Browsing by Subject "sensor"
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Item A Broadband Miniaturized Microwave Dielectric Spectroscopy System Based on Impedance Sensing(2013-01-07) Kabiri, Saman 1988-The main purpose of this thesis is to propose a broadband miniaturized spectroscopy system to detect dielectric constant and loss tangent of lossy organic materials at RF/Microwave frequencies. Complex permittivities of lossy liquids are measured using voltage variations across a sensing element embedded in a capacitive divider circuit. The methodology for characterization of complex permittivity of materials is explained in detail. The proposed method provides a unique detection algorithm to extract the dielectric constant and loss tangent of an unknown material exposed to the sensor. The complex permittivity of binary organic mixtures have been extracted to an accuracy better than 5% using sample volumes of 200-300 ?L within the frequency range of 1-2 GHz. The results obtained from the measurements are compared to the reported values, and their agreements are presented in this work. To the best of the authors? knowledge, this is the first work presented for broadband miniaturized self-sustained complex permittivity spectroscopy at microwave frequencies.Item Airborne Infrared Target Tracking with the Nintendo Wii Remote Sensor(2012-11-12) Beckett, Andrew 1984-Intelligence, surveillance, and reconnaissance unmanned aircraft systems (UAS) are the most common variety of UAS in use today and provide invaluable capabilities to both the military and civil services. Keeping the sensors centered on a point of interest for an extended period of time is a demanding task requiring the full attention and cooperation of the UAS pilot and sensor operator. There is great interest in developing technologies which allow an operator to designate a target and allow the aircraft to automatically maneuver and track the designated target without operator intervention. Presently, the barriers to entry for developing these technologies are high: expertise in aircraft dynamics and control as well as in real- time motion video analysis is required and the cost of the systems required to flight test these technologies is prohibitive. However, if the research intent is purely to develop a vehicle maneuvering controller then it is possible to obviate the video analysis problem entirely. This research presents a solution to the target tracking problem which reliably provides automatic target detection and tracking with low expense and computational overhead by making use of the infrared sensor from a Nintendo Wii Remote Controller.Item Circular sensor array and nonlinear analysis of homopolar magnetic bearings(Texas A&M University, 2007-04-25) Wiesenborn, Robert KyleMagnetic bearings use variable attractive forces generated by electromagnetic control coils to support rotating shafts with low friction and no material wear while providing variable stiffness and damping. Rotor deflections are stabilized by position feedback control along two axes using non-contacting displacement sensors. These sensor signals contain sensor runout error which can be represented by a Fourier series composed of harmonics of the spin frequency. While many methods have been proposed to compensate for these runout harmonics, most are computationally intensive and can destabilize the feedback loop. One attractive alternative is to increase the number of displacement sensors and map individual probe voltages to the two independent control signals. This approach is implemented using a circular sensor array and single weighting gain matrix in the present work. Analysis and simulations show that this method eliminates runout harmonics from 2 to n-2 when all sensors in an ideal n-sensor array are operational. Sensor failures result in reduced synchronous amplitude and increased harmonic amplitudes after failure. These amplitudes are predicted using derived expressions and synchronous measurement error can be corrected using an adjustment factor for single failures. A prototype 8-sensor array shows substantial runout reduction and bandwidth and sensitivity comparable to commercial systems. Nonlinear behavior in homopolar magnetic bearings is caused primarily by the quadratic relationship between coil currents and magnetic support forces. Governing equations for a permanent magnet biased homopolar magnetic bearing are derived using magnetic circuit equations and linearized using voltage and position stiffness terms. Nonlinear hardening and softening spring behavior is achieved by varying proportional control gain and frequency response is determined for one case using numerical integration and a shooting algorithm. Maximum amplitudes and phase reversal for this nonlinear system occur at lower frequencies than the linearized system. Rotor oscillations exhibit amplitude jumps by cyclic fold bifurcations, creating a region of hysteresis where multiple stable equilibrium states exist. One of these equilibrium states contains subharmonic frequency components resulting in quasiperiodic rotor motion. This nonlinear analysis shows how nonlinear rotor oscillations can be avoided for a wide range of operation by careful selection of design parameters and operating conditions.Item Computational Study of the Development of Graphene Based Devices(2012-02-14) Bellido Sosa, EdsonGraphene is a promising material for many technological applications. To realize these applications, new fabrication techniques that allow precise control of the physical properties, as well as large scale integration between single devices are needed. In this work, a series of studies are performed in order to develop graphene based devices. First, using MD simulations we study the effects of irradiating graphene with a carbon ion atom at several positions and energies from 0.1 eV to 100 keV. The simulations show four types of processes adsorption, reflection, transmission, and vacancy formation. At energies below 10 eV the dominant process is reflection, between 10 and 100 eV is adsorption, and between 100 eV and 100 keV the dominant process is transmission. Vacancy formation is a low rate process that takes place at energies above 30 eV. Three types of defects were found: adatom, single vacancy, and 5-8-5 defect formed from a double vacancy defect. Also a bottom-up fabrication method is studied, in this method, the controlled folding of graphene structures, driven by molecular interactions with water nanodroplets, is analyzed considering the interactions with substrates such as SiO2, HMDS and IPA on SiO2. When the graphene is supported on SiO2, the attraction between graphene and the substrate prevents graphene from folding but if the substrate has HMDS or IPA, the interaction between graphene and the substrate is weak, and depending on the geometry of the graphene structure, folding is possible. Finally, to evaluate the characteristics of graphene based devices, we model the vibrational bending modes of graphene ribbons with different dimensions. The resonant frequencies of the ribbons and relations between the size of the ribbon and their resonant frequencies are calculated. The interaction of a graphene vibronic device with water and IPA molecules are simulated and demonstrate that this device can be used as a sensitive vibronic molecular sensor that is able to distinguish the chemical nature of the detected molecule. Also, the electrical properties of the graphene vibronic with armchair and zigzag border are calculated; the latter has the potential to generate THz electrical signals as demonstrated in this work.Item Design, simulation and analysis of a molecular nano-sensor operating at terahertz frequencies for energetic materials.(Texas A&M University, 2007-09-17) Shenoy, SukeshNano-sensors, as an application of nanotechnology, are extremely important for environmental, medical and security applications. Terahertz science is an exciting new field that is set to impact the field of sensing to a large extent. I proposed to combine the fields of nanotechnology and terahertz science and develop a molecular nano-sensor that operates at terahertz frequencies. I focused our sensing on energetic materials, particularly nitromethane, and conducted an extensive analysis on its frequency spectrum. The study also focused on designing the nano-sensor and determining its terahertz operation characteristics. I subjected it to various conditions through the use of molecular dynamics simulations. Finally we analyzed the simulation results and provided a proof of the concept that we had a working molecular nano-sensor that operates at terahertz frequencies and senses energetic materials. The results from the frequency analysis of nitromethane showed that the frequency characteristics determined from our simulations were in close agreement with the ones determined experimentally. In addition to this we also successfully demonstrated the use of a Lennard Jones potential to model the CN bond scission of nitromethane. Finally, the results from the interactions between the nano-sensor and nitromethane showed that the presence of nitromethane causes sufficient change in the terahertz frequency characteristics of the nano-sensor providing a means to detect nitromethane.Item Development of nano-scale and biomimetic surfaces for biomedical applications(Texas A&M University, 2006-10-30) Henry, James EdwardThe work described in this dissertation details the development of a biomimetic materials for use in sensors and therapeutics, based on new advances in material science. The sensors developed herein target neurodegenerative diseases. Two of the diseases, the transmissible spongiform encephalopathies (TSEs) and Alzheimer??????s disease (AD), are diseases associated with the abnormal folding of a protein, thus detecting the disease is dependent upon developing structure specific sensor technologies. Both sensors developed in this work take advantage of the unique optical properties associated with nanoscale metal particles, however they use different types of spectroscopies for optical detection of the presence of the disease associated abnormal protein, and different types of recognition elements that bring the disease associated proteins close to the nanoscale metal particles. In the case of TSEs, the recognition element was a commercially available antibody. In the case of AD, the recognition element was a molecular scale self-assembled surface. A therapeutic for AD was developed based on the molecular scale materials developed for the AD biosensor. Mathematical models were developed that facilitated the rational design of the biosensors described in this work that could also be used in future biosensor development.Item Fiber Fabry-Perot interferometer (FFPI) sensor using vertical cavity surface emitting laser (VCSEL)(Texas A&M University, 2006-10-30) Lee, Kyung-WooThis research represents the first effort to apply vertical cavity surface emitting lasers (VCSELs) to the monitoring of interferometric fiber optic sensors. Modulation of the drive current causes thermal tuning of the laser light frequency. Reflection of this frequency-modulated light from a fiber Fabry-Perot interferometer (FFPI) sensor produces fringe patterns which can be used to measure the optical path difference of the sensor. Spectral characteristics were measured for 850nm VCSELs to determine the combination of dc bias current, modulation current amplitude and modulation frequency for which single mode VCSEL operation and regular fringe patterns are achieved. The response characteristics of FFPI sensors were determined experimentally for square, triangular, saw-tooth waveforms at frequencies from 10kHz to 100kHz. The dependence of VCSEL frequency on the dc bias current was determined from spectral measurements to be ~165GHz/mA. An independent measurement of this quantity based on counting fringes from the FFPI sensor as the laser modulated was in good agreement with this value. The effect of optical feedback into the laser was also studied. By observing the fringe shift as the FFPI sensor was heated, a fractional change in optical length with temperature of 6.95 X 10-6/????C was determined in good agreement with previous measurements on a 1300nm single mode fiber. The performance of 850nm VCSEL/FFPI systems was compared with their counterparts using 1300nm distributed feedback (DFB) lasers. The results of these experiments show that the 850nm VCSEL/FFPI combination gives regular fringe patterns at much lower bias current and modulating current amplitudes than their 1300nm DFB/FFPI counterparts.Item Integration of functional components into microfluidic chemical systems: bioimmobilization and electrochemiluminescent detection on-chip(Texas A&M University, 2005-08-29) Zhan, WeiWe have investigated and implemented several general strategies in the development of microfluidics-based chemical/biochemical sensing systems. The research in this dissertation covers the immobilization of biological reagents inside microfluidic channels using polystyrene (PS) microbeads and photopolymerizable hydrogel, electrochemical sensing via electrochemiluminescence (ECL) reporting with bipolar and two-electrode configurations, and integration of these general functions to realize multiplexing and networking on-chip. Photopolymerizable hydrogel based on Poly(ethylene glycol) (PEG) and streptavidin-coated polystyrene (PS) microbeads were employed as building blocks as well as functional components in microfluidic system. PEG hydrogels can be used to define local microenvironments at different locations in the same microchannel, which enables the introduction of multiple sensing events on the same device. Monitoring of DNA hybridization and enzyme/substrate interaction were realized thereafter by using either fluorescence or electrochemistry as the detection method. Electrogenerated chemiluminescence based on Ru(bpy)32+ (bpy = 2,2??-bipyridine) and tripropylamine (TPA) was used to photonically report various redox events in microfluidic systems. By using microfluidic electrochemical cells based on either two-electrode or bipolar electrode (one-electrode), electroactive species that undergo reduction can be electrically linked to this anodic ECL process and thus be reported by the latter. This ECL sensing scheme essentially broadens the spectrum of redox compounds that can be detected by ECL since the analytes are not required to directly participate into the light-generating processes. Microfluidics offers some unique technical advantages of performing electrochemistry over conventional methods. In particular, laminar flow allows multiple analyte streams to be brought together in parallel with little mixing. Moreover, electrochemical signals can be generally utilized as a convenient means to link individual microchannels together hence to realize microfluidic networking and cross-communication. Electrochemical microfluidic devices can be used to mimic general functions of microelectronic devices such as diodes, transistors, and logic gates. These novel functions rendered by electrochemistry are believed to bring us closer to the final goals of micro total analysis systems and lab-on-a-chip.Item Optical Perfusion and Oxygenation Characterization in a Liver Phantom(2012-02-14) King, Travis J.Continuous monitoring of blood perfusion and oxygenation is essential in assessing the health of a transplanted organ. Particularly, monitoring the perfusion and oxygenation of the organ during the two-week period after the transplant procedure is crucial in detecting a sustained loss in perfusion or a reduction in oxygen saturation before these changes render irreversible damage to the organ or patient. Pulse oximetry is a clinically accepted method of monitoring the arterial oxygen saturation of a patient in a non-invasive manner. Pulse oximeters exploit the wavelength-dependent absorption of oxygenated and deoxygenated hemoglobin to measure a patient's arterial oxygen saturation. However, traditional pulse oximeters do not provide perfusion information and produce erroneous oxygen saturation measurements under low perfusion levels. An optical blood perfusion and oxygenation sensor, based on a modified reflectance pulse oximeter, has been developed for in situ monitoring of transplanted organs. To reduce the number of animal experiments, phantoms that mimic the optical and anatomical properties of liver parenchyma have also been developed. In this work, in vitro data was gathered from dye solutions mimicking oxygenated blood that were pumped through single and multi-layer phantoms mimicking liver parenchyma and through a phantom mimicking the portal vein. A portion of the phantom data was compared to data collected from in vivo occlusion studies performed on female swine to assess the ability of the phantoms to mimic the response observed with changes in blood perfusion through liver parenchyma. Both the single layer and multilayer phantoms showed a similar response to changes in perfusion as the in vivo case. With each phantom, the signal increased linearly with increases in perfusion, but the multilayer phantom showed a higher sensitivity (approximately 30% higher) to changes in perfusion than the single layer phantom. This higher sensitivity would provide the ability to measure smaller changes in perfusion and increase the resolution of the sensor. Also, both parenchymal phantoms showed similar trends in the oxygenation studies, with the R value decreasing with increasing oxygenation. While the observations in this research demonstrate the ability to use both phantoms for in vitro experiments, the results show the multilayer phantom is a better option for mimicking perfusion because it displays similar occlusion patterns as the liver parenchyma in vivo, a higher sensitivity to changes in perfusion than the single layer phantom, and it is only slightly more complex in design (contains only two more layers of sinusoids) than the single layer phantom.Item Performance and application of the Modular Acoustic Velocity Sensor (M.A.V.S.) current meter for laboratory measurements(Texas A&M University, 2005-02-17) Besnard, StephaneEvery type of current meter is different and has its proper characteristics. Knowing the performance of a current meter is essential in order to use it properly either for field or laboratory measurements (such as in the Offshore Technology Research Center wave basin). A study of the MAVS (Modular Acoustic Velocity Sensor) in a wave basin is a first step essential for later deployment in real studies. This thesis is based on data obtained from different series of laboratory measurements conducted in the OTRC wave basin. The objective of the first part of the study was to characterize the MAVS frequency response using benchmarks such as tow tests or wave tests. These benchmarks allowed us not only to characterize the sensor but also to eventually correct some of the measurement distortions due to flow blockage, vortex shedding, or vibrations of the mounting structure, for example. After the preliminary study was done, we focused on the potential use of the MAVS in the OTRC wave basin. Indeed, in the case of a study of a scale model in the wave basin, the stresses applied to the model have to be accurately known. In the case of current-induced loads, this includes contributions from both the mean flow and the turbulence. Thus, after correcting the values measured by the MAVS, a mapping of the current jet was executed to determine its three-dimensional structure in the wave basin. Knowing the structure of the current in the OTRC wave basin, it was then possible to define a domain in which the current can be considered uniform with a certain tolerable error. This domain of uniformity will allow us to validate the use of the OTRC wave basin to study large models such as FPSOs (Floating Production, Storage and Offloading Units).Item Simulation and Optimization of Wind Farm Operations under Stochastic Conditions(2011-08-08) Byon, EunshinThis dissertation develops a new methodology and associated solution tools to achieve optimal operations and maintenance strategies for wind turbines, helping reduce operational costs and enhance the marketability of wind generation. The integrated framework proposed includes two optimization models for enabling decision support capability, and one discrete event-based simulation model that characterizes the dynamic operations of wind power systems. The problems in the optimization models are formulated as a partially observed Markov decision process to determine an optimal action based on a wind turbine's health status and the stochastic weather conditions. The rst optimization model uses homogeneous parameters with an assumption of stationary weather characteristics over the decision horizon. We derive a set of closed-form expressions for the optimal policy and explore the policy's monotonicity. The second model allows time-varying weather conditions and other practical aspects. Consequently, the resulting strategy are season-dependent. The model is solved using a backward dynamic programming method. The bene ts of the optimal policy are highlighted via a case study that is based upon eld data from the literature and industry. We nd that the optimal policy provides options for cost-e ective actions, because it can be adapted to a variety of operating conditions. Our discrete event-based simulation model incorporates critical components, such as a wind turbine degradation model, power generation model, wind speed model, and maintenance model. We provide practical insights gained by examining di erent maintenance strategies. To the best of our knowledge, our simulation model is the rst discrete-event simulation model for wind farm operations. Last, we present the integration framework, which incorporates the optimization results in the simulation model. Preliminary results reveal that the integrated model has the potential to provide practical guidelines that can reduce the operation costs as well as enhance the marketability of wind energy.