Browsing by Author "Dr. John Muth, Committee Chair"

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A 1 Mbps Underwater Communication System Using a 405 nm Laser Diode and Photomultiplier Tube
(2008-12-07) Cox, William Charles, Jr.; Dr. Brian Hughes, Committee Member; Dr. John Muth, Committee Chair; Dr. Robert Kolbas, Committee Member
Radio frequency communications in seawater are impractical due to high conductivity of seawater limiting the propagation of electromagnetic waves. Current methods, such as acoustic communication, are limited in bandwidth, and the use of cables, such as fiber optic, are expensive and not practical for autonomous vehicles. Underwater tethered communication systems are also very costly to repair if damaged. Optical wireless communications that exploit the blue/green transparency window of seawater potentially offer high bandwidth, although short range, communications. The goal of this Masters thesis was to build sufficient infrastructure to experimentally validate the performance of underwater optical communication systems under laboratory, but hopefully realistic, water conditions. An optical transmitter based on a 405nm blue laser diode was constructed. The transmitter is capable of sourcing 200mA of current to a blue laser diode at speeds of up to 200MHz. The receiver was based on a photomultiplier tube. The high gain and blue/green sensitivity of a photomultiplier tube make it ideal for underwater optical communications. Finally, a 1,200 gallon water tank was constructed that allows the water conditions to be appropriately controlled to simulate an ocean environment Experiments were conducted to validate the design and construction of the receiver, transmitter and water tank. An underwater optical data link was demonstrated that was capable of transmitting data at 500kpbs in return-to-zero format, or 1Mpbs in non-return-tozero format. The transmitted signal could then be optically detected, digitized and stored on a PC for later signal processing.
A Prototype Hadamard Imaging System
(2006-09-07) Fothergill, Daryl William; Dr. John Muth, Committee Chair; Dr. Robert Kolbas, Committee Member; Dr. David Lalush, Committee Member
The purpose of this thesis was to investigate the possibility of creating an inexpensive imaging system that would be suitable for imaging small animals, either the skin of mice for skin cancer studies, or potentially whole animal imaging. In this optical system the light is collected by an array of 31 optical fibers. In more advanced systems one can envision 1024, or even more fibers being used to increase the resolution of the image. The principle novelty of this system is that Hadamard encoding enabled only one photodetector to be used for the whole system rather than one detector for each fiber. There are two important advantages that can be obtained by using this strategy. First, especially with large numbers of fibers, the overall signal to noise ratio of the system can be improved. Second, the cost and complexity of the system can be greatly reduced. In cases where the signal to noise ratio is low, such as fluorescence detection, designing a system that has only one detector has substantial advantages. This system can also be applied to other sensor applications with large numbers of inputs. To our knowledge Hadamard imaging has not been applied to macroscopic imaging applications, or to small animal imagining. Plastic fiber optics are used to gather and pixilate the spatially dependent inputs from the light source. The optical fibers were then switched on and off using a rotating mask encoded with a Hadamard matrix by drilling holes in the mask. The encoded light was then detected with an inexpensive photodetector and decoded using a desktop computer. The system is automated by using a BASIC Stamp to control the stepper motors and LabVIEW. Future improvements such as a stationary MEMS mask and glass optical fibers that could improve the system by making it more efficient and smaller in size are discussed.