Theses and Dissertations from UMD
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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 give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Wide Field of View Spectroscopy Using Fabry-Perot Interferometers(2016) Nikoleyczik, Jonathan Allen; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We present a high resolution spectrometer consisting of dual solid Fabry-Perot Interferometers (FPIs). This work is intended to be an all inclusive documentation of the instrument including discussion of the design of this instrument, the methods used in data reduction, and the analysis of these data. Each FPI is made of a single piece of L-BBH2 glass which has a high index of refraction n~2.07 with a thickness on the order of 100 μm. Each is then coated with partially reflective mirrors to create a resonant cavity and thus achieve a spectral resolution of R~30,000. Running the FPIs in tandem reduces the overlapping orders and allows for a much wider free spectral range and higher contrast. We will also discuss the properties of the FPIs which we have measured. This includes the tuning of the FPIs which is achieved by adjusting the temperature and thus changing the FPI gap and the refractive index of the material. The spectrometer then moves spatially in order to get spectral information at every point in the field of view. We select spectral lines for further analysis and create maps of the line depths across the field. Using this technique we are able to measure the fluorescence of chlorophyll in plants and attempt to observe zodiacal light. In the chlorophyll analysis we are able to detect chlorophyll fluorescence using the line depth in a plant using the sky as a reference solar spectrum. This instrument has possible applications in either a cubesat or aerial observations to measure bulk plant activity over large areas.Item Polymer Based Miniature Fabry-Perot Pressure Sensors with Temperature Compensation: Modeling, Fabrication, and Experimental studies(2013) Bae, Hyungdae; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Miniature Fabry-Perot (FP) pressure sensors have been of great interest because of their advantages of small sizes, high performance, and immunity to electromagnetic interference. Most of these sensors are built with silicon/silica materials that have good mechanical, chemical, and thermal stabilities. However, due to the large Young's modulus of silica/silicon, developing a high sensitivity miniature sensor becomes difficult. In addition, fabrication of these sensors often involves high temperature fusion bonding and harsh acid etching. On the other hand, a polymer material becomes an attractive choice for high sensitive and miniature pressure sensors due to its small Young's modulus relative to that of silicon/glass. Moreover, polymer processes can be performed under ambient pressure and temperature without hazardous chemicals. However, a polymer-based sensor suffers from high temperature sensitivity, which must be compensated to obtain accurate pressure measurements. In this dissertation, three types of polymer based FP miniature sensors for static or quasi-static pressure measurements are investigated through modeling, microfabrication, and experiments. First, co-axial and cross-axial FP sensors with a built-in fiber Bragg grating (FBG) for temperature measurement and compensation are studied. In both sensors, the FP cavity is precisely self-aligned with the optical axis by using the fiber as a natural mask, which eliminates the need for a photo mask and tedious optical alignments. Second, a FP sensor composed of a UV-molded optical cavity with a pre-written FBG is developed. For the first time, a UV molding process with an optical fiber based mold is developed for fabrication of miniature FP sensors. This process enables high accuracy optical alignment for UV molding. Taking advantage of the UV molding process, the third type of sensor features a hybrid dual FP cavity for simultaneous temperature and pressure measurements. A novel signal processing method is developed to retrieve the multiple cavity lengths with an improved speed, resolution, and noise resistance. Experimental studies show that these polymer based sensors have good pressure and temperature sensing performance as well as temperature compensation capabilities. In addition, blood pressure and intradiscal pressure measurements of a swine are performed, which demonstrates the feasibility of these sensors for biomedical applications.Item MINIATURE LOW-COHERENCE FIBER OPTIC ACOUSTIC SENSOR WITH THIN-FILM UV POLYMER DIAPHRAGM(2012) Stief, Felix; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A miniature low-coherence fiber optic acoustic sensor with a thin-film UV polymer diaphragm is developed and studied in this thesis to address the fundamental challenge of miniaturizing acoustic sensors. When miniaturizing an acoustic sensor, there is a critical size limitation at which the transduction mechanism deformation becomes too small for detection. However, a solution to this problem is to utilize a high resolution, low coherence fiber optic interferometric detection system coupled with a soft, thin-film transduction mechanism. A novel fabrication technique was developed to enable the use of elastomers, which inherently exhibit desirably low Young's modulus properties. In addition, the fabrication process enables fabrication of diaphragms at thicknesses on the order of nanometers. The fabrication process also renders highly tunable sensor performance and superior sensing quality at a low cost. The sensor developed exhibits a flat frequency response between 50 Hz and 4 kHz with a useable bandwidth up to 20 kHz, a dynamic range of 117.55 dB SPL, a signal to noise ratio (SNR) of 58 dB, and a sensitivity up to 1200 mV/Pa. In this thesis, it is further demonstrated that by using an array these sensors fabricated from the same batch facilitates accurate directional sound localization by utilizing the interaural phase difference (IPD) exhibited by sensor pairs. Future work is suggested to optimize the sensor performance for a specific application, to carry out studies of more complex array configurations, and to develop algorithms that can help increase the sound localization accuracy.