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

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Analytical Model of Particle Motion in Optical Interference Landscapes and Laminar Flow
(2006-12-11) Conover, Brandon Lee; Dr. Orlin D. Velev, Committee Member; Dr. John Muth, Committee Member; Dr. Michael J. Escuti, Committee Chair
Optically defined one- and two-dimensional potential energy "landscapes" can create characteristic forces and torques on nano- and micro-scale spheroidal particles that may be specifically tailored to meet the manipulation and measurement needs within colloidal hydrodynamic systems. Similar to optical tweezers, optical landscapes are able to selectively sort, trap, mix, align, and order mesoscale particles, yet they hold the potential to perform these tasks on a massively parallel scope. While recent publications have provided both experimental and theoretical support of optical landscapes' capabilities, none to date have derived an order-of-magnitude approximation of the response of spheroidal particles within them. While almost all analytical models of particle motion reported so far are limited to spheres, many particles of interest are in fact shaped like disks and rods (e.g. blood cells, nanowires). This work advances toward the goal of describing complete spheroidal particle response to laminar flow and general optical landscapes of one- and two-dimensions. Here we derive the optically induced force and torque from first principles, resulting in a model capable of predicting results in agreement with previous experiments and theory. A key prediction of our model is that highly selective trapping within the landscapes can be achieved based on shape, in addition to size as described in the literature. In general, we find that as particles become more oblate or prolate, they become easier to trap as compared to spherical particles with an equivalent volume. Additionally, we find that a trapped elliptical particle will align in its lowest energy orientation as dictated by the shape of the optical landscape. Finally, we provide a brief comparison of one- and two-dimensional landscapes and their effects on spheroidal particles.
Characterization of Vertical Cavity Surface Emitting Lasers With Electrical and Optical Derivative Spectroscopy
(2003-12-11) Stanton, Brandon Matthew; Dr. Robert Kolbas, Committee Chair; Dr. John Muth, Committee Member; Dr. Salah Bedair, Committee Member
The motivation behind this work is to use derivative spectroscopy to better understand the inner workings of Vertical Cavity Surface Emitting Lasers (VCSELs) provided by Honeywell Inc. Derivative spectroscopy was used to investigate two types of Honeywell VCSELs, Oxide confined VCSELs and Proton bombarded VCSELs. To quantify the devices I-V (current-voltage) and P-I (power-current) electrical and optical measurements were used to show the devices have no major problems and that the measurements are reproducible. The I-V and P-I curves were taken to initially characterize devices. Having these curves supplies basic information such as laser threshold and data points for the slope of the operating regime. Using a voltage modulation technique derivative measurements dI/dV, d2IdV2, dL/dV were obtained and revealed subtle nonlinearities in the I-V and P-V data. Near field images of the optical output was correlated with the electrical measurements, and three mechanisms were identified that could be the cause of the derivative structure of the I-V curves.
The Development of Textile Based Acoustic Sensing Arrays for Sound Source Acquisition
(2003-07-25) Luthy, Kyle Anthony; Dr. Behnam Pourdeyhimi, Committee Member; Dr. Edward Grant, Committee Chair; Dr. John Muth, Committee Member; Dr. H Troy Nagle, Committee Member
This research project dealt primarily with the production of an electronic textiles (etextiles) demonstrator. The goal of electronic textiles is to integrate textiles technology and electronics to create large area conformal surfaces with embedded electronics. Here, the etextiles demonstrator serves as an acoustic array for sound source localization and tracking. To create portable acoustic arrays on a flexible textile substrate, an understanding of textile designs and textile processes was obtained. This research resulted in the fabrication of woven substrates with conducting lines and embedded microphone windscreens. Similarly, an understanding of the design and manufacture of flexible substrates for electronics had to be gained in order to produce miniature electronic circuits that will flex when embedded in a textile substrate. The acoustic array technology developed includes microphone arrays with their associated software for data capture and analysis, a multiplexer circuit on a flexible Kapton substrate, and a UC-Berkeley mote-based technology for use with a custom miniature microphone amplification system. Ultimately, these arrays are used to demonstrate sound localization by triangulation as well as via the spatial filtering technique of beamforming. Experiments were performed to compare different array sizes and geometries in both simulation and real world practice for a variety of target frequencies. Mote performance in the role of beamforming is compared to simulation as well as a commercially available system. Although not as ideal as in simulation, the results achieved are comparable to those of the professional system tested against.
Electronica Devices and Interface Strategies for Nanotechnology
(2007-04-12) Di Spigna, Neil Halen; Dr. Veena Misra, Committee Member; Dr. Paul Franzon, Committee Chair; Dr. John Muth, Committee Member; Dr. Gregory Parsons, Committee Member
Evaporation of ultra-thin layers of refractory metals onto glass substrates represents a relatively simple method of fabricating discontinuous metal films. The utility of these films in nanotechnology is based on the ability to control their morphology. In this thesis, control of discontinuous palladium films is demonstrated as the morphology is tailored for various applications. First, the films are successfully engineered to provide molecular scaffolding in the NanoCell. A dependency of the film morphology on the pattern density is observed which potentially could be exploited to provide wafer-scale morphology tuning with only a single evaporation. Next, electrical characterization of gold nanocrystal capacitors showed significant increases in the flat band voltage shift as the gold particle density increased. The density scaling of gold and palladium films was investigated revealing a linear dependence of gold on decreasing evaporation thickness and an exponential dependence for palladium. A palladium particle density of 1.03 x 10¹² particles cm⁻² was achieved, exceeding the theoretical target density for non-volatile memory applications. A novel technique to further increase this particle density is demonstrated. Another application for discontinuous metal films is for stochastic interface strategies. Interfacing the nanoworld with the microworld represents a critical challenge to fully integrated nanosystems. Unfortunately, not all applications can tolerate random or incomplete connectivity that can result from stochastic solutions. Therefore, a novel structure is presented that permits complete and deterministic cross-connect of orthogonal wiring arrays without the need for any critical translational alignment. Deterministically connecting 10nm wires directly to 3 µ wires would require a translational alignment to within only about 6 µ. It is shown that there is no restriction placed on the minimum nanowire pitch and that the design is independent of the technology used to fabricate the nanowires. The process is relatively simple and is presented from a fabrication perspective, critically evaluating the effect of potential processing errors on the design. A proof-of-concept structure is fabricated and analyzed, demonstrating the feasibility of this design.
The EvBot II: An Enhanced Evolutionary Robotics Platform Equipped with Integrated Sensing for Control
(2003-04-09) Mattos, Leonardo Serra; Dr. Troy Nagle, Committee Member; Dr. John Muth, Committee Member; Dr. Edward Grant, Committee Chair; Dr. Mark White, Committee Member
The research presented in this thesis describes the design and development of the EvBot II, a small, computationally powerful, and robust evolutionary robotics platform equipped with an acoustic array system. The EvBot II represents the next generation of autonomous robots for distributed robot-colony research, and its design has expanded the sensing capabilities and the overall performance of the EvBot robots by the incorporation of two microcontroller units, shaft encoders and a complete acoustic array system for tracking and navigation purposes. The design, development and test of this new robot is described in detail throughout this thesis, including the design of an USB data acquisition system capable of simultaneously sampling eight audio channels as required for the realization of the added acoustic array system. Experiments designed to evaluate the performance of this new robot and its components are also described in this thesis, as well as experimental results showing that it is a well-suited platform for the study of evolutionary robotics, distributed robot-colonies and sensors technologies.
A Linear Base Articulated Robot Arm for Surgical Endoscopy
(2006-05-18) Kracht, Aaron Arthur; Dr. John Muth, Committee Member; Dr. Ola Harrysson, Committee Member; Dr. Edward Grant, Committee Chair
This project involved developing a surgical robot assistant using an articulated robot running on a linear axis. The research concentrated on studying the localization of an endoscopic tool. The kinematics involved in this type situation requires that a constant point in space (trocar point) is maintained along a rigid tool while repositioning the manipulator. Results show that the localization algorithm and interactive interface developed is capable of using this unique robot configuration to perform the desired task. For this system, error was used as the performance metric. Positioning of the endoscopic manipulator relative to the world coordinate frame was possible to within 0.05 inch. Error in maintaining a constant point in space is evident during repositioning however this was caused by limitations in the robot arm.
Mobile Robotic Navigation and Control for Large-Scale Wireless Sensor Network Repair
(2009-08-04) Luthy, Kyle Anthony; Dr. Edward Grant, Committee Chair; Dr. John Muth, Committee Member; Dr. Thomas C. Henderson, Committee Member; Dr. H. Troy Nagle, Committee Member; Dr. Mihail Sichitiu, Committee Member
Wireless Sensor Networks (WSNs) have the potential to provide a wealth of high resolution sensory data, both temporally and spatially, over large areas and for long periods of time, but can be limited in effectiveness when a sensor node loses power or becomes damaged. The quality of the sensor network data is also reliant on the underlying network connectivity and can be degraded by imprecise deployments, and unforeseen changes in the network structure over time such as changes in weather conditions. The ability to use autonomous mobile robotic platforms to repair or replace bad sensor nodes, or to map out WSNs to identify weak nodes, has potential to enhance the performance of WSNs and improve their robustness. This dissertation investigates: 1) WSN connectivity issues over the lifetime of a network, and 2) identifying and repairing disconnects within a WSN using an autonomous robot. The effects of asymmetric links between WSN nodes and the best methods to model networks composed of asymmetric nodes were studied in depth. It was found that for networks requiring bidirectional links that the use of a disk model was optimal; however, for networks with asymmetric links, elliptical or irregular models were preferred. Thus in situations where asymmetries are permitted, more efficient network connectivity is obtained using elliptical or irregular models. Modeling, simulation, experimentation, and analysis, show that when a deployed WSN reaches a high nodal density, the network disconnects can be repaired by strategic placement of only a few nodes. The autonomous placement and repair of network disconnects was studied using the received signal strength (RSS) of messages within the WSN to navigate and control a robotic platform. This approach allows the control hardware of the mobile robot to use the same technology as that used by the WSN nodes. It is further shown by physical experiments that when the autonomous mobile robotic platform interacts directly with the RF signal transmitted from a single WSN node, that that mobile robot can carry out collision detection and obstacle avoidance tasks commonly found in mobile robotics research. Lastly, RSS has been shown to be useful for navigating around the perimeter of a deployed WSN. Using RSS for navigation and to provide a mobile node is shown to extend the range of the WSN, and to allow single-hop disconnects to be identified and repaired. Experiments were conducted both in simulation and in the physical world using a six-node WSN to prove that navigation based on RSS could repair a WSN. The speed of RSS based repair of WSNs is improved if the nodes on the perimeter of the WSN are first identified by the WSN and this information is provided to the robot. An algorithm was developed that uses local neighborhood computation, one based on the convex hull, to determine whether or not a node lies on the perimeter of the WSN. The developed algorithm performed equally as well as, or better than, the distributed and centralized detection algorithms of others, and was implemented on a twenty-five node WSN.
Optical Hardware Tradeoffs for All Optical Multicast
(2002-07-12) Chandrasekar, Karthik; Dr. Paul D. Franzon, Committee Chair; Dr. John Muth, Committee Member; Dr. Zhibo Zhang, Committee Member
All Optical WDM Networks are fast becoming the natural choice for future backbones and in order to meet the exponentially increasing traffic demands, it would be beneficial to support all optical multicast. One way to support multicast is to provide optical splitters at various switching nodes along the network. The main contribution of this thesis is in demonstrating that all optical multicast can be made practical for both 1:2 splitters and 1:N splitters through the proper incorporation of in-line EDFA's and other optical hardware components available off the shelf. Using electronics for 3-R regeneration at the intermediate nodes is costly and hence our model uses EDFA's. Most previous work in this direction has addressed multicast feasibility from an architectural standpoint while this thesis discusses issues from a physical designer's perspective. An All Optical CAD simulation tool from Virtual Photonics was used to simulate a variety of multicast networks taking into account relevant Nonlinear effects such as chromatic dispersion, four wave mixing, stimulated Raman scattering and all phenomena commonly encountered in Cascaded EDFA chains such as Accumulated Spontaneous emission noise, SNR Transients and Gain Saturation.
Polytype Stability, Microstructural Evolution, and Impurities at the Interface of Homoepitaxial 4H-SiC(1120) Thin Films Grown via Hot-Wall Chemical Vapor Deposition.
(2007-06-04) Bishop, Seann; Dr. Robert F. Davis, Committee Chair; Dr. Lew Reynolds, Committee Member; Dr. Raoul Schlesser, Committee Member; Dr. John Muth, Committee Member; Dr. Nadia El-Masry, Committee Member
The electronic properties of 4H-SiC make it a leading semiconductor material for high-power applications. Despite advances in SiC crystal growth, devices fabricated in 4H-SiC(0001) continue to be limited by defects like micropipes, dislocations and stacking faults. Investigations performed here on non-basal 4H-SiC have demonstrated micropipe-free, a-plane 4H-SiC films comparable with conventional 4H-SiC(0001). Improved device performance has been achieved for p-i-n rectifiers fabricated in a-plane 4H-SiC. Hot-wall chemical vapor deposition (CVD) is the most widely used growth process employed to meet the material demands for 4H-SiC-based high-power electronics; however, the suitability of this technique for the growth of thin films (<10 μm) is not well established. A detailed analysis of the epitaxial growth of a-plane 4H-SiC thin films by vertical, hot-wall CVD has been performed in this work. Two growth regimes were identified and termed sublimation growth and precursor growth. In the former, the SiC coating decomposes and results in the in-situ (sublimation) growth of epitaxial SiC films. It is proposed that in-situ layer aids in subsequent thin film growth from reactant gases. Transmission electron microscopy revealed areas without observable defects and an indistinguishable interface between the substrate and sublimation grown layer. Aluminum impurity concentrations to 3E18 per cc. were identified near the interface with the substrate. The influence of these impurities on the cathodoluminescence spectrum of 4H-SiC was studied. A model based on boundary layer theory was developed to explain the origin and the profile of the aluminum impurities. Secondary ion mass spectrometry revealed the SiC coating to be the major source of aluminum impurities. An argon diluent reduced the concentration of aluminum at the interface to 2E17 per cc. Films deposited via precursor growth exhibited specular surfaces. Optical and structural characterization showed the films replicate the polytype of the underlying substrate exactly. The microstructural evolution of a-plane 4H-SiC and III-nitride films was also investigated. 4H-SiC films showed evidence of step-flow growth in the sublimation-driven regime, while both step-flow and terrace nucleation and growth were observed in the precursor-driven regime. AlN initially grew via the Stranski-Krastanov mode on 4H-SiC , while the Volmer-Weber mode was observed for GaN on AlN.
Ultraviolet Detectors and Focal Plane Array Imagers Based on AlxGa1-xN P-I-N Photodiodes
(2004-03-15) Long, Joseph Preston; Dr. John Muth, Committee Member; Dr. Robert Nemanich, Committee Member; Dr. Jan Schetzina, Committee Chair
This research has been conducted in order to address the absence of effective solid-state ultraviolet (UV) detectors and imagers. Despite the wide range of advances in visible and infrared imagery, until recently there have been no semiconductor devices under development for imaging strictly in the ultraviolet region of the spectrum. Much of the difficulty in creating such devices has been due to the lack of appropriate materials; however, the development of the group III-nitrides (III-N), including materials such as GaN and AlGaN, has provided a solution to this dilemma. The AlxGa1-xN based devices synthesized during this research were grown via organo-metallic vapor phase epitaxy and processed using standard photolithography, e-beam evaporation, and reactive ion etching processes. Focal plane arrays were subsequently bump bonded to silicon read-out integrated circuits (ROICs), which were then wire bonded to 84-pin leadless chip carriers. A specialized video camera and focal plane array evaluation software were used to test the imagers. The devices exhibit very low noise and very high sensitivity to ultraviolet radiation. Excellent quality UV images have been obtained for both 128x128 and 320x256 large format hybridized focal plane arrays. These new devices may find widespread usage in a number of applications that require sensitive UV detectors and UV imagers but where the cost, size, and power requirements of a photomultiplier tube cannot be justified.