UMD Theses and Dissertations
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item DESIGN OF A LOW-COST PORTABLE HANDHELD SPECTROMETER FOR AEROSOL OPTICAL DEPTH MEASUREMENTS(2022) LaRosa, Anthony; Yu, Miao MY; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The impact aerosols have on human health and the climate continues to be a central topic in scientific research. The quantification of aerosol abundance in the atmosphere is a key factor in understanding the climate, Earth’s radiative budget, and their impacts to human health. This research focuses on the development and comprehensive assessment of a handheld field instrument that measures aerosol optical thickness. The challenges associated with designing a low-cost, durable handheld system with highly sensitive electronics, which is capable of direct-sun measurements, are investigated. The thesis work can be summarized as follows. First, the electrical, mechanical, and optical integration needed for the instrument development is discussed and presented. Second, the sensitivities of a compact micro spectrometer are analyzed in both the laboratory and field deployment studies. The spectrometer and the fully integrated instrument are characterized in terms of its spectral resolution, sensitivity, thermal characteristics, and stability. Finally, after successful performance characterization, the capabilities of the instrument for field measurements are explored by taking direct sun measurements. The results demonstrate that the instrument has great potential to be used as a rigorous scientific device or a citizen science, educational instrument for aerosol optical depth measurements.Item SEMICONDUCTOR AND GLASS MICRO-RESONATORS(2015) KUO, LICHIANG; Davis, Christopher; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis we have demonstrated the cascading of two photonic AND logic gates by using two symmetric semiconductor GaAs microring resonators. In addition, we have developed a new, low-cost method for fabricating glass microring resonators. In the first part of this work, we discuss the properties of microring resonators and describe the fabrication of semiconductor microring resonators by the research team of which I was a member. In the experiments on cascaded logic gates we launched one probe and pump beam into different input waveguides, respectively. The first ring works as a AND logic gate for probe and pump beams. The output beam from the first ring goes to the second ring. The second ring also work as a AND logic gate using the second pump to switch the beam coming from the first ring. We successfully demonstrated cascading two photonic logic gates by using two symmetric semiconductor GaAs microrings. In the second part of this work, we extended our prior work on the fabrication of semiconductor microrings in a clean room to a purely mechanical method of glass microring fabrication. Many laboratories, including ours, lack the expensive facilities needed for the lithographic fabrication of microrings. And, a low-cost, high yield method of fabrication may have significant application in the development of disposable microring sensors. We have built up a complete mass=production capability based on glass capillary pulling and micro-polishing to fabricate glass microrings, because there were no available off-the-shelf systems available from industry at affordable prices. This method of producing highly polished glass micro-resonators has many advantages, such as fast fabrication (≦6 weeks), high yield (≧50%) (percentage of devices w/o cracks on edge), low cost (no need to use costly facilities in a clean room), mass production (800~1200 devices per batch). The surface quality of glass resonators should be excellent because capillaries were made at high temperature ≧1000℃ and devices were polished by suspension slurry of 70 nm colloidal silica. Further measurements that are beyond our current capability are needed for final verification. If some fabrication steps could be optimized in the future, we estimate that the fabrication time could be within 2 weeks, the yield rate would be higher than 90 %, and the number of devices per batch could be more than 1,200. This innovative method opens a new path for microresonator fabrication at low cost and in fast mass production. In sensor applications where low cost and mass production could be important, our work is an important first step to making microring sensors inexpensive, if further work in characterizing them can be done. Glass microresonators can play a key role, for example, in gas sensors, chemical sensors, liquid sensors, biological sensors, and vibration sensors. Two appendices in this thesis list the most significant sub-systems of the whole system we designed and built for producing glass microring resonators. Designs and engineering drawings are also listed in Appendices.Item Understanding and Mimicking the Fly's Directional Hearing: Modeling, Sensor Development, and Experimental Studies(2012) Liu, Haijun; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microphone arrays have been widely used in sound source localization for many applications. In order to locate the sound in a discernible manner, the separation between microphones needs to be greater than a critical distance, which poses a fundamental constraint for the miniaturization of directional microphones. In nature, animal hearing organs are also governed by the size constraint; the smaller the organ size, the smaller the available directional cues for directional hearing. However, with an auditory organ separation of only 520 µm, the fly Ormia ochracea is found to exhibit remarkable ability to pinpoint its host cricket at 5 kHz. The key to this fly's phenomenal directional hearing ability is believed to be the mechanical coupling between the eardrums. This innovative solution can inspire one to find alternative approaches to tackle the challenge of developing miniature directional microphones. The overall goal of this dissertation work is to unravel the underlying physics of the fly ear hearing mechanisms, and to apply this understanding to develop and study novel bio-inspired miniature directional microphones. First, through mechanics and optimization analysis, a fundamental biological conclusion is reached: the fly ear can be viewed as a nature-designed optimal structure that is endowed with the dual optimality characteristic of maximum average directional sensitivity and minimum nonlinearity, at its working frequency of 5 kHz. It is shown that this dual optimality characteristic is only achievable when the right mechanical coupling between the eardrums is used (i.e., proper contributions from both rocking and bending modes are used). More importantly, it is further revealed that the dual optimality characteristic of the fly ear is replicable in a synthetic device, whose structural parameters can be tailored to work at any chosen frequency. Next, a novel bio-inspired directional microphone with mechanically coupled diaphragms is designed to capture the essential dynamics of the fly ear. To study the performance of this design, a novel continuum mechanics model is developed, which features two coupling modules, one for the mechanical coupling of the two diaphragms through a beam and the other for each diaphragm coupled through an air gap. Parametric studies are carried out to explore how the key normalized parameters affect the performance of this directional microphone. Finally, this mechanics model is used to guide the development of a large-scale microphone and a fly-ear sized microphone, both of which are experimentally studied by using a low-coherence fiber optic interferometric detection system. With the large-scale sensor, the importance of using proper contribution from both rocking and bending modes is validated. The fly-ear sized sensor is demonstrated to achieve the dual optimality characteristic at 8 kHz with a ten-fold amplification in the directional sensitivity, which is equivalent to that obtainable from a conventional microphone pair that is ten times larger in size. To best use this sensor for sound source localization, a robotic platform with a control scheme inspired by the fly's localization/lateralization scheme is developed, with which a localization accuracy of better than ±2 degrees (the same as the fly ear) is demonstrated in an indoor lab environment. This dissertation work provides a quantitative and mechanistic explanation for the fly's sound localization ability for the first time, and it provides a framework for the development of fly-ear inspired acoustic sensors that will impact many fronts.Item Authentication of Fingerprint Scanners(2012) Ivanov, Vladimir Iankov; Baras, John S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To counter certain security threats in biometric authentication systems, particularly in portable devices (e.g., phones and laptops), we have developed a technology for automated authentication of fingerprint scanners of exactly the same type, manufacturer, and model. The technology uses unique, persistent, and unalterable characteristics of the fingerprint scanners to detect attacks on the scanners, such as detecting an image containing the fingerprint pattern of the legitimate user and acquired with the authentic fingerprint scanner replaced by another image that still contains the fingerprint pattern of the legitimate user but has been acquired with another, unauthentic fingerprint scanner. The technology uses the conventional authentication steps of enrolment and verification, each of which can be implemented in a portable device, a desktop, or a remote server. The technology is extremely accurate, computationally efficient, robust in a wide range of conditions, does not require any hardware modifications, and can be added (as a software add-on) to systems already manufactured and placed into service. We have also implemented the technology in a demonstration prototype for both area and swipe scanners.Item Oxygen Measurement During Cell Culture: From Multiwell Plates to Microfluidic Devices(2011) Thomas, Peter Chung; Forry, Samuel P; Raghavan, Srinivasa R; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Oxygen is an important regulator of normal cell behavior. Proper supply of oxygen is required to maintain ATP production, while perturbation of oxygen supply alters cell behavior and leads to tissue damage and cell death. In vivo, cells are exposed to a mean partial pressure of oxygen between 0.03 to 0.09 atm that is tissue specific. In contrast, conventional cell cultures are routinely performed at an atmospheric oxygen level of 0.21 atm. The disparity between in vivo and in vitro oxygen levels have been shown to affect cell viability, growth and differentiation. Continuous measurements and control of oxygen levels are thus critical to maintaining proper cell behavior. Current methods of oxygen measurement are invasive, difficult to integrate with microscopy and lack imaging capabilities. To improve the current state of measurements, we have developed a new non-invasive oxygen sensor for in vitro cell culture. The sensor was prepared by incorporating a porphyrin dye, Pt(II) meso-Tetra(pentafluoro-phenyl)porphine (PtTFPP), into gas permeable poly(dimethylsiloxane) (PDMS) thin films. The response of the sensor to oxygen followed the linear Stern-Volmer equation and demonstrated an order of magnitude higher sensitivity compared to other sensors (KSV = 548 ± 71 atm-1). A multilayer design created by sandwiching the PtTFPP-PDMS with a thin film of Teflon AF followed by a second layer of PDMS effectively mitigated against cytotoxicity effects and provided a suitable substrate for cell attachment. To demonstrate the utility of the sensor, oxygen measurements were made continuously with NIH 3T3 mouse fibroblast cells. The oxygen levels were found to decrease as a result of oxygen consumption by the cells. Using Fick's law, the data was analyzed and a per-cell oxygen consumption rate for the 3T3 fibroblasts was calculated. In addition, cells were clearly visualized on the sensor demonstrating the ability to integrate with phase-contrast and fluorescence microscopy. Next, human hepatocellular carcinoma HepG2 were cultured on the oxygen sensor and continuous oxygen measurements showed a drastic decrease in oxygen level such that the cells were exposed to hypoxic conditions within 24 h. The per-cell oxygen consumption rate for HepG2 was determined to be 30 times higher than the 3T3 fibroblasts, confirming the high metabolic nature of these cells. At high densities, oxygen flux measurements showed an asymptotic behavior reaching the theoretical maximum of the culture condition. When the oxygen diffusion barrier was reduced, the oxygen flux increased, demonstrating insufficient oxygenation for HepG2 at these densities. In routine culture, HepG2 adhere to their neighboring cells which results in formation of cell clusters. Oxygen measurement confirmed the presence of oxygen gradient across the cell clusters with the lowest oxygen levels observed in the middle. Finally, we successfully integrated the oxygen sensor into microfluidic systems. The sensor provided real-time non-invasive measurements of oxygen levels on-chip. To regulate the oxygen levels in the device, water with different dissolved oxygen concentrations was used instead of gas. This method successfully mitigated the problems of pervaporation associated with previous devices. Physiologically relevant oxygen levels and oxygen gradients were easily generated on the device and the results showed excellent agreement with numerical simulations.Item POLYMER COMPOSITES FOR SENSING AND ACTUATION(2011) Kujawski, Mark Paul; Smela, Elisabeth; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis concerns materials for polymer actuators and mechanical sensors. Polymer actuators are a class of artificial muscle with promising actuation performance; however, they are currently limited by the materials used in their fabrication. The metal-foil type mechanical strain gauges are commercially available and well understood; however, typically have gauge factors less than 5.5 [1], cannot be patterned into custom shapes, and only monitor small areas. New materials provide opportunities to improve the performance of both polymer actuators and mechanical sensors. The aim of this research was to develop, characterize, and implement such materials. Specifically, this thesis describes novel composites of exfoliated graphite (EG) blended with elastomeric hosts. The mechanical and electrical properties of these composites were tailored for two specific applications by modifying the EG loading and the elastomer host: compliant electrodes and strain gauges. Compliant electrodes were demonstrated that had ultimate tensile strains greater than 300% and that could withstand more than 106 strain cycles. Composites fabricated with polydimethylsiloxane (PDMS) exhibited conductivities up to 0.2 S/cm, and having tangent moduli less than 1.4 MPa. This modulus is the lowest reported for loaded elastomers above the percolation threshold. Conductivity was increased to more than 12.5 S/cm by fabricating composites with polyisoprene (latex) elastomers, and the tangent moduli remained less than 5 MPa. Actuation strains of polymer actuators were increased 3 fold using the composites as electrodes, compared to using carbon-grease electrodes. This was due to the composites ability to be spincoated with thin insulating layers of PDMS, allowing 30% higher electric fields to be applied. Strain gauges fabricated with these composites exhibited gauge factors (GFs) > 27,000, to the authors knowledge this is the highest GF ever reported. The effects of humidity, temperature and strain were investigated.Item Microcantilever Biosensors with Chitosan for the Detection of Nucleic Acids and Dopamine(2007-05-07) Koev, Stephan; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microcantilever biosensors allow label-free detection of analytes within small sample volumes. They are, however, often limited in sensitivity or specificity due to the lack of proper bio-interface layers. This thesis presents the use of the biopolymer chitosan as a bio-interface material for microcantilevers with unique advantages. Sensors coated with chitosan were designed, fabricated, and functionalized to demonstrate two distinct applications: detection of DNA hybridization and detection of the neurotransmitter dopamine. The first demonstration resulted in signals from DNA hybridization that exceed by two orders of magnitude values previously published for sensors coated with SAM (self assembled monolayer) interface. The second application is the first reported demonstration of using microcantilevers for detection of the neurotransmitter dopamine, and it is enabled by chitosan's response to dopamine electrochemical oxidation. It was shown that this method can selectively detect dopamine from ascorbic acid, a chemical that interferes with dopamine detection in biological samples.