Browsing by Subject "Sensing"

Now showing 1 - 8 of 8
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    Active Target Localization and Tracking with Application to Robotic Environmental Monitoring
    (2015-09) Vander Hook, Joshua
    Thanks to advances in miniaturization, computing power, reliable sensors, and battery life, mobile robots are increasingly being used for a wide variety of environmental monitoring tasks. No longer confined to factory floors or controlled environments, robots for remote sensing in dangerous or hard-to-reach environments could provide the same scalability, precision, and reliability to environmental monitoring as they did to industrial applications. To enable this kind of long-term, reliable, autonomous mobile sensor deployment, algorithms which can ensure that the robots achieve their sensing tasks are required. In the first part of the thesis, we study the problem of using one or more mobile robots equipped with bearing sensors to locate a stationary target in minimum time. The problem requires optimizing the measurement locations of the robots to gather the required information about the target's location. In addition, when multiple robots collaborate, we include communication constraints in the path planning objective. Two formulations for this problem are studied. First, we study the offline problem of finding measurement trajectories when the true target location is known. Second, we study the online version and show how to adapt the offline solution to the situation when the target location is not known, while preserving the quality guarantees of the offline solution. In the second part of the thesis, we study the problem of locating multiple stationary targets using a single mobile robot. We formulate a novel coverage problem and provide two main results. We first study the problem of initializing consistent estimate of the targets' locations. These initial estimates are used to seed an active localization algorithm which is shown to localize the targets quickly. In a second formulation, we assume that the targets are within a set of polygonal regions, but have no further information about the distribution or number of targets in the environment. An algorithm is provided which can choose measurement locations to localize all the targets to within desired precision in near optimal time. In the third part of the thesis, we study the problem of using bearing information to track and capture a moving target. We present two formulations based on pursuit-evasion games. In the open plane, the objective is for a mobile robot to minimize the distance to a maneuvering target when only uncertain bearing information is available to the robot. Then, we study the problem of capturing the maneuvering target in a closed environment by moving close to it. We show that the size of the environment relative to the sensing noise determines if this is possible. HASH(0x7febe3ca4040) In addition to theoretical results, we present field studies of using one or more mobile robots to detect radio transmitters using these results. We show that the algorithms presented are suitable for use in monitoring invasive fish.
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    Atomic layer lithography of plasmonic nanogaps for enhanced light-matter interactions: fabrication and applications
    (2016-01) Chen, Xiaoshu
    Enhanced light-matter interactions at the nanometer scale have many potential applications, such as thin film sensing, enhanced Raman scattering, enhanced infrared absorption, particle manipulation, among others. Metal – insulator – metal nanogap structure is one of the most effective plasmonic devices for such applications since they are capable of generating the strongest light field enhancement inside the nanogap. However, current techniques to make such nanogap structures are either very expensive, slow, or lacking of control over nanogap size, pattern shape, and position. In this thesis, two wafer-scale fabrication methods are presented to address the challenges in fabrication. The fabricated devices are then used to demonstrate the above-mentioned applications. Atomic layer deposition is used in both methods to define the width of nanogap with angstrom resolution. The length, position, and shape of the nanogaps are precisely controlled in wafer scale by photolithography and metal deposition. A simple tape peeling and a template stripping process are used to expose the nanogaps. Nanogap devices with different designs are proved to support strong optical resonances in visible, near infrared, mid infrared, and terahertz-frequency regimes. By squeezing electromagnetic waves into nanometer wide gaps, huge field enhancement can be achieved inside the gaps. These novel fabrication methods can easily be duplicated and thus lead to broad studies and applications of the enhanced light-matter interactions.
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    Garment-Based Respiration And Pulse Oximetry Sensing Using A Stitched Sensor And Chest Mounted Pulse Oximetry Sensor
    (2023-08) Clarke, Megan
    Garment-based wearable devices have the potential to make on-body sensing of vital signs a more seamless part of everyday life. This research seeks to investigate a wearable chest-mounted stitched strain sensor and pulse oximeter for the purpose of developing a garment-based sensing device. A wearable or garment-based device could be used for long term or long distance monitoring a wearer’s respiratory health when regular access to healthcare is challenging due to distance, such as is the case in many rural communities. However, the effect of fit and sizing of a wearable device is a significant challenge when it comes to the balancing comfort and sensor accuracy needs in a wearable device. A stitched conductive thread sensor and an adapted pulse oximeter probe integrated into a chest-mounted mounted adjustable sensor belt were investigated to understand their performance relative to more typical sensing approaches. Two fit conditions were employed to measure effects on sensor performance and understand the challenges presented by garment-based sensing of respiratory signals. This research found that in general a tighter fit condition improved the performance of the stitched respiration sensor and chest mounted pulse oximeter, however sensor dropout greatly influenced both blood oxygen saturation (SpO₂) and beats-per-minute (BPM) data resulting in suboptimal readings. The stitched sensor was more accurate in measuring breath frequency than the comparison clinical device when fit was not optimized. As a result of this research, it is clear that the fit and sizing of a garment-based sensing device is a crucial factor in developing sensing garments suitable for everyday use.
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    Improving the Performance of Electroanalytical Devices for Sensing and Energy Storage
    (2016-01) Mousavi, Seyedeh Moloud
    My graduate research was focused on improving the performance and expanding the application of two categories electrochemical devices that are used in energy storage and sensing: electrochemical double-layer capacitors and ion-selective electrodes. The energy density of an electrochemical capacitor is determined by ½ CV2, where V is the potential difference between the plates of a capacitor and C is the capacitance density. Therefore, extending the operational voltage of such devices, which is limited by the electrochemical window of the electrolyte, can improve the device energy density. Optimizing the structure and improving electrochemical stability of electrolytes that can be utilized in electrochemical capacitors, was one of the goals of research presented in this thesis. Chapter 2 reviews the conventional methods for quantifying the electrochemical stability of electrolytes, and discusses their limitations. A new method for quantifying electrochemical stability of ionic liquids and electrolytes is suggested and several advantages of the proposed method is demonstrated for variety of systems. The effect of electrolyte structure on its electrochemical stability and accessible potential window is discussed in Chapter 3 and Chapter 4 highlights advantages of application of ionic liquids as electrolytes in electrochemical capacitors. Ion-selective electrodes, ISEs, are electrochemical sensors that determine the concentration of a wide range of ions and are used for billions of measurements in clinical, environmental, and chemical process analyses every year. However, two factors limit the application of ISEs in biological analyses: (1) Interference of biological molecules (2) Large sample volumes needed for ISE measurements. Recently, fluorophilic compounds have been applied in the ion-selective membrane of ISEs in an effort to reduce the interference of biological molecules. Chapters 5 to 7 show the reliability of sensing with fluorous-phase ion-selective electrodes in the environmental and biological samples. A part of my thesis research is focused on reducing the sample volume needed for detection with these sensors. This goal was achieved by development of highly fluorophilic electrolytes which were used to decrease the resistivity of the fluorous sensing membranes, allowing fabrication of fluorous-phase µ-ISEs and significantly decreasing the sample volume required for sensing.
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    Placement and motion planning algorithms for robotic sensing systems
    (2014-10) Tokekar, Pratap Rajkumar
    Recent technological advances are making it possible to build teams of sensors and robots that can sense data from hard-to-reach places at unprecedented spatio-temporal scales. Robotic sensing systems hold the potential to revolutionize a diverse collection of applications such as agriculture, environmental monitoring, climate studies, security and surveillance in the near future. In order to make full use of this technology, it is crucial to complement it with efficient algorithms that plan for the sensing in these systems. In this dissertation, we develop new sensor planning algorithms and present prototype robotic sensing systems.In the first part of this dissertation, we study two problems on placing stationary sensors to cover an environment. Our objective is to place the fewest number of sensors required to ensure that every point in the environment is covered. In the first problem, we say a point is covered if it is seen by sensors from all orientations. The environment is represented as a polygon and the sensors are modeled as omnidirectional cameras. Our formulation, which builds on the well-known art gallery problem, is motivated by practical applications such as visual inspection and video-conferencing where seeing objects from all sides is crucial. In the second problem, we study how to deploy bearing sensors in order to localize a target in the environment. The sensors measure noisy bearings towards the target which can be combined to localize the target. The uncertainty in localization is a function of the placement of the sensors relative to the target. For both problems we present (i) lower bounds on the number of sensors required for an optimal algorithm, and (ii) algorithms to place at most a constant times the optimal number of sensors. In the second part of this dissertation, we study motion planning problems for mobile sensors. We start by investigating how to plan the motion of a team of aerial robots tasked with tracking targets that are moving on the ground. We then study various coverage problems that arise in two environmental monitoring applications: using robotic boats to monitor radio-tagged invasive fish in lakes, and using ground and aerial robots for data collection in precision agriculture. We formulate the coverage problems based on constraints observed in practice. We also present the design of prototype robotic systems for these applications. In the final problem, we investigate how to optimize the low-level motion of the robots to minimize their energy consumption and extend the system lifetime.This dissertation makes progress towards building robotic sensing systems along two directions. We present algorithms with strong theoretical performance guarantees, often by proving that our algorithms are optimal or that their costs are at most a constant factor away from the optimal values. We also demonstrate the feasibility and applicability of our results through system implementation and with results from simulations and extensive field experiments.
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    Sensing and Learning In Structured Non-stationary Environments
    (2024-01) Gao, Jing
    In large infrastructure systems, sensing is key to maintain high quality information for decision making, while sometimes the non-stationary nature of the systems and short-lived agents in the systems make it hard to merge exploration and exploitation. One way to overcome such difficulty is to explore the resources in the system and information can be shared with all decision makers, in my dissertation, we’ll take the national airline as the examples to study the structured non-stationary environments. Aircraft in the National Aviation System (NAS) often rely on wind information from the National Oceanic and Atmospheric Administration (NOAA) to calculate favorable paths. However, wind conditions are dynamic and the NOAA information becomes quickly outdated because it is based upon sparse sampling both in space and time. This leads to inefficient, slower, paths used in practice. A goal of the Federal Aviation Administration’s (FAA) NextGen program is to use dynamic information to reduce inefficiencies. One such way to obtain high quality dynamic information and reduce inefficiency is to use en-route aircraft as ‘sensors’. This raises a natural question, “if a fraction of the aircraft can be used for sampling, how should aircraft be routed to provide most useful information for other aircraft to minimize system costs?” To answer this question, we begin with a stylized model of the aircraft routing problem, and capture the uniquely spatial and temporal correlations in wind dynamics. In Chapter 2, we analyzed the travel time at a paths' level, by modeling spatial and temporal correlation between the travel time along different paths, and formulating the travel time as a Brownian surface. Under this uncertainty structure, we address two questions: (i) if an offline schedule of paths to be sampled is desired, what is the optimal sampling schedule? and (ii) if the paths to be sampled are to be chosen in real time according to flight schedules, what is a near-optimal sampling policy? We provide answers to these questions using state-independent policies and state-dependent policies with provable guarantees in Chapter 3. In Chapter 4, we generate a comprehensive testbed from real-world flight data and computationally evaluate the performance of our sampling policies. Our testbed consists of seventeen origin-destination airport pairs, with five short-haul, seven medium-haul and five long-haul pairs. Our results show that collecting the right information and utilizing it to plan future aircraft routes could reduce a flight's travel time and associated fuel burn by 5% on average. Our modeling framework and results are also applicable to smaller, intra-city aircraft and unmanned aircraft such as UAVs and drones. The promising results and discoveries inspire us to delve deeper into the realm of bandit problems in structured non-stationary environments. After thoroughly surveying and summarizing the existing work, in Chapter 5, we extend the non-stationary structures to the combinatorial settings. This expansion allows us to examine how the intersection of links affects the common arcs in airline networks. Our goal is to explore the impact of link intersections on paths that share common arcs and to propose a near-optimal policy for this scenario. We approach this investigation from two directions, each offering potential solutions. We conclude in Chapter 5 with the discussion of the ongoing jobs and promising future research directions.
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    Silicon Waveguide Integrated Nanoplasmonics for Optoelectronic and Sensing Applications
    (2018-08) Chen, Che
    Silicon photonics, utilizing silicon and other semiconductors for on-chip light manipulation, has scaled the conventional optoelectronic devices (e.g. waveguide, photodetector and modulators) down to sub-micrometer footprint. This enables rack-to-rack high-bandwidth optical communication in data centers. Moreover, silicon photonics provides an on-chip platform for fundamental research including optomechanics, cavity electrodynamics and chemical sensing. On the other hand, surface plasmon polariton (SPP), can confine light into hotspot below optical diffraction limit and significantly enhance local electromagnetic field. This boosts the light-matter interaction significantly and enable biosensing applications including SERS and SEIRA. However, the metallic structure introduces high optical absorption, which is detrimental for long distance light propagation. In this dissertation, we focus on the on-chip integration of silicon photonics and plasmonics: using the dielectric waveguide for light delivery and plasmonics for light focusing. This integration approach combines the advantages of the low propagation loss of silicon waveguides, high-field confinement of a plasmonic structure for enhanced light-matter interaction. In the first project, we show the integration of a black phosphorus photodetector in a three-dimensional architecture of silicon photonics and metallic nanoplasmonics structures. By vertically integrating plasmonic grating on top of a silicon waveguide grating, a nanoscale optic hotspot is created. Adding another layer of 2D material, black phosphorus, an efficient telecom-band photodetector is fabricated. The short-channel (∼60 nm) BP FET shows an on-off ratio up to 1000. Moreover, benefiting from the ultrashort channel and near-field enhancement enabled by the nanogap structure, the photodetector shows an intrinsic responsivity as high as 10 A/W afforded by internal gain mechanisms, and a 3-dB roll-off frequency of 150 MHz. Such a hybrid integration also obviates the need for a bulky free-space optics setup and can lead to fully integrated, on-chip optical sensing systems. In the second project, we directly pattern an ultra-compact plasmonic resonator atop a mid-infrared silicon waveguide for spectroscopic chemical sensing. The footprint of the plasmonic nanorod resonators is as small as 2 µm2, yet they can couple with the mid-infrared waveguide mode efficiently. The plasmonic resonance is verified by measuring the transmission spectrum of the waveguide, with a coupling efficiency greater than 70% and a field intensity enhancement factor of over 3600 relative to the evanescent waveguide field intensity. Using this hybrid device and a tunable mid-infrared laser source, surface-enhanced infrared absorption spectroscopy of both a thin PMMA film and an octadecanethiol monolayer are successfully demonstrated.
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    A Single-Element Fiber Transducer for All-Optical Ultrasound and Photoacoustic Sensing
    (2019-12) Vilanguppam Thathachary, Supriya
    The past few decades have seen a rapid rise in minimally invasive medical procedures performed around the globe. These procedures have been made possible largely because of innovations in medical imaging and sensing to guide physicians in performing the interventions safely. Ultrasound technology has remained highly popular through this transition due to its safety and efficacy. However, the demand for miniature flexible devices for increased accessibility has prompted a shift toward all-optical ultrasound devices. Additionally, photoacoustic imaging and sensing have emerged as a promising technology with abilities to enhance diagnostic capabilities in several clinical applications, most significantly in the imaging of atherosclerotic plaque. The Fabry-perot ultrasound detector, being one of the more widespread optical ultrasound detection technologies, has been explored significantly in this context. This thesis presents a novel wave-guided configuration for fiber Fabry-Perot ultrasound detectors. This work demonstrates 16 times higher sensitivity than traditional piezoelelectric technology at comparable size scales. The chapters that follow present the simulations and experiments conducted around (a) optimizing the fabrication of the wave-guided fiber Fabry-Perot devices, (b) the complete optical and acoustic characterization of the fabricated devices, and (c) the potential improvements that can be made with incorporating dielectric mirrors. The thesis concludes with a discussion on the possible configurations for creating a complete ultrasound and photoacoustic probe for guiding minimally invasive interventions.