Browsing by Author "Dr. Brian Hughes, Committee Member"

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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 1 Mbps Underwater Communications System using LEDs and Photodiodes with Signal Processing Capability
(2008-12-07) Simpson, Jim Anto; Dr. Brian Hughes, Committee Member; Dr. Leda Lunardi, Committee Member; Dr. John F. Muth, Committee Chair
The inability of radio frequency electromagnetic waves to propagate without attenuation in seawater has traditionally limited underwater communications to acoustics or tethered systems. High bandwidth optical communication systems have been demonstrated for terrestrial and space applications. There is growing interest to see if short range high bandwidth optical wireless systems can be made for the underwater environment. In this thesis we demonstrate a 1 Mbps optical wireless system using LEDs and PIN photodiodes that also incorporates capabilities for signal processing of the received data to be performed. Lasers and Photomultiplier tubes offer high performance, and are generally used in most underwater optical communication systems. However, these components are relatively expensive and can have large form factors. As an alternative solution the much cheaper and more compact LEDs and photodiodes are used as transmitters and receiver components. However, compared to a laser and PMT based system, such a system would be strongly disadvantaged in photon limited environments. If one assumes that photons actually reach the receiver, using signal processing techniques, optimized modulation formats, and error-correction coding, one expects that the range of the system can be extended. The development of a prototype system for the experimentation and verification of this proposition is the main motivation of this thesis. Small, compact transmitters using High Power LEDs and receivers using Si Photodiodes where the data can be digitally sampled such that signal processing techniques can be applied were constructed and demonstrated using a 12 foot, 1200 gallon tank that was also constructed for the project. It was shown that the LED and photodiode based system works well for short ranges, and that advantages can be obtained using digital signal processing. The applicability of this strategy to use digital signal processing techniques can be easily extended to higher performance Laser/PMT based systems.
Data fusion of multispectral remote sensing measurements using wavelet transform
(2003-04-02) Mehta, Viraj Kirankumar; Dr. Hamid Krim, Committee Chair; Dr. Marc Genton, Committee Member; Dr. Brian Hughes, Committee Member
This thesis focuses on fusion of multispectral data available from remote sensing instruments. The aim is to develop fast and memory efficient algorithms that may be used for real-time implementation aboard satellites. Multiple channel data from the SSM/I instrument are used for experiments. Starting with a Bayesian estimation formulation of the data fusion problem, an attempt is made to take advantage of the sparseness resulting from wavelet transforms to optimize computational efficiency. After generating the necessary statistical models for the data to be estimated, a preconditioning whitening filter, which simplifies the choice of the required wavelet transform, is developed. The significant gains obtained by a compact representation in wavelet basis are shown. An input grid transformation leading to channel filters is then used to construct a real-time implementation of the optimal estimator. Simulated results of such a system are then used to demonstrate the achieved improvement in field resolution. In conclusion, a direction for future work is laid out for improving the estimation optimality over non-stationarity by adaptive techniques and extension to future instruments.
Novel Compact Antennas for Biomedical Implants and Wireless Applications
(2005-08-09) Gosalia, Keyoor Chetan; Dr. Robert J. Trew, Committee Member; Dr. Zhilin Li, Committee Member; Dr. Gianluca Lazzi, Committee Chair; Dr. Brian Hughes, Committee Member
Novel design methodologies and implementation techniques for antennas with an extremely small form factor (kr < 1; k is the wavenumber and r is the radius of enclosing spherical volume) are presented. These size reduction techniques are applied to design antennas for two emerging fields: Short (or long) range wireless connectivity and human body implants (prosthetic devices). The first test bed describes compact microstrip patch antennas employing polarization diversity for optimizing the available channel bandwidth in conventional wireless communications. Extremely small antennas (for implantation in an eye ball) operating at microwave frequencies for a visual prosthesis are designed and implemented for the second test bed. The visual prosthesis under consideration is an implantable prosthetic device which attempts to restore partial vision in the blind (patients suffering from retinal degeneration) by artificial stimulation of the retinal cells. Mutually exclusive power and data transfer via a wireless link with the implanted device is proposed where inductive coil coupling transfers power at low frequencies while data communication is performed using extraocular and intraocular antennas at microwave frequencies. The microwave data telemetry link is characterized computationally (using Finite Difference Time Domain-FDTD) and experimentally with appropriately sized external and implanted antennas. It is observed that the head and eye tissues act as a form of dielectric lens and improve the coupling performance between the two antennas (with intraocular antenna embedded in the eye ball) as compared to coupling in free space. The data telemetry link is characterized with novel small microstrip patch and planar wire dipole as intraocular antennas. An electromagnetic and thermal analysis of the operation of such a visual prosthesis is performed. Electromagnetic power deposition in the head is evaluated in terms of Specific Absorption Rate (SAR). Temperature rise in the tissues is characterized by computationally discretizing and implementing the bio-heat equation in three dimensions in an anatomically accurate head model.
SOI for Frequency Synthesis in RF Integrated Circuits
(2003-05-01) Marks, Jeffery; Dr. Wentai Liu, Committee Chair; Dr. Brian Hughes, Committee Member; Dr. Gianluca Lazzi, Committee Member
The purpose of this research has been to explore the use of the Honeywell silicon on insulator fabrication process for use in a frequency synthesizer. The research includes the fabrication of a frequency synthesizer and ring oscillators which are used to evaluate the fabrication process. Experimental results are compared to the theoretical results, providing some insight into circuit design with the silicon on insulator process. Recommendations are presented to enhance the frequency stability of such circuits. A novel method for reducing phase noise in ring oscillators through manipulation of the floating body is also presented.
Theoretical Analysis and Design Methodologies for Low Noise Amplifiers based on Tunable Matching Networks
(2008-07-07) Yelten, Mustafa Berke; Dr. Brian Hughes, Committee Member; Dr. Wm. Rhett Davis, Committee Member; Dr. Kevin G. Gard, Committee Chair