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Articles 1 - 30 of 42
Full-Text Articles in Engineering
The Effect Of Contact Length On Adhesion Between Carbon Nanotubes On Silicon Dioxide, Robert C. Davis, Kaylee Mcelroy, Aaron R. Hopkins
The Effect Of Contact Length On Adhesion Between Carbon Nanotubes On Silicon Dioxide, Robert C. Davis, Kaylee Mcelroy, Aaron R. Hopkins
Faculty Publications
The force of adhesion was measured for single walled carbon nanotubes grown over lithographically defined silicon dioxide trenches. We varied contact lengths between the nanotubes and silicon dioxide from 230 to 850 nm. Suspended nanotubes were pushed vertically into the trenches with an atomic force microscope tip, causing them to slip along the surface. Previous work done at shorter contact lengths found that tension was constant with contact length [J. D. Whittaker et al., Nano Lett. 6, 953 (2006)]. This study finds that when the nanotube contact length approaches 1 µm, the tension at which nanotubes slip begins to increase …
Optimizing Wireless Network Throughput: Methods And Applications, Pengchang Zhan
Optimizing Wireless Network Throughput: Methods And Applications, Pengchang Zhan
Theses and Dissertations
Ever since Marconi succeeded in his first demonstration on the possibility to communicate over the air overseas about a century ago, wireless communications have experienced dramatic improvements. Today's world sees the penetration of wireless communications into human life almost everywhere, from a simple remote control for TV to a cellular phone. With a better understanding of the adverse nature of the wireless propagation channels, engineers have been able to invent various clever techniques, i.e. Multiple Input Multiple Output (MIMO) technology, spread spectrum communications, Orthogonal Frequency Division Multiplexing (OFDM) to name a few, to achieve fast and reliable communications over each …
Low-Altitude Road Following, Using Strap-Down Cameras On Miniature Aerial Vehicles, Joseph M. Egbert
Low-Altitude Road Following, Using Strap-Down Cameras On Miniature Aerial Vehicles, Joseph M. Egbert
Theses and Dissertations
Miniature air vehicles (MAVs) are particularly well suited for short-distance, over-the-horizon, low-altitude surveillance and reconnaissance tasks. New camera and battery technologies have greatly increased a MAVs potential for these tasks. This thesis focuses on aerial surveillance of borders and roads, where a strap-down camera is used in-the-loop to track a border or road pathway. It is assumed that quality tracking requires that the pathway always remain in the footprint of the camera. The objective of this thesis is to explore roll-angle and altitude-above-ground-level constraints imposed on a bank-to-turn MAV due to the requirement to keep the pathway in the footprint …
Synthesis Of Optimal Arrays For Mimo And Diversity Systems, Britton T. Quist
Synthesis Of Optimal Arrays For Mimo And Diversity Systems, Britton T. Quist
Theses and Dissertations
This thesis proposes a method for determining the optimal antenna element radiation characteristics which maximize diversity gain given a specific power angular spectrum of the propagation environment. The method numerically constructs the eigenfunctions of the covariance operator for the scenario subject to constraints on the power radiated by each antenna as well as the level of supergain allowed in the solution. The optimal antenna characteristics are produced in terms of radiating current distributions along with their resulting radiation patterns. The results reveal that the optimal antennas can provide significantly more diversity gain than that provided by a simple practical design. …
Low Loss Hybrid Waveguide Electric Field Sensor Based On Optical D-Fiber, Eric K. Johnson
Low Loss Hybrid Waveguide Electric Field Sensor Based On Optical D-Fiber, Eric K. Johnson
Theses and Dissertations
This thesis presents the fabrication of a low loss hybrid waveguide electric field(E-field) sensor based on optical D-fiber. This novel E-field sensor is formed as part of a contiguous fiber resulting in a flexible and small cross-section device that can be embedded into electronic circuitry. The in-fiber nature of this sensor also eliminates the need for alignment and packaging that conventional sensors need. An optical fiber can detect electric fields when the core of the fiber is partially removed and replaced with an electro-optic polymer. This polymer causes a change in the index of refraction in the waveguide of the …
Space-Time Coding With Offset Modulations, N. Thomas Nelson
Space-Time Coding With Offset Modulations, N. Thomas Nelson
Theses and Dissertations
In this dissertation it is shown that the telemetry versions of Feher-patented QPSK (FQPSK-JR) and shaped offset QPSK (SOQPSK-TG) can be interpreted as both cross-correlated, trellis-coded quadrature modulation (XTCQM) and continuous phase modulation (CPM). Based on these representations, both modulations can be detected with near optimal bit error rate performance using a common detector that is formulated as either an XTCQM detector, a traditional CPM detector, or a pulse amplitude modulation (PAM) detector (due to the PAM decomposition of the CPM representations of these modulations). In addition it is shown that the complexity of the XTCQM detector for SOQPSK-TG can …
Low-Voltage Analog Cmos Architectures And Design Methods, Kent Downing Layton
Low-Voltage Analog Cmos Architectures And Design Methods, Kent Downing Layton
Theses and Dissertations
This dissertation develops design methods and architectures which allow analog circuits to operate at VT + 2Vds,sat, the minimum supply for CMOS circuits with all transistors in the active region where Vds,sat is the drain to source saturation voltage of a MOS transistor. Techniques which meet this criteria for rail-to-rail input stages, gain enhancement stages, and output stages are discussed and developed. These techniques are used to design four fully-differential rail-to-rail amplifiers. The highest gain is shown to be attained using a drain voltage equalization (DVE) or active-bootstrapping technique which produces more than 100dB of gain in a two stage …
Polarization Rotation Correction In Radiometry: An Error Analysis, David G. Long, Derek Hudson, Jeffrey R. Piepmeier
Polarization Rotation Correction In Radiometry: An Error Analysis, David G. Long, Derek Hudson, Jeffrey R. Piepmeier
Faculty Publications
Yueh proposed a method of using the third Stokes parameter TU to correct brightness temperatures such as Tv and Th for polarization rotation. This paper presents an extended error analysis of the estimation of Tv , Th, and TQ equiv Tv - Th by Yueh's method. In order to carry out the analysis, we first develop a forward model of polarization rotation that accounts for the random nature of thermal radiation, receiver noise, and (to first order) calibration. Analytic formulas are then derived for the bias, standard deviation (STD), and root-mean-square error (RMSE) of estimated TQ, Tv , and Th, …
Byu Wideband Mimo Channel Sounder Technical Reference Manual, Jon W. Wallace
Byu Wideband Mimo Channel Sounder Technical Reference Manual, Jon W. Wallace
Faculty Publications
This document serves as a technical reference manual for the wideband multiple-input multipleoutput (MIMO) wireless channel sounder developed at the Wireless Research Laboratory at Brigham Young University. The development of this system is considered an "open hardware project," which means that the details of the system may be freely used by others interested in designing and building similar systems. Also, it is hoped that the open hardware methodology will lead to fruitful cooperation in improving the system and sharing ideas.
High-Speed Data Acquisition And Fpga Detected Pulse Blanking System For Interference Mitigation In Radio Astronomy, Micah Alexander Lillrose
High-Speed Data Acquisition And Fpga Detected Pulse Blanking System For Interference Mitigation In Radio Astronomy, Micah Alexander Lillrose
Theses and Dissertations
Radio astronomy is the discipline dedicated to the study of celestial emissions in the radio band from a few MHz to 300 GHz. In recent years, spurious emissions from man-made devices that operate at these frequencies have made detection of astronomical signals difficult. These harmful RF transmissions are called radio frequency interference (RFI). One strategy to remove RFI is to apply spatial filtering using an array antenna. This thesis documents the development of a high-speed data acquisition system used to record data from 7- and 19-element phased array feeds. The system supports synchronous sampling over all channels and streams data …
Experiments In Cooperative Timing For Miniature Air Vehicles, Derek R. Nelson, Timothy W. Mclain, Randal W. Beard
Experiments In Cooperative Timing For Miniature Air Vehicles, Derek R. Nelson, Timothy W. Mclain, Randal W. Beard
Faculty Publications
This paper presents experimental results for two cooperative timing missions carried out using a team of three miniature air vehicles (MAVs). Using a cooperative timing algorithm based on coordination functions and coordination variables, the MAV team executed a series of simultaneous arrival and cooperative fly-by missions. In the presence of significant wind disturbances, the average time difference between the first and last vehicle in the simultaneous arrival experiments was 1.6 s. For the cooperative fly-by experiments, the average timing error between vehicle arrivals was 0.6 s. These results demonstrate the practical feasibility of the cooperative timing approach.
Decentralized Control Of Multiple Uavs For Perimeter And Target Surveillance, Derek B. Kingston
Decentralized Control Of Multiple Uavs For Perimeter And Target Surveillance, Derek B. Kingston
Theses and Dissertations
With the recent development of reliable autonomous technologies for small unmanned air vehicles (UAVs), the algorithms utilizing teams of these vehicles are becoming an increasingly important research area. Unfortunately, there is no unified framework into which all (or even most) cooperative control problems fall. Five factors that affect the development of cooperative control algorithms are objective coupling, communication, completeness, robustness, and efficiency. We classify cooperative control algorithms by these factors and then present three algorithms with application to target and perimeter surveillance and a method for decentralized algorithm design. The primary contributions of this research are the development and analysis …
Transitions Between Hover And Level Flight For A Tailsitter Uav, Stephen R. Osborne
Transitions Between Hover And Level Flight For A Tailsitter Uav, Stephen R. Osborne
Theses and Dissertations
Vertical Take-Off and Land (VTOL) Unmanned Air Vehicles (UAVs) possess several desirable characteristics, such as being able to hover and take-off or land in confined areas. One type of VTOL airframe, the tailsitter, has all of these advantages, as well as being able to fly in the more energy-efficient level flight mode. The tailsitter can track trajectories that successfully transition between hover and level flight modes. Three methods for performing transitions are described: a simple controller, a feedback linearization controller, and an adaptive controller. An autopilot navigational state machine with appropriate transitioning between level and hover waypoints is also presented. …
Particle Filter Based Mosaicking For Forest Fire Tracking, Justin Mathew Bradley
Particle Filter Based Mosaicking For Forest Fire Tracking, Justin Mathew Bradley
Theses and Dissertations
Using autonomous miniature air vehicles (MAVs) is a cost-effective, simple method for collecting data about the size, shape, and location characteristics of a forest fire. However, noise in measurements used to compute pose (location and attitude) of the on-board camera leads to significant errors in the processing of collected video data. Typical methods using MAVs to track fires attempt to find single geolocation estimates and filter that estimate with subsequent observations. While this is an effective method of resolving the noise to achieve a better geolocation estimate, it reduces a fire to a single point or small set of points. …
A Wind And Rain Backscatter Model Derived From Amsr And Seawinds Data, Seth Niels Nielsen
A Wind And Rain Backscatter Model Derived From Amsr And Seawinds Data, Seth Niels Nielsen
Theses and Dissertations
The SeaWinds scatterometers aboard the QuikSCAT and ADEOS II satellites were originally designed to measure wind vectors over the ocean by exploiting the relationship between wind-induced surface roughening and the normalized radar backscatter cross-section. Recently, an algorithm for simultaneously retrieving wind and rain (SWR) from scatterometer measurements was developed that enables SeaWinds to correct rain-corrupted wind measurements and retrieve rain rate data. This algorithm is based on co-locating Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR) and SeaWinds on QuikSCAT data. In this thesis, a new wind and rain radar backscatter model is developed for the SWR algorithm using a …
Hardware Support For A Configurable Architecture For Real-Time Embedded Systems On A Programmable Chip, Spencer W. Isaacson
Hardware Support For A Configurable Architecture For Real-Time Embedded Systems On A Programmable Chip, Spencer W. Isaacson
Theses and Dissertations
Current FPGA technology has advanced to the point that useful embedded SoPCs can now be designed. The Real Time Processor (RTP) project at Brigham Young University leverages the advances in FPGA technology with a system architecture that is customizable to specific applications. A simple real-time processor has been designed to provide support for a hardware-assisted real-time operating system providing fast context switches. As part of the hardware RTOS, the following have been implemented in hardware: scheduler, register banks, mutex, semaphore, queue, interrupts, event, and others. A novel circuit called the Task-Resource Matrix has been created to allow fast inter/intra processor …
Compilation And Generation Of Multi-Processor On A Chip Real-Time Embedded Systems, Randall S. Klingler
Compilation And Generation Of Multi-Processor On A Chip Real-Time Embedded Systems, Randall S. Klingler
Theses and Dissertations
Current FPGA technology has advanced to the point that useful embedded System-on-Programmable-Chips (SoPC)s can now be designed. The Real Time Processor (RTP) project leverages the advances in FPGA technology with a system architecture that is customizable to specific real-time applications. The design and implementation of the framework for architecting such a system from ANSI-C code is presented. The Small Device C Compiler (SDCC) was retargeted to the RTP architecture and extended to produce a generator directive file. The RTPGen hardware generator was created to consume the directive file and produce a highly customized top-level structural VHDL file that can be …
Time-Varying Mimo Channels: Parametric Statistical Modeling And Experimental Results, Michael A. Jensen, Shuangquan Wang, Ali Abdi, Jari Salo, Hassan M. El-Sallabi, Jon W. Wallace, Pertti Vainikainen
Time-Varying Mimo Channels: Parametric Statistical Modeling And Experimental Results, Michael A. Jensen, Shuangquan Wang, Ali Abdi, Jari Salo, Hassan M. El-Sallabi, Jon W. Wallace, Pertti Vainikainen
Faculty Publications
Accurate characterization of multiple-input multiple-output (MIMO) fading channels is an important prerequisite for the design of multiantenna wireless-communication systems. In this paper, a single-bounce two-ring statistical model for the time-varying MIMO flat fading channels is proposed. In the model, both the base and mobile stations are surrounded by their own ring of scatterers. For the proposed model, a closed-form expression for the spatio-temporal cross-correlational function between any two subchannels is derived, assuming single-bounce scattering. The new analytical expression includes several key physical parameters of interest such as the mean angle-of-departure, the mean angle-of-arrival, the associated angle spreads, and the Doppler …
Information Consensus And Its Application In Multi-Vehicle Cooperative Control, Ella Atkins, Randal Beard, Wei Ren
Information Consensus And Its Application In Multi-Vehicle Cooperative Control, Ella Atkins, Randal Beard, Wei Ren
Faculty Publications
In the last two decades, advances in networking and distributed computing have facilitated a paradigm shift from large, monolithic mainframe computers to networks of less expensive, less powerful workstations. One motivation for multi-vehicle systems is to achieve the same gains for mechanically controlled systems as has been gained in distributed computation. Rather than having a single monolithic (and therefore expensive and complicated) machine do everything, the hope is that many inexpensive, simple machines, can achieve the same, or enhanced functionality, through coordination. In essence, the objective is to replace expensive complicated hardware with software and multiple copies of simple hardware. …
Three Enabling Technologies For Vision-Based, Forest-Fire Perimeter Surveillance Using Multiple Unmanned Aerial Systems, Ryan S. Holt
Three Enabling Technologies For Vision-Based, Forest-Fire Perimeter Surveillance Using Multiple Unmanned Aerial Systems, Ryan S. Holt
Theses and Dissertations
The ability to gather and process information regarding the condition of forest fires is essential to cost-effective, safe, and efficient fire fighting. Advances in sensory and autopilot technology have made miniature unmanned aerial systems (UASs) an important tool in the acquisition of information. This thesis addresses some of the challenges faced when employing UASs for forest-fire perimeter surveillance; namely, perimeter tracking, cooperative perimeter surveillance, and path planning. Solutions to the first two issues are presented and a method for understanding path planning within the context of a forest-fire environment is demonstrated. Both simulation and hardware results are provided for each …
Optimization Of Nano-Magneto-Optic Sensitivity Using Dual Dielectric Layer Enhancement, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, S. Kwon, B. Harteneck, S. Cabrini, J. Bokor
Optimization Of Nano-Magneto-Optic Sensitivity Using Dual Dielectric Layer Enhancement, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, S. Kwon, B. Harteneck, S. Cabrini, J. Bokor
Faculty Publications
We discuss maximization of the sensitivity of magneto-optical detection of single nanomagnets. We show that a combination of optimized dielectric coating on the magnets with an antireflection coated substrate can increase the areal magneto-optic sensitivity by about three orders of magnitude in the deep nanometer range. A dual layer nanofabrication process is developed to implement this approach, and magnetization switching of single nickel nanomagnets with 50 nm diameter is demonstrated.
Performance Of Mimo Space-Time Coding Algorithms On A Parallel Dsp Test Platform, Beau C. Neal
Performance Of Mimo Space-Time Coding Algorithms On A Parallel Dsp Test Platform, Beau C. Neal
Theses and Dissertations
Commercial Off The Shelf (COTS) hardware has the advantages of low cost, modularity, and is easily upgraded. For Multiple-Input Multiple-Output (MIMO) space-time algorithms to be practical they must have the processing capability to execute in real-time. This makes COTS ideal for real-time MIMO research where the processing power increases exponentially with a linear increase in antennas. The BYU Electrical Engineering wireless lab has designed and built an eight processor transmitter and a twenty processor receiver to research and develop MIMO wireless communication. The Alamouti, 2 x 2 and 4 x 4 differential space-time MIMO algorithms have been partially implemented on …
Optimal Noise Matching For Mutually-Coupled Arrays, Michael A. Jensen, Karl F. Warnick
Optimal Noise Matching For Mutually-Coupled Arrays, Michael A. Jensen, Karl F. Warnick
Faculty Publications
From classical two-port noise theory, the noise figure of an amplifier is minimized when a source is matched to a particular optimal reflection coefficient at the amplifier input. In this paper, we show that this result extends in a natural way to the multiport case, with a coupled N-port source network such as an array antenna connected by a multiport matching network to the inputs of N low-noise amplifiers. For optimal noise performance, the matching network must decouple the array and present isolated, individually noise-matched ports to the amplifier inputs.
Band Discontinuity Measurements Of The Wafer Bonded Ingaas/Si Heterojunction, Aaron R. Hawkins, Kyle S. Mckay, Felix P. Lu, Jungsang Kim, Changhyun Yi, April S. Brown
Band Discontinuity Measurements Of The Wafer Bonded Ingaas/Si Heterojunction, Aaron R. Hawkins, Kyle S. Mckay, Felix P. Lu, Jungsang Kim, Changhyun Yi, April S. Brown
Faculty Publications
p-type InGaAs/Si heterojunctions were fabricated through a wafer fusion bonding process. The relative band alignment between the two materials at the heterointerface was determined using current-voltage (I-V) measurements and applying thermionic emission-diffusion theory. The valence and conduction band discontinuities for the InGaAs/Si interface were determined to be 0.48 and 0.1 eV, respectively, indicating a type-II band alignment.
On-Chip Surface-Enhanced Raman Scattering Detection Using Integrated Liquid-Core Waveguides, Aaron R. Hawkins, Evan J. Lunt, Phillip Measor, Leo Seballos, Dongliang Yin, Jin Z. Zhang, Holger Schmidt
On-Chip Surface-Enhanced Raman Scattering Detection Using Integrated Liquid-Core Waveguides, Aaron R. Hawkins, Evan J. Lunt, Phillip Measor, Leo Seballos, Dongliang Yin, Jin Z. Zhang, Holger Schmidt
Faculty Publications
The authors demonstrate surface-enhanced Raman scattering (SERS) detection on an optofluidic chip. Interconnected solid- and liquid-core antiresonant reflecting optical waveguides (ARROWs) form a planar beam geometry that allows for high mode intensities along microfluidic channels containing molecules optimized for SERS. The excitation power and concentration dependence of SERS from rhodamine 6G (R6G) molecules adsorbed to silver nanoparticles were systematically studied. The data can be described by a model that takes into account the microphotonic structure. Detection sensitivity to a minimum concentration of 30 nM is found, demonstrating the suitability of ARROW-based optofluidic chips for high sensitivity detection with molecular specificity
Size Dependent Damping In Picosecond Dynamics Of Single Nanomagnets, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, Liddle A. Kwon, J. Bokor
Size Dependent Damping In Picosecond Dynamics Of Single Nanomagnets, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, Liddle A. Kwon, J. Bokor
Faculty Publications
The authors use time-resolved cavity-enhanced magneto-optical Kerr spectroscopy to study the damping of magnetization precession in individual cylindrical nickel nanomagnets. A wide range of shapes (diameters of 5 µm–125 nm and aspect ratio: 0.03–1.2) is investigated. They observe a pronounced difference in damping between the micro- and nanomagnets. Microscale magnets show large damping at low bias fields, whereas nanomagnets exhibit bias field-independent damping. This behavior is explained by the interaction of in-plane and out-of-plane precession modes in microscale magnets that results in additional dissipative channels. The small and robust damping values on the nanoscale are promising for implementation of controlled …
An Overview Of Mav Research At Brigham Young University, Timothy W. Mclain, Randal W. Beard, D. Blake Barber, Nathan B. Knoebel
An Overview Of Mav Research At Brigham Young University, Timothy W. Mclain, Randal W. Beard, D. Blake Barber, Nathan B. Knoebel
Faculty Publications
This paper summarizes research efforts at Brigham Young University related to the control of miniature aerial vehicles (MAVs). Recent results in the areas of vector field path following, precision landing and target prosecution, target localization, obstacle detection and avoidance, tailsitter aircraft control, and cooperative control are presented.
Spatial And Temporal Behavior Of Microwave Backscatter Directional Modulation Over The Saharan Ergs, David G. Long, Haroon Stephen
Spatial And Temporal Behavior Of Microwave Backscatter Directional Modulation Over The Saharan Ergs, David G. Long, Haroon Stephen
Faculty Publications
Radar backscatter (σ˚) from ergs is modulated with view direction [incidence (θ) and azimuth (φ) angles], where the modulation characteristics reflect the surface geometry. σ˚ also varies spatially and reflects the spatial inhomogeneity of the sand surface. We use σ˚ measurements at different θ and φ angles from the NASA, European Remote Sensing satellite, and SeaWinds scatterometers to understand the relationship between wind and erg bedforms. A model incorporating the σ˚ φ-modulation and spatial inhomogeneity is proposed. Surface slope variations are related to the σ˚ spatial inhomogeneity. We compare the backscatter model results with numerically predicted wind direction data provided …
The Relationship Between Antenna Loss And Superdirectivity In Mimo Systems, Michael A. Jensen, Nicolas W. Bikhazi
The Relationship Between Antenna Loss And Superdirectivity In Mimo Systems, Michael A. Jensen, Nicolas W. Bikhazi
Faculty Publications
Multiple-input multiple-output (MIMO) communication systems can theoretically use array superdirectivity to optimally exploit the propagation channel. This superdirectivity leads to very large capacity bounds, particularly when the antennas are closely spaced. However, because superdirective behavior is difficult to achieve in practice, new capacity bounds have been formulated for the case where the level of array superdirectivity is constrained. Existing capacity analyses limit the superdirectivity in a suboptimal way. In this paper, the impact of superdirectivity in the capacity solution is limited by introducing finite ohmic loss in the transmit and receive antenna elements. Computational results reveal that even a small …
Experimental Characterization Of The Outdoor Mimo Wireless Channel Temporal Variation, Michael A. Jensen, Karl F. Warnick, Jon W. Wallace, Ajay Gummalla, Harry B. Lee
Experimental Characterization Of The Outdoor Mimo Wireless Channel Temporal Variation, Michael A. Jensen, Karl F. Warnick, Jon W. Wallace, Ajay Gummalla, Harry B. Lee
Faculty Publications
Time-variant multiple-input multiple-output (MIMO) channels are measured in an outdoor campus environment at 2.45 GHz with directional patch arrays and omnidirectional monopole arrays. A number of useful metrics are proposed for quantifying time variation in MIMO channels: eigenvalue level crossing rate, eigenvector angular deviation, and capacity loss for delayed transmit and receive channel state information (CSI). Measurements in four different environments confirm the strong correlation between angular spread of multipath and MIMO channel time variability. The rate of time variation is also strongly influenced by the type of array, indicating that directional elements may be advantageous for highly mobile environments. …