6,046 research outputs found

    Ultra-low power mixed-signal frontend for wearable EEGs

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    Electronics circuits are ubiquitous in daily life, aided by advancements in the chip design industry, leading to miniaturised solutions for typical day to day problems. One of the critical healthcare areas helped by this advancement in technology is electroencephalography (EEG). EEG is a non-invasive method of tracking a person's brain waves, and a crucial tool in several healthcare contexts, including epilepsy and sleep disorders. Current ambulatory EEG systems still suffer from limitations that affect their usability. Furthermore, many patients admitted to emergency departments (ED) for a neurological disorder like altered mental status or seizures, would remain undiagnosed hours to days after admission, which leads to an elevated rate of death compared to other conditions. Conducting a thorough EEG monitoring in early-stage could prevent further damage to the brain and avoid high mortality. But lack of portability and ease of access results in a long wait time for the prescribed patients. All real signals are analogue in nature, including brainwaves sensed by EEG systems. For converting the EEG signal into digital for further processing, a truly wearable EEG has to have an analogue mixed-signal front-end (AFE). This research aims to define the specifications for building a custom AFE for the EEG recording and use that to review the suitability of the architectures available in the literature. Another critical task is to provide new architectures that can meet the developed specifications for EEG monitoring and can be used in epilepsy diagnosis, sleep monitoring, drowsiness detection and depression study. The thesis starts with a preview on EEG technology and available methods of brainwaves recording. It further expands to design requirements for the AFE, with a discussion about critical issues that need resolving. Three new continuous-time capacitive feedback chopped amplifier designs are proposed. A novel calibration loop for setting the accurate value for a pseudo-resistor, which is a crucial block in the proposed topology, is also discussed. This pseudoresistor calibration loop achieved the resistor variation of under 8.25%. The thesis also presents a new design of a curvature corrected bandgap, as well as a novel DDA based fourth-order Sallen-Key filter. A modified sensor frontend architecture is then proposed, along with a detailed analysis of its implementation. Measurement results of the AFE are finally presented. The AFE consumed a total power of 3.2A (including ADC, amplifier, filter, and current generation circuitry) with the overall integrated input-referred noise of 0.87V-rms in the frequency band of 0.5-50Hz. Measurement results confirmed that only the proposed AFE achieved all defined specifications for the wearable EEG system with the smallest power consumption than state-of-art architectures that meet few but not all specifications. The AFE also achieved a CMRR of 131.62dB, which is higher than any studied architectures.Open Acces

    Characterization of Dielectric Barrier Discharge Plasma Actuators: Logarithmic Thrust-Voltage Quadratic Relationship

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    Results of thrust measurements of dielectric barrier discharge plasma actuators are presented. The test setup, measurement, and data processing methodology that were developed in prior work were used. The tests were conducted with high-density polyethylene actuators of three thicknesses. The applied voltage driving the actuators was a pure sinusoidal waveform. The test setup was a suspended actuator with a decoupling liquid interface. The tests were conducted at low ambient humidity. The thrust was measured with an analytical balance and the results were corrected for antithrust to isolate the plasma-generated thrust. Applying this approach resulted in smooth and repeatable data. It also enabled precise curve fitting that yielded quadratic relations between the plasma thrust and voltage in loglog space at constant frequencies. The results contrast power law relationships developed in literature that now appear to be an approximation only over a limited voltage range

    Development of reduced-scale tests for HTLS substation connectors

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    Power distribution networks face the upcoming challenge of managing the increase of power demand predicted worldwide. Power grid capacity is limited by the number of lines deployed and their characteristics, including conductor section, spacing, or number of phases, among others. Building new lines is costly and faces population opposition in many places. Therefore, a new conductor technology designed to upgrade the existing power lines has arisen. This technology, known as High Temperature Low-Sag (HTLS), permits the rise of capacity of existing power lines without modifying the supporting structures. Nowadays, the conductor technology is mature and under commercialization. But, there is the need to design and assess the behaviour of some auxiliary accessories needed to operate power lines equipped with HTLS conductors. Specifically, the substation connector industry is still developing HTLS substation connectors. From all the design process, the validation of the performance of these products is still a milestone. Currently, the tests performed to hardware for power lines are costly in terms of required infrastructures, testing time, power requirements, monetary cost and environmental affectation. Moreover, many of these tests can only be performed in few facilities all around the world. Furthermore, from an industrial scope, there is a growing interest to obtain the data of such tests in onsite industrial laboratories. Thus, this thesis develops a set of reduced-scale tests equivalent to the ones performed on full-scale connectors to validate the performance of the new designs. This thesis also performs a critical review of some of the methodologies that currently are being applied to assess products lifetime, and proposes the use of modern approaches. Concluding, this document aims to develop a series of test procedures that provide data about the validity of the newly required substation connectors designs in a cheaper, faster, and environmentally-friendlier way, whilst allowing to test the connectors in industrial laboratories, which have much less requirements than those of the full-scale test, since the later often require to be carried out in singular and scarce facilities.Las redes de distribución y transmisión de potencia se enfrentan al reto de manejar el incremento de demanda eléctrica previsto mundialmente. La capacidad de la red eléctrica está limitada por el número de líneas instaladas y sus características. Esto incluye, la sección del conductor, espaciado o número de fases, entre otros. La construcción de nuevas líneas es cara y en muchos casos imposible debido a la enorme oposición a la que se enfrentan en muchos lugares del mundo. Por ello, en los últimos años una nueva tecnología de conductores ha empezado a tomar importancia. Estos conectores conocidos como HTLS (alta temperatura baja flecha), permiten el aumento de la capacidad de las líneas eléctricas existentes sin por ello tener que modificar las estructuras que las soportan. Hoy en día, esta tecnología está suficientemente madura para ser comercializada. Sin embargo, existe la necesidad de diseñar y validar el comportamiento de una serie de accesorios auxiliares para líneas eléctricas. Concretamente, la industria de los conectores de subestación está desarrollando sus productos para líneas HTLS. El proceso de validación de estos conectores es aún un hito por alcanzar. Por el momento, los ensayos realizados sobre aparamenta para líneas eléctricas son costosos en términos de infraestructuras necesarias, tiempo de ensayo, potencia requerida, coste económico e impacto medioambiental. Además, muchos de estos ensayos sólo pueden llevarse a cabo en unas pocas instalaciones disponibles en todo el mundo. Por lo tanto, desde un punto de vista industrial, existe un creciente interés en obtener estos datos en laboratorios industriales. Por ello, esta tesis desarrolla un conjunto de ensayos a escala reducida equivalentes con los que hoy en día se realizan a escala real, con el fin de validar el rendimiento de los nuevos diseños de conector. Esta tesis también realiza una revisión crítica de algunas de las metodologías que hoy en día se llevan a cabo para estudiar el envejecimiento de los conectores de subestación. A su vez, propone el uso de metodologías más modernas para realizar dichos estudios. En conclusión, este documento desarrolla una serie de procedimientos de ensayo para validar los diseños de los nuevos desarrollos de conectores de subestación de una manera barata, rápida y respetuosa con el medio ambiente a la vez que permite el ensayo de dichos productos en laboratorios industriales

    Development of reduced-scale tests for HTLS substation connectors

    Get PDF
    Power distribution networks face the upcoming challenge of managing the increase of power demand predicted worldwide. Power grid capacity is limited by the number of lines deployed and their characteristics, including conductor section, spacing, or number of phases, among others. Building new lines is costly and faces population opposition in many places. Therefore, a new conductor technology designed to upgrade the existing power lines has arisen. This technology, known as High Temperature Low-Sag (HTLS), permits the rise of capacity of existing power lines without modifying the supporting structures. Nowadays, the conductor technology is mature and under commercialization. But, there is the need to design and assess the behaviour of some auxiliary accessories needed to operate power lines equipped with HTLS conductors. Specifically, the substation connector industry is still developing HTLS substation connectors. From all the design process, the validation of the performance of these products is still a milestone. Currently, the tests performed to hardware for power lines are costly in terms of required infrastructures, testing time, power requirements, monetary cost and environmental affectation. Moreover, many of these tests can only be performed in few facilities all around the world. Furthermore, from an industrial scope, there is a growing interest to obtain the data of such tests in onsite industrial laboratories. Thus, this thesis develops a set of reduced-scale tests equivalent to the ones performed on full-scale connectors to validate the performance of the new designs. This thesis also performs a critical review of some of the methodologies that currently are being applied to assess products lifetime, and proposes the use of modern approaches. Concluding, this document aims to develop a series of test procedures that provide data about the validity of the newly required substation connectors designs in a cheaper, faster, and environmentally-friendlier way, whilst allowing to test the connectors in industrial laboratories, which have much less requirements than those of the full-scale test, since the later often require to be carried out in singular and scarce facilities.Las redes de distribución y transmisión de potencia se enfrentan al reto de manejar el incremento de demanda eléctrica previsto mundialmente. La capacidad de la red eléctrica está limitada por el número de líneas instaladas y sus características. Esto incluye, la sección del conductor, espaciado o número de fases, entre otros. La construcción de nuevas líneas es cara y en muchos casos imposible debido a la enorme oposición a la que se enfrentan en muchos lugares del mundo. Por ello, en los últimos años una nueva tecnología de conductores ha empezado a tomar importancia. Estos conectores conocidos como HTLS (alta temperatura baja flecha), permiten el aumento de la capacidad de las líneas eléctricas existentes sin por ello tener que modificar las estructuras que las soportan. Hoy en día, esta tecnología está suficientemente madura para ser comercializada. Sin embargo, existe la necesidad de diseñar y validar el comportamiento de una serie de accesorios auxiliares para líneas eléctricas. Concretamente, la industria de los conectores de subestación está desarrollando sus productos para líneas HTLS. El proceso de validación de estos conectores es aún un hito por alcanzar. Por el momento, los ensayos realizados sobre aparamenta para líneas eléctricas son costosos en términos de infraestructuras necesarias, tiempo de ensayo, potencia requerida, coste económico e impacto medioambiental. Además, muchos de estos ensayos sólo pueden llevarse a cabo en unas pocas instalaciones disponibles en todo el mundo. Por lo tanto, desde un punto de vista industrial, existe un creciente interés en obtener estos datos en laboratorios industriales. Por ello, esta tesis desarrolla un conjunto de ensayos a escala reducida equivalentes con los que hoy en día se realizan a escala real, con el fin de validar el rendimiento de los nuevos diseños de conector. Esta tesis también realiza una revisión crítica de algunas de las metodologías que hoy en día se llevan a cabo para estudiar el envejecimiento de los conectores de subestación. A su vez, propone el uso de metodologías más modernas para realizar dichos estudios. En conclusión, este documento desarrolla una serie de procedimientos de ensayo para validar los diseños de los nuevos desarrollos de conectores de subestación de una manera barata, rápida y respetuosa con el medio ambiente a la vez que permite el ensayo de dichos productos en laboratorios industriales.Postprint (published version

    3D mesh processing using GAMer 2 to enable reaction-diffusion simulations in realistic cellular geometries

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    Recent advances in electron microscopy have enabled the imaging of single cells in 3D at nanometer length scale resolutions. An uncharted frontier for in silico biology is the ability to simulate cellular processes using these observed geometries. Enabling such simulations requires watertight meshing of electron micrograph images into 3D volume meshes, which can then form the basis of computer simulations of such processes using numerical techniques such as the Finite Element Method. In this paper, we describe the use of our recently rewritten mesh processing software, GAMer 2, to bridge the gap between poorly conditioned meshes generated from segmented micrographs and boundary marked tetrahedral meshes which are compatible with simulation. We demonstrate the application of a workflow using GAMer 2 to a series of electron micrographs of neuronal dendrite morphology explored at three different length scales and show that the resulting meshes are suitable for finite element simulations. This work is an important step towards making physical simulations of biological processes in realistic geometries routine. Innovations in algorithms to reconstruct and simulate cellular length scale phenomena based on emerging structural data will enable realistic physical models and advance discovery at the interface of geometry and cellular processes. We posit that a new frontier at the intersection of computational technologies and single cell biology is now open.Comment: 39 pages, 14 figures. High resolution figures and supplemental movies available upon reques

    Modification of a Commercial Nanoindentation System for measurement of hysteresis cycles under mechanical load in polycrystalline ferroelectric films

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    A commercial hardness-tester by nanoindentation was modified to use metallic indenter tips for the measurement of hysteresis cycles of ferroelectric films under mechanical load and with high lateral resolution. A novel semi-automatic charge integrating module was developed to this aim. LabVIEW 8.6 graphical programming environment was used to control the data acquisition system (DAS), the sinusoidal high voltage generator (± 300V) and the charge integrating module in the measurement of the loops. The software also provides data correction due to non-ferroelectric-switching contributions to obtain reliable remanent polarization (Pr) and coercive field (Ec) values. It also displays the loops both in polarization-field (P-E) and current density-field (J-E) modes. The experimental set-up was validated with measurements on dense PZT films (10μm) on platinised Si substrates. Coherent cycles are obtained using the novel semi-automatic charge integrator, the classical Sawyer and Tower circuit and using an electrometer. Under low indentation load causing quasi-elastic strain, the loops do not show any artifact.CSIC-PIE#201060E069Peer reviewe

    Integrated Circuits for Programming Flash Memories in Portable Applications

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    Smart devices such as smart grids, smart home devices, etc. are infrastructure systems that connect the world around us more than before. These devices can communicate with each other and help us manage our environment. This concept is called the Internet of Things (IoT). Not many smart nodes exist that are both low-power and programmable. Floating-gate (FG) transistors could be used to create adaptive sensor nodes by providing programmable bias currents. FG transistors are mostly used in digital applications like Flash memories. However, FG transistors can be used in analog applications, too. Unfortunately, due to the expensive infrastructure required for programming these transistors, they have not been economical to be used in portable applications. In this work, we present low-power approaches to programming FG transistors which make them a good candidate to be employed in future wireless sensor nodes and portable systems. First, we focus on the design of low-power circuits which can be used in programming the FG transistors such as high-voltage charge pumps, low-drop-out regulators, and voltage reference cells. Then, to achieve the goal of reducing the power consumption in programmable sensor nodes and reducing the programming infrastructure, we present a method to program FG transistors using negative voltages. We also present charge-pump structures to generate the necessary negative voltages for programming in this new configuration

    Techniques for Generating Centimetric Drops in Microgravity and Application to Cavitation Studies

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    This paper describes the techniques and physical parameters used to produce stable centimetric water drops in microgravity, and to study single cavitation bubbles inside such drops (Parabolic Flight Campaigns, European Space Agency ESA). While the main scientific results have been presented in a previous paper, we shall herein provide the necessary technical background, with potential applications to other experiments. First, we present an original method to produce and capture large stable drops in microgravity. This technique succeeded in generating quasi-spherical water drops with volumes up to 8 ml, despite the residual g-jitter. We find that the equilibrium of the drops is essentially dictated by the ratio between the drop volume and the contact surface used to capture the drop, and formulate a simple stability criterion. In a second part, we present a setup for creating and studying single cavitation bubbles inside those drops. In addition, we analyze the influence of the bubble size and position on the drop behaviour after collapse, i.e. jets and surface perturbations
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