Mechanical Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2263
Browse
8 results
Search Results
Item Direct Laser Writing-Enabled Microstructures with Tailored Reflectivity for Optical Coherence Tomography Phantoms(2023) Fitzgerald, Declan Morgan; Sochol, Ryan D; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As the continuous push to improve medical imaging techniques produces increasingly complex systems, so too must the phantoms critical to the accurate evaluation of these systems evolve. The inclusion of precise geometries is a well documented gap in optical coherence tomography (OCT) phantoms, a gap felt more severely as the technology improves. This thesis seeks to investigate the feasibility of utilizing new manufacturing techniques in the production of OCT phantoms with complex geometries while developing a phantom to determine the sensitivity of OCT systems. The new manufacturing methods include the replication of microstructures printed via direct laser writing into PMMA photoresist, the tailored smoothing of surface roughness inherent to direct laser writing, and the selective retention of surface roughness in certain regions. Each of these methods were implemented in the manufacture of an OCT sensitivity phantom and were found to be effective in each of their respective goals.The efficacy of the sensitivity phantom in evaluating the minimum reflectance still detectable by an OCT system shows promise. Effective reflectivity ranging from 0 to ~1 was accomplished within a single angled element and should provide a basis for determining the minimum reflectivity that results in a signal-to-noise ratio of 1. Further improvements must be made to the phantom footprint and manufacturing before the phantom’s reliability is certain.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 ENHANCING THE COMBUSTION CHARACTERISTICS OF ENERGETIC NANOCOMPOSITES THROUGH CONTROLLED MICROSTRUCTURES(2018) Jacob, Rohit; Zachariah, Michael R; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Metastable Intermolecular Composites (MIC’s) are a relatively new class of reactive materials which, through the incorporation of nanoscale metallic fuel and oxidizer, have exhibited multiple orders of magnitude improvement in reactivity. Although considerable research has been undertaken, their reaction mechanism is still poorly understood, primarily due to the complex interplay between chemical, fluid mechanic and thermodynamic processes that happen rapidly at nanoscale. For my dissertation, I have attempted to tackle this problem by employing controlled nanomaterial synthesis routes and optical diagnostics to identify the dominant underlying mechanisms. I begin my investigation by examining the nature of metal nanoparticle combustion wherein, I employed laser ablation to generate size- controlled aggregates of titanium and zirconium nanoparticles and studied their combustion behavior in a hot oxidizing environment. The experiments revealed the dominant role of rapid nanoparticle coalescence, before significant reaction could occur, resulting in a drastic loss of nanostructure. The large-scale effects of sintering on MIC combustion was explored through a forensic analysis of reaction products. Electron microscopy was employed to evaluate the product particle size distributions and focused ion beam milling was used to expose the interior composition of the product particles. The experiments established the predominance of condensed phase reaction at nanoscale and the interior composition revealed the poor extent of reaction due to rapid reactant coalescence before attaining completion. In light of such limitations, the final part of my dissertation proposes a solution to counteract rapid, premature coalescence through the synthesis of smart nanocomposites containing gas generating (GG) polymers. The GG acts as a binder as well as a dispersant, which disintegrates the composite into smaller clusters prior to ignition, thereby avoiding large scale loss of nanostructure. High speed optical diagnostics including an emission spectrometer and a high-speed color camera pyrometer were developed to quantify the enhanced combustion characteristics which indicate an order of magnitude improvement in reactivity over counterparts using commercial nanomaterials. Moreover, thermal pretreatment as a possible bulk processing strategy to improve nanoaluminum reactivity in a MIC is examined, where a 1000% increase in reactivity was observed compared to the untreated case. Finally, composites of nanoaluminum and reactive fluoropolymers (PVDF) are examined as a possible candidate for energetic material additive manufacturing (EMAM) and its viability is demonstrated by 3D printing and characterizing reactive multilayer films.Item INVESTIGATION OF THERMO-OPTIC EFFECTS IN SILICON MICRORING RESONATORS FOR SENSING AND INTERROGATION(2017) Kim, Hyun-Tae; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Integrated photonics technology has great potential for enhancing the performance and reducing the volume and cost of optical sensing systems. Among many integrated photonic structures, silicon microring resonators have received much attention for both sensing and interrogation. Particularly, the high quality-factor of the microring resonators and the large thermo-optic coefficient and high thermal conductivity of silicon make them attractive for temperature sensing and thermally-tunable-filter-based interrogation. In this dissertation work, the thermo-optic effects in silicon microring resonators is studied and used in the silicon-ring-resonator-based temperature sensing and interrogation. The first objective of this dissertation work is to develop a highly sensitive photonic temperature sensor, which can be potentially used for achieving portable, compact temperature sensing systems employing a low-resolution on-chip spectrometer. However, the sensitivity of conventional silicon-ring-resonator-based temperature sensors is relatively low (less than ~80 pm/°C). These sensors often require the use of a bulky and expensive fine-resolution interrogator for high resolution temperature monitoring, since the sensor resolution is determined by the sensitivity. In this work, a novel photonic temperature sensor based on cascaded-ring-resonators with the Vernier effect is developed to simultaneously enhance the sensitivity and sensing range. With a proof-of-concept device, sensitivity enhancement of 6.3 times and sensing range enhancement of 5.3 times are demonstrated. On-chip optical interrogators employing a silicon-ring-resonator-based thermally tunable filter (SRRTF) offer a promising solution for realizing portable, compact optical sensing systems. However, the slow interrogation speed of conventional SRRTF-based interrogators (less than a few Hz) has hindered their application for dynamic sensing. The second objective of this dissertation work is to develop a high-speed SRRTF-based interrogator, which can be used to interrogate optical sensors monitoring dynamic parameters. In this work, an SRRTF-based system utilizing the nonlinear transient thermal response of the SRRTF is developed for the speed enhancement. High speed interrogation (100 kHz of interrogation speed) of a fiber Bragg grating (FBG) sensor is successfully demonstrated with this system. The third objective of the dissertation work is to further enhance the tuning speed and range of the previously developed SRRTF and to use it for simultaneous interrogation of multiplexed FBG sensors. Performance of SRRTF-based interrogators is primarily determined by thermal and optical characteristics of the SRRTF. However, conventional SRRTF structures with a metallic heater on the top oxide cladding have limitations on interrogation speed and range. In this dissertation work, a novel SRRTF employing an interior-ridge-ring resonator and thermal through-cladding-vias is developed, which can realize enhanced tuning speed and range. With this SRRTF, interrogation of multiplexed FBG sensors at 125 kHz speed is demonstrated.Item Investigation of nanophotonic structures for imaging and sensing(2017) ZHANG, ZHIJIAN; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to image micro/nano scale objectives with miniaturized optical components has always been of great interest due to its great potential in applications such as microscopy, nanofabrication, and biomedical monitoring. However, in traditional practice using dielectric lenses, the focal size is inevitably limited by the Abbe’s diffraction limit (0.51fλ/ρ). Here, λ is the wavelength in vacuum, and f and ρ are the focal length and the radius of the lens, respectively. Moreover, the performance of conventional spherical lenses deteriorates as their sizes approach the wavelength. On the other hand, owing to the recent advances in micro/nano fabrication techniques, miniature sensors have received much attention, which are highly desirable in many sensing applications for physical, chemical, and biomedical parameter measurements. However, the performance of miniature sensors usually suffers from the similar difficulty as miniaturized imaging systems. Recently nanophotonic structures have been explored for the development of miniaturizing imaging and sensing systems due to their capability of confining and manipulating light at a subwavelength scale. In this dissertation work, several different mechanisms that nanophotonic structures can be used to help enhance the performance of imaging and sensing in miniaturized systems are investigated. First, plasmonic lens utilizing the nanophotonic structure to achieve the subwavelength focusing ability is studied. Three different regions in the plasmonic lens design are defined. Furthermore, a plasmonic lens in the Fresnel’s region is designed and k.ed to achieve a sub-diffraction limit focus. Second, radially polarized light generated by the TEM mode in the annular aperture in metal is investigated, which can further enhance the focusing ability. Third, in terms of sensing, an ultra-thin plasmonic interferometer constructed with a nano-hole array is fabricated on a fiber facet. By using this structure, the multi-parameter sensing capability of this interferometer is demonstrated; high sensitivity refractive index and temperature sensing are achieved. Finally, a novel sensor design based on the cladding modes and buffer modes generated by the planar grating on the fiber facet is proposed. Experimental studies of this sensor demonstrate its superior temperature sensitivity and the potential of multi-parameter sensing.Item PRINCIPLES FOR NEW OPTICAL TECHNIQUES IN MEDICAL DIAGNOSTICS FOR mHEALTH APPLICATIONS(2014) Balsam, Joshua; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Medical diagnostics is a critical element of effective medical treatment. However, many modern and emerging diagnostic technologies are not affordable or compatible with the needs and conditions found in low-income and middle-income countries and regions. Resource-poor areas require low-cost, robust, easy-to-use, and portable diagnostics devices compatible with telemedicine (i.e. mHealth) that can be adapted to meet diverse medical needs. Many suitable devices will need to be based on optical technologies, which are used for many types of biological analyses. This dissertation describes the fabrication and detection principles for several low-cost optical technologies for mHealth applications including: (1) a webcam based multi-wavelength fluorescence plate reader, (2) a lens-free optical detector used for the detection of Botulinum A neurotoxin activity, (3) a low cost micro-array reader that allows the performance of typical fluorescence based assays demonstrated for the detection of the toxin staphylococcal enterotoxin (SEB), and (4) a wide-field flow cytometer for high throughput detection of fluorescently labeled rare cells. This dissertation discusses how these technologies can be harnessed using readily available consumer electronics components such as webcams, cell phones, CCD cameras, LEDs, and laser diodes. There are challenges in developing devices with sufficient sensitivity and specificity, and approaches are presented to overcoming these challenges to create optical detectors that can serve as low cost medical diagnostics in resource-poor settings for mHealth.Item CAMERA SPECTRAL SENSITIVITY CHARACTERIZATION USING A BLACKBODY SOURCE(2011) Bedarkar, Rucha Sanjay; Sunderland, Peter B.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With digital cameras emerging as more effective tools for scientific research, there is increasing need for accurate and inexpensive ways to calibrate them. In particular, to date there has been no simple method to measure camera sensitivity as a function of wavelength. For example, narrow bandwidth monochromator beams are expensive and have calibration problems, while color chart method is unreliable owing to illumination dependence. This thesis presents a novel technique for spectral sensitivity calibration of a camera (or any black-and-white cameras or color sensors) using blackbody furnace operating at 650 - 1250 °C. Images recorded at 11 different temperatures are observed for red, green, and blue camera outputs. Using Planck ’ s Law to calculate the incident light intensities, the three color sensitivities as functions of wavelength are computed using MATLAB function that optimizes the spectral sensitivities until the blackbody measurements are closely matched. The results are in reasonable agreement with published sensitivities.Item Fiber Optical Tweezers for Microscale and Nanoscale Particle Manipulation and Force Sensing(2011) Liu, Yuxiang; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optical tweezers have been an important tool in biology and physics for studying single molecules and colloidal systems. Most of current optical tweezers are built with microscope objectives, which are: i) expensive, ii) bulky and hard to integrate, iii) sensitive to environmental fluctuations, iv) limited in terms of working distances from the substrate, and v) rigid with the requirements on the substrate (transparent substrate made with glass and with a fixed thickness). These limitations of objective-based optical tweezers prevent them from being miniaturized. Fiber optical tweezers can provide a solution for cost reduction and miniaturization, and these optical tweezers can be potentially used in microfluidic systems. However, the existing fiber optical tweezers have the following limitations: i) low trapping efficiency due to weakly focused beams, ii) lack of the ability to control the positions of multiple particles simultaneously, and iii) limited functionalities. The overall objective of this dissertation work is to further the fundamental understanding of fiber optical tweezers through experimental study and modeling, and to develop novel fiber optical tweezers systems to enhance the capability and functionalities of fiber optical tweezers as microscale and nanoscale manipulators/sensors. The contributions of this dissertation work are summarized as follows: i) An enhanced understanding of the inclined dual-fiber optical tweezers (DFOTs) system has been achieved. Stable three dimensional (3D) optical trapping of a single micron-sized particle has been experimentally demonstrated. This is the first time that the trapping efficiency has been calibrated and the stiffness of the trap has been obtained in the experiments, which has been carried out by using two methods: the drag force method and power spectrum analysis. Such calibration enables the system to be used as a picoNewton-level force sensor in addition to a particle manipulator. The influence of system parameters on the trapping performance has been carefully investigated through both experimental and numerical studies. ii) Multiple traps have been created and carefully studied with the inclined DFOTs for the first time. Three traps, one 3D trap and two 2D traps, have been experimentally created at different vertical levels with adjustable separations and positions. iii) Multiple functionalities have been achieved and studied for the first time with the inclined DFOTs. Particle separation, grouping, stacking, rod alignment, rod rotation, and optical binding have been experimentally demonstrated. The multiple functionalities allow the inclined DFOTs to find applications in the study of interaction forces in colloidal systems as well as parallel particle manipulation in drug delivery systems. iv) Far-field superfocusing effect has been investigated and successfully demonstrated with a fiber-based surface plasmonic (SP) lens for the first time. A planar SP lens with a set of concentric nanoscale rings on a fiber endface has been developed. For the first time, a focus size that is comparable to the smallest achievable focus size of high NA objective lenses has been achieved with the fiber-based SP lens. The fiber-based SP lens can bridge the nanoscale particles/systems and the macroscale power sources/detectors, which has been a long standing challenge for nanophotonics. In addition to optical trapping, the fiber-based SP lens will impact many applications including high-resolution lithography, high-resolution fluorescence detection, and sub-wavelength imaging. v) Trapping ability enhanced with the fiber-based SP lens has been successfully demonstrated. With the help of the fiber-based SP lens, the trapping efficiency of fiber optical tweezers has been significantly enhanced, which is comparable with that of objective-based optical tweezers. A submicron-sized bacterium has been successfully trapped in three dimensions for the first time with optical tweezers based on single fibers.