Department of Electrical and Computer Engineering

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https://hdl.handle.net/10217/100411

These digital collections include faculty/student publications, theses, dissertations, and datasets from the Department of Electrical and Computer Engineering. Due to departmental name changes, materials from the following historical department are also included here: Electrical Engineering.

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Now showing 1 - 20 of 890

Open Access
0.85 PW laser operation at 3.3 Hz and high-contrast ultrahigh-intensity λ = 400 nm second-harmonic beamline
(Colorado State University. Libraries, 2017-09-22) Wang, Yong, author; Wang, Shoujun, author; Rockwood, Alex, author; Luther, Bradley M., author; Hollinger, Reed, author; Curtis, Alden, author; Calvi, Chase, author; Menoni, Carmen S., author; Rocca, Jorge J., author; Optical Society of America, publisher
We demonstrate the generation of 0.85 PW, 30 fs laser pulses at a repetition rate of 3.3 Hz with a record average power of 85 W from a Ti:sapphire laser. The system is pumped by high-energy Nd:glass slab amplifiers frequency doubled in LiB3O5 (LBO). Ultrahigh-contrast λ = 400 nm femtosecond pulses were generated in KH2PO4 (KDP) with>40% efficiency. An intensity of 6.5 × 1021 W∕cm2 was obtained by frequency doubling 80% of the available Ti:sapphire energy and focusing the doubled light with an f∕2 parabola. This laser will enable highly relativistic plasma experiments to be conducted at high repetition rate.
Open Access
1-W cw Zn ion laser
(Colorado State University. Libraries, 1983) Meyer, J. D., author; Rocca, Jorge J., author; Collins, G. J., author; American Institute of Physics, publisher
We have obtained 1.2W of cw laser power on the 4911.6- and 4924.0-Å transitions of Zn II by exciting a He-Zn gas mixture with a dc glow discharge electron beam. In addition, 0.25-W output power has been obtained on the 6149.9-Å line of Hg+ using the same excitation scheme. The combination of electron beam ionization of rare gas atoms and subsequent charge transfer excitation to metal ion levels is shown to have the potential of significantly increasing the efficiency of ion lasers. cw multiwatt visible and ultraviolet ion lasers operating at efficiencies > 10-3 appear feasible using this excitation scheme.
Open Access
1/ƒ noise for intermittent quantum dots exhibits nonstationarity and critical exponents
(Colorado State University. Libraries, 2014-11) Sadegh, Sanaz, author; Barkai, Eli, author; Krapf, Diego, author; IOP Publishing Ltd., publisher
The power spectrum of quantum dot (QD) fluorescence exhibits 1/ƒ β noise, related to the intermittency of these nanosystems. As in other systems exhibiting 1/ƒ noise, this power spectrum is not integrable at low frequencies, which appears to imply infinite total power. We report measurements of individual QDs that address this long-standing paradox. We find that the level of 1/ƒ β noise decays with the observation time. The change of the spectrum with time places a bound on the total power. These observations are in stark contrast with most measurements of noise in macroscopic systems which do not exhibit any evidence for non-stationarity. We show that the traditional description of the power spectrum with a single exponent β is incomplete and three additional critical exponents characterize the dependence on experimental time.
Embargo
3D localization of cytoskeleton in mouse spermatids using stochastic optical reconstruction microscopy
(Colorado State University. Libraries, 2022) Sunny, Reshma, author; Krapf, Diego, advisor; Nikdast, Mahdi, committee member; Prasad, Ashok, committee member
It is estimated by the World Health Organization that globally 186 million individuals live with infertility. Studies have shown that cause of male infertility is unknown in 30 to 50% of the cases. Over the last several years teratozoospermias have been investigated and have been backtracked to events in spermatogenesis. The development of the acrosome and the manchette, protein and vesicle transport in spermatids, and sperm head shaping are crucial steps in the formation of healthy sperms. The cytoskeleton in spermatids plays a crucial role in shaping the sperm head. The acroplaxome exerts forces on the nucleus and gives the mammalian sperm head its species-specific shape, and also facilitates the proper attachment of the nuclear cap called the acrosome, containing the enzymes required for sperm penetration of the oocyte. The manchette should be intact and formed properly to have shortened diameter as spermatids differentiate so that it can constrict the base of the nucleus to shape the head, and also facilitate the transport of cargo to the base of the cell. Thus as studies have confirmed, the disruption in the organization of the cytoskeleton is a concern for infertility. Hence it is crucial to learn more about the cytoskeletal structures in spermatids. The goal of this thesis is to 3D localize these structures. The major structures we are interested in are the acroplaxome and the manchette. For this, we use a super-resolution microscopy method called Stochastic Optical Reconstruction Microscopy to image spermatid cytoskeleton. Our experiments confirmed the presence of α-tubulin in the manchette and that of F-actin in the manchette and the acroplaxome, as previously observed by researchers with 2D confocal images. We observed that the manchette reduces in diameter and progresses to the caudal portion of the cell at the later steps of differentiation and that the structure forms completely at step 10 and disassembles after step 14.
Open Access
A 2-D filtering scheme for stereo image compression using sequential orthogonal subspace updating
(Colorado State University. Libraries, 2001) Seo, Sang-Hoon, author; Azimi-Sadjadi, Mahmood R., author; IEEE, publisher
Stereo image compression involves estimating the disparity vectors that represent the amount of binocular parallax. The mismatching problems between the left and right images greatly impact the accuracy of the reconstructed image, and hence the visual effects of the reproduced 3-D image. This paper presents a new method for compensating the mismatching effects in stereo image pairs. This 2-D filtering-based scheme uses a sequential orthogonal subspace updating (SOSU) process to project an image block onto a subset of best-basis vectors. The basis vectors are selected one by one from the neighboring blocks, as well as some typical edge blocks, forming an image-dependent set of basis vectors. This leads to the optimal representation of an image block with fewer coefficients. Simulation results on two different image pairs demonstrate the effectiveness of the SOSU scheme when compared to those of the standard least squares 2-D filtering and the hybrid disparity-compensated discrete cosine transform residual encoding schemes.
Open Access
A Bayesian correction approach for improving dual-frequency precipitation radar rainfall rate estimates
(Colorado State University. Libraries, 2020-01-27) Ma, Yingzhao, author; Chandrasekar, V., author; Biswas, Sounak K., author; Journal of Meteorological Society of Japan, publisher
The accurate estimation of precipitation is an important objective for the Dual-frequency Precipitation Radar (DPR), which is located on board the Global Precipitation Measurement (GPM) satellite core observatory. In this study, a Bayesian correction (BC) approach is proposed to improve the DPR’s instantaneous rainfall rate product. Ground dual-polarization radar (GR) observations are used as references, and a log-transformed Gaussian distribution is assumed as the instantaneous rainfall process. Additionally, a generalized regression model is adopted in the BC algorithm. Rainfall intensities such as light, moderate, and heavy rain and their variable influences on the model’s performance are considered. The BC approach quantifies the predictive uncertainties associated with the Bayesiancorrected DPR (DPR_BC) rainfall rate estimates. To demonstrate the concepts developed in this study, data from the GPM overpasses of the Weather Service Surveillance Radar (WSR-88D), KHGX, in Houston, Texas, between April 2014 and June 2018 are used. Observation errors in the DPR instantaneous rainfall rate estimates are analyzed as a function of rainfall intensity. Moreover, the best-performing BC model is implemented in three GPM-overpass cases with heavy rainfall records across the southeastern United States. The results show that the DPR_BC rainfall rate estimates have superior skill scores and are in better agreement with the GR references than with the DPR estimates. This study demonstrates the potential of the proposed BC algorithm for enhancing the instantaneous rainfall rate product from spaceborne radar equipment.
Open Access
A biosensor system with an integrated CMOS microelectrode array for high spatio-temporal electrochemical imaging
(Colorado State University. Libraries, 2019) Tedjo, William, author; Chen, Thomas, advisor; Tobet, Stuart, committee member; Collins, George, committee member; Wilson, Jesse, committee member
The ability to view biological events in real time has contributed significantly to research in life sciences. While optical microscopy is important to observe anatomical and morphological changes, it is equally important to capture real-time two-dimensional (2D) chemical activities that drive the bio-sample behaviors. The existing chemical sensing methods (i.e. optical photoluminescence, magnetic resonance, and scanning electrochemical), are well-established and optimized for existing ex vivo or in vitro analyses. However, such methods also present various limitations in resolution, real-time performance, and costs. Electrochemical method has been advantageous to life sciences by supporting studies and discoveries in neurotransmitter signaling and metabolic activities in biological samples. In the meantime, the integration of Microelectrode Array (MEA) and Complementary-Metal-Oxide-Semiconductor (CMOS) technology to the electrochemical method provides biosensing capabilities with high spatial and temporal resolutions. This work discusses three related subtopics in this specific order: improvements to an electrochemical imaging system with 8,192 sensing points for neurotransmitter sensing; comprehensive design processes of an electrochemical imaging system with 16,064 sensing points based on the previous system; and the application of the system for imaging oxygen concentration gradients in metabolizing bovine oocytes. The first attempt of high spatial electrochemical imaging was based on an integrated CMOS microchip with 8,192 configurable Pt surface electrodes, on-chip potentiostat, on-chip control logic, and a microfluidic device designed to support ex vivo tissue experimentation. Using norepinephrine as a target analyte for proof of concept, the system is capable of differentiating concentrations of norepinephrine as low as 8µM and up to 1,024 µM with a linear response and a spatial resolution of 25.5×30.4μm. Electrochemical imaging was performed using murine adrenal tissue as a biological model and successfully showed caffeine-stimulated release of catecholamines from live slices of adrenal tissue with desired spatial and temporal resolutions. This system demonstrates the capability of an electrochemical imaging system capable of capturing changes in chemical gradients in live tissue slices. An enhanced system was designed and implemented in a CMOS microchip based on the previous generation. The enhanced CMOS microchip has an expanded sensing area of 3.6×3.6mm containing 16,064 Pt electrodes and the associated 16,064 integrated read channels. The novel three-electrode electrochemical sensor system designed at 27.5×27.5µm pitch enables spatially dense cellular level chemical gradient imaging. The noise level of the on-chip read channels allow amperometric linear detection of neurotransmitter (norepinephrine) concentrations from 4µM to 512µM with 4.7pA/µM sensitivity (R=0.98). Electrochemical response to dissolved oxygen concentration or oxygen partial pressure (pO2) was also characterized with deoxygenated deionized water containing 10µM to 165 µM pO2 with 8.21pA/µM sensitivity (R=0.89). The enhanced biosensor system also demonstrates selectivity to different target analytes using cyclic voltammetry to simultaneously detect NE and uric acid. In addition, a custom-designed indium tin oxide and Au glass electrode is integrated into the microfluidic support system to enable pH measurement, ensuring viability of bio-samples in ex vivo experiments. Electrochemical images confirm the spatiotemporal performance at four frames per second while maintaining the sensitivity to target analytes. The overall system is controlled and continuously monitored by a custom-designed user interface, which is optimized for real-time high spatiotemporal resolution chemical bioimaging. It is well known that physiological events related to oxygen concentration gradients provide valuable information to determine the state of metabolizing biological cells. Utilizing the CMOS microchip with 16,064 Pt MEA and an improved three-electrode system configuration, the system is capable of imaging low oxygen concentration with limit of detection of 18.3µM, 0.58mg/L, or 13.8mmHg. A modified microfluidic support system allows convenient bio-sample handling and delivery to the MEA surface for sensing. In vitro oxygen imaging experiments were performed using bovine cumulus-oocytes-complexes cells with custom software algorithms to analyze its flux density and oxygen consumption rate. The imaging results are processed and presented as 2D heatmaps, representing the dissolved oxygen concentration in the immediate proximity of the cell. The 2D images and analysis of oxygen consumption provide a unique insight into the spatial and temporal dynamics of cell metabolism.
Open Access
A CAD driven multiscale approach to automated inspection
(Colorado State University. Libraries, 1994) Maciejewski, Anthony A., author; Khawaja, Khalid W., author; Bouman, Charles Addison, author; Tretter, Daniel, author; IEEE, publisher
In this paper we develop a general multiscale stochastic object detection algorithm for use in an automated inspection application. Information from a CAD model is used to initialize the object model and guide the training phase of the algorithm. An object is represented as a stochastic tree, where each node of the tree is associated with one of the various object components used to locate and identify the part. During the training phase a number of model parameters are estimated from a set of training images, some of which are generated from the CAD model. The algorithm then uses a fast multiscale search strategy to locate and identify the subassemblies making up the object tree. We demonstrate the performance of the algorithm on a typical mechanical assembly.
Open Access
A clarification of the index of refraction of beta-iron disilicide
(Colorado State University. Libraries, 1988) Bost, M. C., author; Mahan, John E., author; American Institute of Physics, publisher
Previously published values of the index of refraction of beta-iron disilicide are corrected. Based on improved measurements and analysis, the undispersed value of the refractive index is 5.6. The previously published analysis of the absorption coefficient showed that the material possesses a direct forbidden energy gap of approximately 0.87 eV. The type of the transition is unchanged, but the band-gap value is slightly shifted to 0.89 eV.
Open Access
A clustered yield model for SMT boards and MCM's
(Colorado State University. Libraries, 1995) Chen, Tom W., author; Tegethoff, Mick M. V., author; IEEE, publisher
This paper describes a clustered yield model for complex surface mount technology (SMT) assemblies and multichip modules (MCM's). Based on yield modeling techniques that have been proven in the manufacturing of integrated circuits (IC's), this model uses the negative binomial distribution of defects to calculate board yield after test. Manufacturing data validates that this model accurately predicts the clustering of defects and the yield predictions are significantly better than traditional binomial models.
Open Access
A CMOS compatible optical biosensing system based on local evanescent field shift mechanism
(Colorado State University. Libraries, 2011) Yan, Rongjin, author; Lear, Kevin L., advisor; Dandy, David S., committee member; Chandrasekar, V., committee member; Notaros, Branislav, committee member
The need for label-free integrated optical biosensors has dramatically increased in recent years. Integrated optical biosensors have many advantages, including low-cost, and portability. They can be applied to many fields, including clinical diagnostics, food safety, environmental monitoring, and biosecurity applications. One of the most important applications is point-of-care diagnosis, which means the disease could be tested at or near the site of patient care rather than in a laboratory. We are exploring the issues of design, modeling and measurement of a novel chip-scale local evanescent array coupled (LEAC) biosensor, which is an ideal platform for point-of-care diagnosis. Until now, three generations of LEAC samples have been designed, fabricated and tested. The 1st generation of LEAC sensor without a buried detector array was characterized using a commercial near field scanning optical microscope (NSOM). The sample was polished and was end-fire light coupled using single mode fiber. The field shift mechanism in this proof-to-concept configuration without buried detector arrays has been validated with inorganic adlayers [1], photoresist [2] and different concentrations of CRP proteins [3]. Mode beating phenomena was predicted by the beam propagation method (BPM) and was observed in the NSOM measurement. A 2nd generation LEAC sensor with a buried detector array was fabricated using 0.35μm CMOS process at the Avogo Technologies Inc., Fort Collins, Colorado. Characterizations with both single layer patternings, including photoresist as well as BSA [4] and immunoassay complexes [5] were done with cooperative efforts from various research groups. The BPM method was used to study the LEAC sensor, and the simulation results demonstrated the sensitivity of the LEAC sensor is 16%/nm, which was proved to match well with the experimental data [6]. Different antigen/antibodies, including mouse IgG and Hspx (a tuberculosis reactive antigen), have been used to test the immunoassay ability of LEAC sensor [7]. Many useful data have been collected by using the 2nd generation LEAC chip. However, during the characterization of the Avago chips, some design problems were revealed, including incompatibility with microfluidic integration, restricted detection region, strong sidewall scattering and uncoupled light interference from the single mode fiber. To address these problems, the 3rd generation LEAC sensor chip with buried detector arrays was designed to allow real-time monitoring and compatibility with microfluidic channel integration. 3rd generation samples have been fabricated in the CSU cleanroom and the mesa detector structure has been replaced with the thin insulator detector structure to solve the problems encountered during the characterizations. PDMS microfluidic channels and a multichannel measurement system consisting of a probe card, a multiplexing/amplification circuit and a LabVIEW program have been implemented into the LEAC system. In recent years, outbreaks of fast spreading viral diseases, such as bird flu and H1N1, have drawn a lot of concern of the point-of-care virus detection techniques. To test the virus detection ability of LEAC sensor, 40nm and 200nm polystyrene nanoparticles were immobilized onto the waveguide, and the increased scattered light was collected. Sensitivities of 1%/particle and 0.04%/particle were observed for 200nm and 40nm particles respectively.
Open Access
A comparative study of five parallel genetic algorithms using the traveling salesman problem
(Colorado State University. Libraries, 1998) Roychowdhury, Vwani P., author; Siegel, Howard Jay, author; Maciejewski, Anthony A., author; Wang, Lee, author; IEEE, publisher
Parallel genetic algorithms (PGAs) have been developed to reduce the large execution times that are associated with serial genetic algorithms (SGAs). They have also been used to solve larger problems and to find better solutions. In this paper, a comparative analysis of five different coarse-grained PGAs is conducted using the traveling salesman problem as the basis of this case study. To make fair comparisons, all of these PGAs are based on the same baseline SGA, implemented on the same parallel machine (IBM SP2), tested on the same set of traveling salesman problem instances, and started from the same set of initial populations. As a result of the experiments conducted in this study, a particular PGA that combines a new subtour technique with a known migration approach is identified to be the best for the traveling salesman problem among the five PGAs being compared.
Open Access
A comparison of eigendecomposition for sets of correlated images at different resolutions
(Colorado State University. Libraries, 2003) Roberts, Rodney G., author; Maciejewski, Anthony A., author; Saitwal, Kishor, author; IEEE, publisher
Eigendecomposition is a common technique that is performed on sets of correlated images in a number of computer vision and robotics applications. Unfortunately, the computation of an eigendecomposition can become prohibitively expensive when dealing with very high resolution images. While reducing the resolution of the images will reduce the computational expense, it is not known how this will affect the quality of the resulting eigendecomposition. The work presented here proposes a framework for quantifying the effects of varying the resolution of images on the eigendecomposition that is computed from those images. Preliminary results show that an eigendecomposition from low-resolution images may be nearly as effective in some applications as those from high-resolution images.
Open Access
A comparison of two methods for choosing repeatable control strategies for kinematically redundant manipulators
(Colorado State University. Libraries, 1992) Maciejewski, Anthony A., author; Roberts, Rodney G., author; IEEE, publisher
A kinematically redundant manipulator is a robotic system that has more than the minimum number of degrees of freedom that are required for a specified task. Due to this additional freedom, control strategies may yield solutions which are not repeatable in the sense that the manipulator may not return to its initial joint configuration for closed end effector paths. This paper presents two methods for choosing repeatable control strategies which minimize their distance from a non-repeatable inverse with desirable properties. The first method minimizes the integral norm of the difference of the desired inverse and a repeatable inverse. While this is the more appropriate criterion, it results in a difficult optimization. The second method, which minimizes the distance of the null vectors associated with the desired and the repeatable inverses, is somewhat easier to implement. As an illustrative example the pseudoinverse is approximated in a region of the joint space using both techniques.
Open Access
A computational feasibility study of failure-tolerant path planning
(Colorado State University. Libraries, 2004) Maciejewski, Anthony A., author; Jamisola, Rodrigo S., author; Roberts, Rodney G., author; American Nuclear Society, publisher
This work considers the computational costs associated with the implementation of a failure-tolerant path planning algorithm proposed in [1]. The algorithm makes the following assumptions: a manipulator is redundant relative to its task, only a single joint failure occurs at any given time, the manipulator is capable of detecting a joint failure and immediately locks the failed joint, and the environment is static and known. The algorithm is evaluated on a three degree-of-freedom planar manipulator for a total of eleven thousand different scenarios, randomly varying the robot's start and goal positions and the number and locations of obstacles in the environment. Statistical data are presented related to the computation time required by the different steps of the algorithm as a function of the complexity of the environment.
Open Access
A data-driven approach for maximizing available wind energy through a dedicated pricing mechanism for charging residential plug-in electric vehicles
(Colorado State University. Libraries, 2019) Eldali, Fathalla, author; Suryanarayanan, Siddharth, advisor; Collins, George J., committee member; Zimmerle, Dan, committee member; Abdel-Ghany, Salah, committee member
Wind energy generation is growing significantly because of its favorable attributes such as cost-effectiveness and environment-friendliness. Electricity is the most perishable commodity as it must be consumed almost instantaneously as it is produced. Because of that, the variable nature of wind power generation and the challenges in forecasting the output power of wind impose problems of curtailment (excess of available wind energy than forecast) and deployment of reserves (deficit of available wind energy than forecast). Energy storage for wind power installations is a potential solution; however, storing large amounts of energy over long time periods is an expensive and inefficient solution. Plug-in electric vehicles (PEVs) are recognized as one of the assets to integrate energy storage on the distribution side of the electricity grid. Thus, PEVs charging presents an alternative solution for managing this excess energy in wind energy-rich grids. An accurate wind power forecasting (WPF) in the day-ahead market leads to a more predictable dispatch and unit-commitment (UC) of generators, thus reducing the need for reserves and storage. Typically, reserves to match the imbalance in supply and demand of electricity are provided by generators that are more expensive than the ones engaged in primary services. Markets in different regions of the world have specific designs, operation policies, and regulations when it comes to variable sources (e.g., wind, and solar). Independent system operators (ISOs), tasked with handling electricity markets in the US, must meet regulating reserve as directed by the North America Electric Reliability Council (NERC). One of these requirements is that the sufficient reserve must be available to cover the generation deficit. This deficit can be due to under-forecasting. There is also a case when ISOs need to curtail wind energy generation because of over-forecasting. In the first part of this dissertation, wind power data from the Electric Reliability Council of Texas (ERCOT) market is used to improve WPF as Texas has the highest installed wind energy capacity in the North American electricity grid. Autoregressive integrated moving average (ARIMA) model is used for WPF improvement. There is also a need to develop a coherent metric to quantify the improvements to WPF because different studies use different metrics. Also, using the statistical representation of the reduction in error does not necessarily reflect the overall benefit, especially the economic benefit, for ISOs. In the second part of this dissertation work, modifications of on risk-adjusted metrics used in investments assessments are developed and applied to the operation cost (OC). OC is the result of running the economic dispatch (ED) on realistic synthetic models of the actual Texas grid to evaluate the impact of the WPF improvement on the cost of operation. The modifications of the above-mentioned risk-adjusted metrics are also applied to deferring the capital investment on the distribution systems. Then, the metrics are used to assess the combination of photovoltaic (PV) and battery energy storage system (BESS) at the residential section of the distribution grid as explained in appendix A. The third part of this dissertation uses a data-driven approach to investigate existing pricing mechanisms for a Texan city (i.e., Austin) located in a wind energy-rich grid such as ERCOT with an increased adoption rate of PEVs. The study performed indicates the need for an alternative dynamic pricing mechanism dedicated to PEVs than the existing choices for maximizing the utility of available energy from wind in the absence of grid-level energy storage. Dynamic pricing produces an opportunity to avoid high costs for the power provider and benefits the consumers if they respond to the change of the price. However, achieving these benefits needs smart rate design and real data. After justifying the need for fair pricing mechanisms to benefit the utility and the customers for the coordination of wind energy and PEVs charging in wind energy-rich grid, this dissertation designs a time-varying pricing mechanism. This dissertation employs a data decomposition technique to design a dedicated pricing mechanism for PEVs. We use real data of a city with high projections of PEVs (Austin, Texas) located in a wind-rich electricity grid (ERCOT) to demonstrate this design of a dynamic pricing method.
Open Access
A description of the CSU–CHILL National Radar Facility
(Colorado State University. Libraries, 2000) Bowie, Robert K., author; Mueller, E. A., author; Chandrasekar, V., author; Rutledge, Steven A., author; Kennedy, Patrick C., author; Bringi, V. N., author; Brunkow, David, author; American Meteorological Society, publisher
The subject of this paper is the Colorado State University-University of Chicago-Illinois State Water Survey (CSU-CHILL) National Radar Facility's S-band polarimetric research radar. Key features of this system include polarization agility (provided by the dual-transmitter, dual-receiver design), a recently updated signal processor, and a low (-34 dB, two way) integrated cross-polar ratio (ICPR2) antenna system. After reviewing the technical description of the radar, the authors present a new differential reflectivity (ZDR) calibration technique and data examples collected in different polarization modes. Although the CSU-CHILL radar is transportable, it can also be operated in a dual-Doppler configuration with the CSU-Pawnee radar, an 11-cm Doppler radar system situated 48 km north of the CSU-CHILL Greeley field site. Used together, these radars provide three-dimensional kinematic and hydrometeor information in precipitating cloud systems.
Open Access
A different mirror
(Colorado State University. Libraries, 1994) Schneider, Richard P., author; Lear, Kevin L., author; Gourley, Paul L., author; IEEE, publisher
Mirrors grown in the crystalline structure ease manufacture of vertical-cavity lasers, which emit collimated circular beams and can form large two-dimensional arrays. The authors discuss the fabrication of the surface emitting laser mirrors. By means of techniques such as molecular beam epitaxy and metal-organic vapor phase epitaxy, hundreds of layers of semiconductor materials can be grown one on top of the other. By mixing and matching the materials to create "designer" alloys, it is possible to grow a crystalline structure with all the electrical and optical properties desired for its various parts. This method of tailoring semiconductor structures is called bandgap engineering. The principles of the mirrors and their applications are discussed.
Open Access
A distributed network of autonomous environmental monitoring systems
(Colorado State University. Libraries, 2018) Kinhal, Kiran Krishnamurthy, author; Azimi-Sadjadi, Mahmood R., advisor; Wilson, Jesse, committee member; Ghosh, Sudipto, committee member
Acoustic wireless sensor networks have found applications in various areas including monitoring, assisted living, home automation, security and situational awareness. The process of acoustic detection and classification usually demands significant human involvement in the form of visual and audio examination of the collected data. The accuracy of the detection and classification outcome through this process is often limited by inevitable human errors. In order to overcome this limitation and to automate this process, we present a new fully decentralized decision-making platform referred to as Environmental Monitoring Station (EMS) for sensor-level detection and classification of acoustic airborne sources in national parks. The EMS automatically reports this information to a park station through two wireless communication systems. More specifically, in this thesis, we focus on the implementation of the communication systems on the EMS, and also on the design of 1/3rd octave filter bank that is used for onboard spectral sub-band feature generation. A 1/3rd octave filter bank was implemented on the ARTIX-7 FPGA as a custom hardware unit and was interfaced with the detection and classification algorithm on the MicroBlaze softcore processor. The detection results are stored in an SD card and the source counts are tracked in the MicroBlaze firmware. The EMS board is equipped with two expansion slots for incorporating the XBee as well as GSM communication systems. The XBee modules help to build a self-forming mesh network of EMS nodes and makes it easy to add or remove nodes into the network. The GSM module is used as a gateway to send data to the web server. The EMS system is capable of performing detection, classification, and reporting of the source events in near real-time. A field test was recently conducted in the Lake Mead National Recreation Area by deploying a previously trained system as a slave node and a gateway as a master node to demonstrate and evaluate the detection and classification and the networking abilities of the developed system. It was found that the trained EMS system was able to adequately detect and classify the sources of interest and communicate the results through a gateway to the park station successfully. At the time of writing this document, only two fully functional EMS boards were built. Thus, it was not possible to physically build a mesh network of several EMS systems. Thus, future research should focus on accomplishing this task. During the field test, it was not possible to achieve a high transmission range for XBee, due to RF interference present in the deployment area. An effort needs to be made to achieve a higher transmission range for XBees by using a high gain antenna and keeping the antenna in line-of-sight as much as possible. Due to inadequate training data, the EMS system frequently misclassified the sources and mis-detected interference as sources. Thus, it is necessary to train the detection and classification algorithm by using a larger and more representative data set with considerable variability to make it more robust and less prone to variability in deployment location.
Open Access
A fast learning algorithm for Gabor transformation
(Colorado State University. Libraries, 1996) Ibrahim, Ayman, author; Azimi-Sadjadi, Mahmood R., author; IEEE, publisher
An adaptive learning approach for the computation of the coefficients of the generalized nonorthogonal 2-D Gabor transform representation is introduced in this correspondence. The algorithm uses a recursive least squares (RLS) type algorithm. The aim is to achieve minimum mean squared error for the reconstructed image from the set of the Gabor coefficients. The proposed RLS learning offers better accuracy and faster convergence behavior when compared with the least mean squares (LMS)-based algorithms. Applications of this scheme in image data reduction are also demonstrated.