http://smartech.gatech.edu/handle/1853/5989 Original work by students in the School of Electrical and Computer Engineering Search the Channel search http://smartech.gatech.edu/simple-search http://smartech.gatech.edu/handle/1853/29778 Title: Hardness assurance testing and radiation hardening by design techniques for silicon-germanium heterojunction bipolar transistors and digital logic circuits <br/> <br/>Authors: Sutton, Akil Khamisi <br/> <br/>Abstract: Hydrocarbon exploration, global navigation satellite systems, computed tomography, and aircraft avionics are just a few examples of applications that require system operation at an ambient temperature, pressure, or radiation level outside the range covered by military specifications. The electronics employed in these applications are known as "extreme environment electronics." On account of the increased cost resulting from both process modifications and the use of exotic substrate materials, only a handful of semiconductor foundries have specialized in the production of extreme environment electronics. Protection of these electronic systems in an extreme environment may be attained by encapsulating sensitive circuits in a controlled environment, which provides isolation from the hostile ambient, often at a significant cost and performance penalty. In a significant departure from this traditional approach, system designers have begun to use commercial off-the-shelf technology platforms with built in mitigation techniques for extreme environment applications. Such an approach simultaneously leverages the state of the art in technology performance with significant savings in project cost. Silicon-germanium is one such commercial technology platform that demonstrates potential for deployment into extreme environment applications as a result of its excellent performance at cryogenic temperatures, remarkable tolerance to radiation-induced degradation, and monolithic integration with silicon-based manufacturing. In this dissertation the radiation response of silicon-germanium technology is investigated, and novel transistor-level layout-based techniques are implemented to improve the radiation tolerance of HBT digital logic. http://smartech.gatech.edu/handle/1853/29776 Title: Mpeg-4 avc traffic analysis and bandwidth prediction for broadband cable networks <br/> <br/>Authors: Lanfranchi, Laetitia I. <br/> <br/>Abstract: In this thesis, we analyze the bandwidth requirements of MPEG-4 AVC video traffic and then propose and evaluate the accuracy of new MPEG-4 AVC video traffic models. First, we analyze the bandwidth requirements of the videos by comparing the statistical characteristics of the different frame types. We analyze their coefficient of variability, autocorrelation, and crosscorrelation in both short and long term. The Hurst parameter is also used to investigate the long range dependence of the video traces. We then provide an insight into B-frame dropping and its impact on the statistical characteristics of the video trace. This leads us to design two algorithms that predict the size of the B-frame and the size of the group of pictures (GOP) in the short-term. To evaluate the accuracy of the prediction, a model for the error is proposed. In a broadband cable network, B-frame size prediction can be employed by a cable headend to provision video bandwidth efficiently or more importantly, reduce bit rate variability and bandwidth requirements via selective B-frame dropping, thereby minimizing buffering requirements and packet losses at the set top box. It will be shown that the model provides highly accurate prediction, in particular for movies encoded in high quality resolution. The GOP size prediction can be used to provision bandwidth. We then enhance the B-frame and GOP size prediction models using a new scene change detector metric. Finally, we design an algorithm that predicts the size of different frame types in the long-term. Clearly, a long-term prediction algorithm may suffer degraded prediction accuracy and the higher complexity may result in higher latency. However, this is offset by the additional time available for long-term prediction and the need to forecast bandwidth usage well ahead of time in order to minimize packet losses during periods of peak bandwidth demands. We also analyze the impact of the video quality and the video standard on the accuracy of the model. http://smartech.gatech.edu/handle/1853/29772 Title: A novel method for incorporating periodic boundaries into the fdtd method and the application to the study of structural color of insects <br/> <br/>Authors: Lee, Richard Todd <br/> <br/>Abstract: In this research, a new technique for modeling periodic structures in the finite-difference time-domain (FDTD) method is developed, and the technique is applied to the study of structural color in insects. Various recent supplements to the FDTD method, such as a nearly-perfect plane-wave injector and convolutional perfectly matched layer boundary condition, are used. A method for implementing the FDTD method on a parallel, distributed-memory computer cluster is given. To model a periodic structure, a single periodic cell is terminated by periodic boundary conditions (PBCs). A new technique for incorporating PBCs into the FDTD method is presented. The simplest version of the technique is limited to two-dimensional, singly-periodic geometries. The accuracy is demonstrated by comparing to independent results calculated with a frequency-domain, mode-matching method. The periodic FDTD method is then extended to the more general case of three-dimensional, doubly-periodic problems. This extension requires additional steps and imposes new limitations. The computational cost and limitations of the method are presented. Certain species of butterflies exhibit structural color, which is caused by quasi-periodic structures on the scales covering the wings. Numerical experiments are performed to develop a technique for modeling quasi-periodic structures using the periodic FDTD method. The observed structural color of butterflies is then calculated from the electromagnetic data using colorimetric theory. Three types of butterflies are considered. The first type are from the Morpho genus. These are typically a brilliant, almost metallic, blue color. The second type is the Troides magellanus, which exhibits an interplay of structural and pigmentary color, but the structural color is only visible near grazing incidence. The final type is the Ancyluris meliboeus, which exhibits iridescence on the ventral side. For all cases, the effects of changing the dimensions of various structural elements are considered. Finally, some earlier work on the design of TEM horn antennas is presented. The TEM horn is a simple and popular antenna, but only limited design information is available in the literature. A parametric study was performed, and the results are given. A complete derivation of the characteristic impedance of the basic antenna is also presented. http://smartech.gatech.edu/handle/1853/29766 Title: One-sided ultrasonic determination of third order elastic constants using angle-beam acoustoelasticity measurements <br/> <br/>Authors: Muir, Dave D. <br/> <br/>Abstract: This thesis describes procedures and theory for a family of one-sided ultrasonic methods for determining third order elastic constants (TOEC) using sets of angle-beam wedges mounted on one side of a specimen. The methods are based on the well-known acoustoelastic effect, which is the change of wave speed with applied loads and is a consequence of the mechanical nonlinearity of a material. Increases in material nonlinearity have been correlated to the progression of damage, indicating that tracking changes in TOECs may provide a practical means of monitoring damage accumulation at the microstructural level prior to formation of macroscopic defects. Ultrasonic methods are one of the only ways to measure TOECs, and most prior techniques have utilized wave propagation paths parallel and perpendicular to the loading directions. A few additional ultrasonic techniques reported in the literature have employed oblique paths but with immersion coupling. These reported techniques are generally unsuitable for field implementation. The one-sided contact approach described here is applicable for in situ measurements of TOECs and thus lays the foundation for tracking of TOECs with damage. Theory is reviewed and further developed for calculating predicted velocity changes, and thus time shifts, as a function of uniaxial tensile loading for longitudinal, shear vertical, and shear horizontal waves in the context of angle-beam transducers mounted on the surface of the specimen. A comparison is made to published results where possible. The inverse problem of determining the three TOECs of an isotropic material from three measurements employing three different angle beam configurations is comprehensively analyzed. Four configurations providing well-posed solutions are identified and examined. A detailed sensitivity analysis is carried out to identify the best mounting configuration, wave mode combinations, refracted angles and geometry requirements for recovering the three TOECs. Two transducer mounting configurations are considered: (1) attached (glued-on) transducers potentially suitable for in situ monitoring, and (2) floating (oil-coupled) transducers potentially suitable for single measurements. Limited experimental results are presented for the attached case using two longitudinal measurements and one shear vertical measurement. The floating case experiments utilized three of the four well-posed solutions, and measurements were made on several aluminum alloys and low carbon steel. Key experimental issues are identified and discussed for both transducer mounting configurations.