad de manipular los parámetros de voltaje, corriente y frecuencia

NASA Tech Briefs Index, 1978

Approximately 601 announcements of new technology derived from the research and development activities of the National Aeronautics and Space Administration are presented. Emphasis is placed on information considered likely to be transferrable across industrial, regional, or disciplinary lines. Subject matter covered includes: electronic components and circuits; electron systems; physical sciences; materials; life sciences; mechanics; machinery; fabrication technology; and mathematics and information sciences

Investigating Ultrasound-Guided Autonomous Assistance during Robotic Minimally Invasive Surgery

Despite it being over twenty years since the first introduction of robotic surgical systems in common surgical practice, they are still far from widespread across all healthcare systems, surgical disciplines and procedures. At the same time, the systems that are used act as mere tele-manipulators with motion scaling and have yet to make use of the immense potential of their sensory data in providing autonomous assistance during surgery or perform tasks themselves in a semi-autonomous fashion. Equivalently, the potential of using intracorporeal imaging, particularly Ultrasound (US) during surgery for improved tumour localisation remains largely unused. Aside from the cost factors, this also has to do with the necessity of adequate training for scan interpretation and the difficulty of handling an US probe near the surgical sight. Additionally, the potential for automation that is being explored in extracorporeal US using serial manipulators does not yet translate into ultrasound-enabled autonomous assistance in a surgical robotic setting. Motivated by this research gap, this work explores means to enable autonomous intracorporeal ultrasound in a surgical robotic setting. Based around the the da Vinci Research Kit (dVRK), it first develops a surgical robotics platform that allows for precise evaluation of the robot’s performance using Infrared (IR) tracking technology. Based on this initial work, it then explores the possibility to provide autonomous ultrasound guidance during surgery. Therefore, it develops and assesses means to improve kinematic accuracy despite manipulator backlash as well as enabling adequate probe position with respect to the tissue surface and anatomy. Founded on the acquired anatomical information, this thesis explores the integration of a second robotic arm and its usage for autonomous assistance. Starting with an autonomously acquired tumor scan, the setup is extended and methods devised to enable the autonomous marking of margined tumor boundaries on the tissue surface both in a phantom as well as in an ex-vivo experiment on porcine liver. Moving towards increased autonomy, a novel minimally invasive High Intensity Focused Ultrasound (HIFUS) transducer is integrated into the robotic setup including a sensorised, water-filled membrane for sensing interaction forces with the tissue surface. For this purpose an extensive material characterisation is caried out, exploring different surface material pairings. Finally, the proposed system, including trajectory planning and a hybrid-force position control scheme are evaluated in a benchtop ultrasound phantom trial

NASA Tech Briefs Index 1978

Tech Briefs are short announcements of new technology derived from the research and development activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This Index to NASA Tech Briefs contains abstracts and four indexes -- subject, personal author, originating Center, and Tech Brief number -- for 1978 Tech Briefs

Numerical modelling of low temperature plasma

The intention of this thesis is to gain a better understanding of basic physical processes occurring in low temperature plasmas. This is achieved by applying both analytic and numerical models. Low temperature plasmas are found in both technological and astrophysical contexts. Three different situations are investigated: an instability in electronegative plasmas; electron avalanches during plasma initiation; and a phenomenon called the Critical Ionisation Velocity interaction. Industrial plasma discharges with electronegative gases are found to be unstable in certain conditions. Fluctuations in light emission, particle number densities and potential are observed. The instability has been reproduced in a variety of experiments. Reports from the experiments are discussed to characterise the key features of the instability. An, as yet un-considered, physical process that could explain the instability is introduced. The instability relies on the plasma's transparency to the electric field. This mechanism is investigated using simple zero-dimensional numerical and analytic models. The results from the models are compared to experimental results. The calculated frequencies are in good agreement with the experimental measurements. This shows that the instability mechanism described here is relevant. For the remaining two problems a three-dimensional particle model is constructed. This model calculates the trajectories of each individual particle. The potential field is solved self-consistently on a computational mesh. Poisson's equation is solved using a Multigrid technique. This iterative solution method uses many grids, of different resolutions, to smooth the error on all spatial scales. The mathematical foundation and details of the components of the Multigrid method are presented. Several test cases where analytic solutions of Poisson's equation exist are used to determine the accuracy of the solver. The implemented solver is found to be both efficient and accurate. Collisions are vitally important to the evolution of plasmas. The chemistry resulting from collisions is the reason why plasmas are so useful in technological applications. Electron collisions are included in the particle model using a Monte-Carlo technique. A basic method is given and several improvements are described. The most efficient combination of improvements is determined through a series of test cases. The error resulting from the collision selection process is characterised. Technological plasmas are formed from the electrical breakdown of a neutral gas. At atmospheric pressure the breakdown occurs as an electron avalanche. The particle model is used to simulate the nanosecond evolution of the avalanche from a single electron-ion pair. Special attention is paid to the inelastic collisions and the creation of metastables. The inelastic losses are used to estimate the photon emission from the electron avalanche. The Critical Ionisation Velocity phenomena is investigated using the particle model. When a neutral gas streams across a magnetised plasma the ionisation rate increases rapidly if the speed of the neutrals exceeds a critical value. Collisions between neutrals and positive ions create pockets of unbalanced negative charge. Electrons in these pockets are accelerated by their potential field and can reach energies capable of ionisation. The evolution of such an electron overdensity is simulated and their energy gain under different density and magnetic field conditions is calculated. The results from the simulation may explain the discrepancy between laboratory and space experiments

Comparing Gaussian and Bessel-Gauss beams for translating ultrafast laser ablation towards soft tissue surgery

The goal of this research was to further improve existing ultrafast laser surgery techniques. To do so, different beam shapes (Bessel-Gauss and Gaussian) were compared for performing ultrashort picosecond pulsed surgery on various soft biological tissues, with the goal of minimising collateral thermal damage. Initially, theoretical modelling was performed using OpticStudio to test axicons of various conical angles. A 20° axicon was selected, but unfortunately early tests on murine intestinal tissue indicated a lack of sufficient intensity to achieve plasma-mediated ablation of the tissue with the 6ps input pulses of 85 µJ energy. Subsequently, a reimaged setup was designed in OpticStudio to demagnify the beam by a factor of 1.4x. The ability of this demagnified Bessel-Gauss beam to perform plasma-mediated ablation of murine intestinal tissue was confirmed through histological analysis. Another setup was also designed to produce a Gaussian beam of equivalent spot size. These beams were then tested on porcine intestinal tissue using lower pulse repetition rates of 1, 2 and 3 kHz, with optimal ablation and thermal damage margins of less than 20 µm (confirmed through histological analysis) being achieved with the Bessel-Gauss beam for spatial pulse overlaps of 70%, while for the Gaussian beam the prominence of cavitation bubble formation at both 2 and 3 kHz inhibited the respective ablation processes at this same spatial pulse overlap. As the numbers of passes were increased, the Bessel-Gauss beam also showed a trend of increased ablation depths. This was attributed to its large depth of focus of over 1 mm, compared to the theoretical 48 µm depth of focus for the Gaussian beam. After characterisation of fixated, non-ablated porcine intestine sample surfaces to quantify the inhomogeneity, another set of ablation trials was performed at higher pulse repetition rates (5, 10 and 20 kHz) to test more clinically viable processes. For the Bessel-Gauss beam, spatial pulse overlaps of up to around 50% at 5, 10 and 20 kHz offered excellent thermal confinement (with damage margins of < 30 µm, < 50 µm and < 25 µm respectively) and shape control, but at 70% and greater pulse overlaps the ablated feature became hard to control despite good thermal confinement (< 40 µm). The Gaussian beam, while having the advantage of achieving plasma formation at lower input pulse energies, was again found to be more prone to undesirable cavitation effects. Cavitation bubbles were observed in the histology images for spatial pulse overlaps as low as 15% for 5 kHz and 30% for both 10 and 20 kHz. From the histology images it is clear to see that these effects became more pronounced as the pulse repetition rate was increased. Conversely, the more consistent spot size of the Bessel-Gauss beam across its longer focal depth resulted in a higher tolerance to cavitation bubble formation. This was also demonstrated by high-speed videos of the beams being scanned across porcine skin samples. This could be significant as it may allow for higher ablation rates. In addition, it could ease the design constraint of the maximum speed at which the beam can be scanned at the distal end of an endoscopic device. Despite this, both beams were able to achieve distinct ablation with high thermal confinement for certain parameters. This work further highlights fibre-delivered ultrashort laser pulses as a promising alternative to existing endoscopic tumour resection techniques, which carry a higher risk of bowel perforation.James Watt Scholarshi

Robotic Catheters for Beating Heart Surgery

Compliant and flexible cardiac catheters provide direct access to the inside of the heart via the vascular system without requiring clinicians to stop the heart or open the chest. However, the fast motion of the intracardiac structures makes it difficult to modify and repair the cardiac tissue in a controlled and safe manner. In addition, rigid robotic tools for beating heart surgery require the chest to be opened and the heart exposed, making the procedures highly invasive. The novel robotic catheter system presented here enables minimally invasive repair on the fast-moving structures inside the heart, like the mitral valve annulus, without the invasiveness or risks of stopped heart procedures. In this thesis, I investigate the development of 3D ultrasound-guided robotic catheters for beating heart surgery. First, the force and stiffness values of tissue structures in the left atrium are measured to develop design requirements for the system. This research shows that a catheter will experience contractile forces of 0.5 – 1.0 N and a mean tissue structure stiffness of approximately 0.1 N/mm while interacting with the mitral valve annulus. Next, this thesis presents the catheter system design, including force sensing, tissue resection, and ablation end effectors. In order to operate inside the beating heart, position and force control systems were developed to compensate for the catheter performance limitations of friction and deadzone backlash and evaluated with ex vivo and in vivo experiments. Through the addition of friction and deadzone compensation terms, the system is able to achieve position tracking with less than 1 mm RMS error and force tracking with 0.08 N RMS error under ultrasound image guidance. Finally, this thesis examines how the robotic catheter system enhances beating heart clinical procedures. Specifically, this system improves resection quality while reducing the forces experienced by the tissue by almost 80% and improves ablation performance by reducing contact resistance variations by 97% while applying a constant force on the moving tissue.Engineering and Applied Science