CATRA: Interactive Measuring and Modeling of Cataracts

We introduce an interactive method to assess cataracts in the human eye by crafting an optical solution that measures the perceptual impact of forward scattering on the foveal region. Current solutions rely on highly-trained clinicians to check the back scattering in the crystallin lens and test their predictions on visual acuity tests. Close-range parallax barriers create collimated beams of light to scan through sub-apertures, scattering light as it strikes a cataract. User feedback generates maps for opacity, attenuation, contrast and sub-aperture point-spread functions. The goal is to allow a general audience to operate a portable high-contrast light-field display to gain a meaningful understanding of their own visual conditions. User evaluations and validation with modified camera optics are performed. Compiled data is used to reconstruct the individual's cataract-affected view, offering a novel approach for capturing information for screening, diagnostic, and clinical analysis.Alfred P. Sloan Foundation (Research Fellowship)United States. Defense Advanced Research Projects Agency (Young Faculty Award

Fabrication and Measurement of LT-GaAs Photoconductive Antennas and Arrays

This thesis presents the fabrication and measurement of LT-GaAs based terahertz (THz) photo conductive antennas (PCAs) and arrays. The LT-GaAs THz PCAs are fabricated to serve as reference devices to new 2D material black phosphorous (BP) based THz PCAs. The LT-GaAs and BP devices have identical metallic electrodes, allowing for a comparison of emitted THz intensity and bandwidth. All PCAs have been measured using an open bench pulsed time-domain spectroscopy (TDS) system with a usable bandwidth from 0.1-4 THz, pumped with a 780nm Ti:Sapphire femtosecond laser. The results have shown LT-GaAs devices outperforming BP devices in signal amplitude and bandwidth at identical DC bias voltages and pump powers. Three other electrode shape designs were achieved: circular, slotted, and fractal, fabricated on LT-GaAs. The effect of electrode shape on the amplitude and bandwidth of the THz pulse has been experimentally characterized. A comparison of all four shapes has shown that the bowtie electrodes provide a nominal increase in pulse amplitude under identical biasing conditions. Further, a polarization study using an x-cut quartz rotator was conducted, validating that all four electrode shapes are highly linearly polarized. Results show that the co-polarized THz pulse is two orders of magnitude greater than the cross-polarized THz pulse. In addition, two element THz PCAs with electrode spacings of 75µm, 150µm, and 300µm have been investigated. A novel feed network using two beam splitters has been designed, and implemented into the existing open bench TDS system. This feed network gives individual control over the position and path length of the beams feeding each elements. Further, a DC bias splitting PCB and switchboard were designed to allow each element to be turned on and off, aiding in laser alignment validation. The measurement of all three devices have shown the array THz pulse having a higher amplitude than either individual element, however, an insignificant effect on the array bandwidth has been observed

Fabrication and Measurement of LT-GaAs Photoconductive Antennas and Arrays

This thesis presents the fabrication and measurement of LT-GaAs based terahertz (THz) photo conductive antennas (PCAs) and arrays. The LT-GaAs THz PCAs are fabricated to serve as reference devices to new 2D material black phosphorous (BP) based THz PCAs. The LT-GaAs and BP devices have identical metallic electrodes, allowing for a comparison of emitted THz intensity and bandwidth. All PCAs have been measured using an open bench pulsed time-domain spectroscopy (TDS) system with a usable bandwidth from 0.1-4 THz, pumped with a 780nm Ti:Sapphire femtosecond laser. The results have shown LT-GaAs devices outperforming BP devices in signal amplitude and bandwidth at identical DC bias voltages and pump powers. Three other electrode shape designs were achieved: circular, slotted, and fractal, fabricated on LT-GaAs. The effect of electrode shape on the amplitude and bandwidth of the THz pulse has been experimentally characterized. A comparison of all four shapes has shown that the bowtie electrodes provide a nominal increase in pulse amplitude under identical biasing conditions. Further, a polarization study using an x-cut quartz rotator was conducted, validating that all four electrode shapes are highly linearly polarized. Results show that the co-polarized THz pulse is two orders of magnitude greater than the cross-polarized THz pulse. In addition, two element THz PCAs with electrode spacings of 75µm, 150µm, and 300µm have been investigated. A novel feed network using two beam splitters has been designed, and implemented into the existing open bench TDS system. This feed network gives individual control over the position and path length of the beams feeding each elements. Further, a DC bias splitting PCB and switchboard were designed to allow each element to be turned on and off, aiding in laser alignment validation. The measurement of all three devices have shown the array THz pulse having a higher amplitude than either individual element, however, an insignificant effect on the array bandwidth has been observed

Nondestructive Evaluation of Steel Bridges: Methods and Applications

Nondestructive evaluation (NDE) methods can be used to assess in-service steel bridges for problematic conditions caused by factors such as design, manufacturing, fabrication, and the service effects of traffic and corrosion. This report discusses typical NDE test methods used on bridges, including penetrant testing, magnetic particle testing, eddy current testing, ultrasonic testing (including phased array testing), radiography, and acoustic emission testing. NDE operations such as flaw location, characterization, and sizing are covered as well. Results of a national survey of departments of transportation’s (DOTs) use of NDE are presented. A simple procedure for using NDE to address DOT bridge concerns is proposed along with a risk-based inspection approach to scheduling/scoping bridge inspections

Improvement of oral reports through the students' use of audio-visual aids

Author misnumbered thesis. Please note that there are TWO page 108s, but the continuity is the same. Thesis (Ed.M.)--Boston Universit

Multispectral photography for earth resources

A guide for producing accurate multispectral results for earth resource applications is presented along with theoretical and analytical concepts of color and multispectral photography. Topics discussed include: capabilities and limitations of color and color infrared films; image color measurements; methods of relating ground phenomena to film density and color measurement; sensitometry; considerations in the selection of multispectral cameras and components; and mission planning

Computational and Experimental Approach for Non-destructive Testing by Laser Shearography

Non-destructive testing (NDT) is critical to many precision industries because it can provide important information about the structural health of critical components and systems. In addition, NDT can also identify situations that could potentially lead to critical failures. Specifically, NDT by optical methods have become popular because of their non-contact and non-invasive nature. Shearography is a high-resolution optical NDT method for identification and characterization of structural defects in components and has gained wide acceptance over the last decade. Traditional workflow of NDT by shearography has been determined to be inefficient, due to the requirements of having experienced operators that must determine the most suitable loading methods to identify defects in samples under testing as well as to determine the best system arrangement for obtaining the maximum measuring sensitivity. To reduce the number of experiments that are required and to allow inspectors to perform NDT by laser shearography in a more efficient way, it is necessary to optimize the experimental workflow. The goal of the optimization would be an appropriate selection of all experimental variables including loading methods, boundary conditions, and system¡¯s sensitivities, in order to avoid repeating experiments several times in the processes of components characterization and health monitoring. To achieve this goal, a hybrid approach using shearographic fringe prediction with Finite Element Analysis (FEA) has been developed. In the FEA simulations, different loading conditions are applied to samples with defects, and in turn, the shearographic fringes are predicted. Fringe patterns corresponding to specific loading conditions that are capable of detecting defects are chosen and experimental tests are performed using those loading conditions. As a result, using this approach, inspectors could try different combinations of loading methods, and system¡¯s sensitivities to investigate and select appropriate experimental parameters to improve defect detection capabilities of the system by using low-cost computer simulations instead of lengthy and expensive experiments. In addition, to improve the identification of defects on the sample, camera calibration and image registration algorithms are used to project the detected defects on the sample itself to locate and visualize the position of defects during shearographic investigations. This hybrid approach is illustrated by performing NDT of a plate made of acrylic that has a partial hole at the center. Fringe prediction with finite element analysis are used to characterize the optimized experimental procedures and in turn, corresponding measurements are performed. A multimedia projector is employed to project the defects on the surface of the plate in order to visualize the location of the partial hole (defect). Furthermore, shearographic system is used for other applications including NDT of a composites plate and of a thin latex membrane. The procedures shows the effectiveness of the approach to perform NDT with shearography methods

Detection of subsurface anomalies in fiber-reinforced polymer (FRP) wrapped timber bridge components using infrared thermography

This thesis presents the results of an experimental study on the use of Infrared Thermography technique for detection of subsurface anomalies in fiber reinforced polymer (FRP) wrapped timber bridge components. An extensive literature review on the application of various nondestructive evaluation techniques to composite structures has also been presented.;Simulated subsurface delaminations were constructed in the laboratory in timber piles wrapped with FRP composite fabric. The delaminations varied in size, thickness, and severity. These delaminations were placed between the 1/8&inches; thick FRP wrap and timber surface. The thermal images from the delaminated specimens were compared with thermal images from undamaged specimens to study the effect of subsurface anomalies. In addition, several field tests were conducted using the infrared imaging system on three timber railroad bridges located in Moorefield, West Virginia that were reinforced with FRP composite fabric. The field test data was used to detect debonds at the composite-timber interface and study the effect of environmental parameters on infrared images.;This study shows that the infrared thermography technique can be used to effectively to detect subsurface delaminations in timber components wrapped with FRP composite fabric. The study also shows the effect of different parameters (environmental conditions, heat source, etc.) on the clarity of infrared images

Volume 55 - Issue 6 - January, 1945

https://scholar.rose-hulman.edu/technic/1171/thumbnail.jp