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Item Electrochmical impedance spectroscopy biosensor platform for evaluation of biofilm(Montana State University - Bozeman, College of Engineering, 2023) McGlennen, Matthew Connor Dusenbery; Co-chairs, Graduate Committee: Christine Foreman and Stephan Warnat; This is a manuscript style paper that includes co-authored chapters.Microbial biofilms are organized communities of surface-attached microorganisms encased in a self-produced extracellular matrix that pose significant challenges in medicine, the environment, and industry. Biofilms can cause chronic infections, biofouling, and equipment failure, while existing methods for biofilm detection are slow, costly, and labor-intensive. Recently, the use of microfabricated electrochemical impedance spectroscopy (EIS) biosensors has emerged as a promising technique for evaluating biofilm growth in real-time with advantages of small-size, adaptability, low-cost, and high-sensitivity. In this work, EIS biosensors featuring gold micro-interdigitated electrodes were produced using standard microfabrication techniques. Sensors were integrated into a custom 3D-printable flow cell system, enabling EIS measurements and confocal laser scanning microscopy (CLSM) imaging simultaneously. Green fluorescently labeled Pseudomonas aeruginosa PA01, a model biofilm forming bacteria, was introduced into flow chambers and subsequent growth was monitored by EIS, CLSM, and biomass enumeration. Using the system, biofilm growth, dispersal, and the effects of cell-signaling suppression were evaluated. The sensors were also tested in an oil-water emulsion and field-tested on an alpine snow-patch and pond. Improved stability of EIS measurements was achieved by coating the sensors' counter and reference electrodes with an electrically conductive polymer. Biofilm growth was successfully detected using EIS biosensors at an optimized single-frequency, with average decreases in impedance of ~22% by 24 hours. Likewise, biofilm dispersal via chemical treatments were successfully detected with average increases in impedance of ~14% over the ensuing 12 hours. When cells were exposed to a quorum sensing inhibition agent, impedance did not decrease for 18 hours. Impedance changes due to biofilm growth, dispersal, and effects of quorum sensing inhibition were validated by CLSM images and biofilm enumeration. Similarly, in an oil-water emulsion the biosensors successfully detected biofilm growth, dispersal, and effects of quorum sensing inhibition. In an alpine field-test, samples containing varying concentrations of microbes could be detected using the EIS biosensors. This work demonstrates that EIS biosensors are a promising tool for real-time monitoring of biofilm dynamics in a variety of aqueous environments. Overall, EIS biosensing holds great potential for in situ and real-time data regarding biofilm colonization that is not possible with existing techniques.Item The corrosion of mild steel : a new interpretation of ac impedance spectra of corroding mild steel(Montana State University - Bozeman, College of Letters & Science, 1995) Morrison, Michael LeeItem Electric terminal performance and characterization of solid oxide fuel cells and systems(Montana State University - Bozeman, College of Engineering, 2013) Lindahl, Peter Allan; Chairperson, Graduate Committee: Steven R. ShawSolid Oxide Fuel Cells (SOFCs) are electrochemical devices which can effect efficient, clean, and quiet conversion of chemical to electrical energy. In contrast to conventional electricity generation systems which feature multiple discrete energy conversion processes, SOFCs are direct energy conversion devices. That is, they feature a fully integrated chemical to electrical energy conversion process where the electric load demanded of the cell intrinsically drives the electrochemical reactions and associated processes internal to the cell. As a result, the cell's electric terminals provide a path for interaction between load side electric demand and the conversion side processes. The implication of this is twofold. First, the magnitude and dynamic characteristics of the electric load demanded of the cell can directly impact the long-term efficacy of the cell's chemical to electrical energy conversion. Second, the electric terminal response to dynamic loads can be exploited for monitoring the cell's conversion side processes and used in diagnostic analysis and degradation-mitigating control schemes. This dissertation presents a multi-tier investigation into this electric terminal based performance characterization of SOFCs through the development of novel test systems, analysis techniques and control schemes. First, a reference-based simulation system is introduced. This system scales up the electric terminal performance of a prototype SOFC system, e.g. a single fuel cell, to that of a full power-level stack. This allows realistic stack/load interaction studies while maintaining explicit ability for post-test analysis of the prototype system. Next, a time-domain least squares fitting method for electrochemical impedance spectroscopy (EIS) is developed for reduced-time monitoring of the electrochemical and physicochemical mechanics of the fuel cell through its electric terminals. The utility of the reference-based simulator and the EIS technique are demonstrated through their combined use in the performance testing of a hybrid-source power management (HSPM) system designed to allow in situ EIS monitoring of a stack under dynamic loading conditions. The results from the latter study suggest that an HSPM controller allows an opportunity for in-situ electric terminal monitoring and control-based mitigation of SOFC degradation. As such, an exploration of control-based SOFC degradation mitigation is presented and ideas for further work are suggested.Item In-situ electrical terminal characterization of fuel cell stacks(Montana State University - Bozeman, College of Engineering, 2010) Seger, Eric Matthew; Chairperson, Graduate Committee: Steven R. ShawThis thesis demonstrates in-situ characterization of a 5kW solid oxide fuel cell (SOFC) stack and a 165W proton exchange membrane fuel cell (PEMFC) stack at the electrical terminals, using impedance spectroscopy and time-domain modeling. The SOFC experiments are performed using excitation from the power electronic ripple current and exogenous excitation generated from several different sources including a hybrid system which uses a secondary power source for the generation of the small-signal currents. The PEMFC experiments are performed using exogenous excitation from a boost converter. In contrast to typical off-line analysis using specialized instrumentation, the measurements are made as the stacks deliver power to their respective loads. The power electronic switching waveform is used as a source of excitation. This technique could be implemented on-line for continuous condition assessment of the stack. The results show typical data from the stack, comparison of model predictions and measured data, and whole-stack impedance spectroscopy results.Item Synthesis and characterization of hydrogen separation membranes(Montana State University - Bozeman, College of Engineering, 2005) Lakshminarayanan, Karthikeyan; Chairperson, Graduate Committee: Vic A. CundyHydrogen can be obtained from purification of water gas by ceramic hydrogen separation membranes. These membranes need to be further improved to obtain reasonable production of hydrogen from water gas. Fuel cell materials and state of the art ceramic membranes were characterized by impedance spectroscopy and dielectric measurements. To block the ionic and electronic conductivity, blocking layers of MgO were used. The coating thickness was analyzed by RBS and SEM techniques. Dielectric measurements with blocking layers and impedance measurements without any blocking layers were made over a wide range of temperatures. The data obtained were used to model equivalent circuits. The activation energies and conductivities of the samples were also found from data obtained and were compared with those available in the literature. MgO was found to be a suitable blocking layer material.