http://hdl.handle.net/2142/8888 Dissertations and Theses in Electrical and Computer Engineering http://hdl.handle.net/2142/11992 Incorporation of Hysteretic Effects in Model-Order Reduction Analysis of Magnetic Devices Sander, Jonathan J. The ability to predict the properties of magnetic materials in a device is essential to ensuring the correct operation and optimization of the design as well as the device behavior over a wide range of input frequencies. Typically, development and simulation of wide-bandwidth models requires detailed, physics-based simulations that utilize significant computational resources. Balancing the trade-offs between model computational overhead and accuracy can be cumbersome, especially when the nonlinear effects of saturation and hysteresis are included in the model. This study focuses on the development of a system for analyzing magnetic devices in cases where model accuracy and computational intensity must be carefully and easily balanced by the engineer. A method for adjusting model complexity and corresponding level of detail while incorporating the nonlinear effects of hysteresis is presented that builds upon recent work in loss analysis and magnetic equivalent circuit (MEC) modeling. The approach utilizes MEC models in conjunction with linearization and model-order reduction techniques to process magnetic devices based on geometry and core type. The validity of steady-state permeability approximations is also discussed. hysteresis model reduction MEC Mon, 01 Jun 2009 16:07:30 GMT http://hdl.handle.net/2142/11991 Broadband Macromodeling via a Fast Implementation of Vector Fitting with Passivity Enforcement Goh, Patrick Kuanlye As operating frequencies and signal speeds continue to increase in modern devices, the effects of packages and interconnects on the overall signal integrity become increasingly important. The complex electromagnetic behaviors of these often complicated structures must be characterized in order to take their effects into account. Broadband macromodeling deals with the generation of network models of these devices in order to accurately predict their behaviors in circuit simulators. This often involves the generation of passive rational function representations of the system from the measured port responses. In this thesis, we will employ the vector fitting algorithm to generate a rational function representation of the system along with its state space model. Various issues on the subject will be discussed, including the recently developed fast fitting method for multiport devices. Passivity of the model, which is one of the most prominent issues on the subject, will be addressed. A robust algorithm, via residue perturbation, to enforce passivity in nonpassive models will be presented. Finally, numerical results will be presented to demonstrate the performance of the overall process. Macromodeling Vector Fitting Passivity Mon, 01 Jun 2009 16:07:29 GMT http://hdl.handle.net/2142/11990 Shape Approximation of Printed Images in VLSI Design Han, Khine Despite application of optical proximity correction (OPC) and resolution enhancement techniques (RET) to improve printing, limitations in lithography and manufacturing processes still lead to undesirable irregularities in printed images on wafer. These post-lithographic distorted shapes are of interest for electrical extraction of printed circuits. To reduce processing time, it is desirable to approximate the resulting two-dimensional contours with simpler polygons. For the case of capacitance extraction algorithms, pairs of outer and inner approximate polygons, which approach the original shape with tighter error restriction, are preferable. Many existing approximation algorithms produce a single approximate polygon per shape, utilizing two main approaches: piecewise linear fit with a fixed number of segments or bounded error, and identification of subsets of dominant points in the resultant polygon. This research presents an approximation algorithm of the former approach using simple one-dimensional methods to efficiently approximate two-dimensional closed shapes by pairs of outer and inner polygons. Each input shape is first decomposed using a greedy strategy into a set of connected functions; the set size is assumed to be small compared to the input size, and each function is assigned an x or y approximation direction. Each decomposed function is approximated with an optimal number of subdivision points within a certain bounded error restricted to one particular assigned direction; the upper- and lower-bound vertices associated with each subdivision are also calculated. A decision method is employed to determine the relative locations of the outer and inner regions of the two-dimensional curve, the results are pieced together to generate the complete outer and inner approximate polygons. The one-dimensional approach guarantees linear-time approximation of each function. Under the assumption of possible decomposition into a small set of connected functions, the total approximation time of the proposed algorithm is linear in the number of input vertices. For verification, the algorithm is applied to several test files containing either post-lithographic or arbitrary two-dimensional closed shapes for several specified bounded error values. A few techniques are also discussed for further performance improvements. vlsi polygon approximation Mon, 01 Jun 2009 16:07:27 GMT http://hdl.handle.net/2142/11989 On-Chip Voltage Controlled Oscillator for Clock Data Recovery Systems Jayaraman, Srivatsan As the clock rates of microprocessors keep increasing, high data rate input/output (IO) should be designed to realize their maximum benefit. However, designing robust, low power, high speed IO links is very challenging due to the increased transmission line loss, cross talk, and signal distortion resulting in intersymbol interference. Synchronous sampling is often employed to overcome these challenges. However, synchronous sampling makes use of a high purity oscillator to minimize the clock jitter. This thesis focuses on the design of a high purity, low power, voltage controlled oscillator to be used as part of the clock data recovery system in a 25 Gb/s serial IO link. Voltage controlled oscillator Differential oscillator Mon, 01 Jun 2009 16:07:25 GMT http://hdl.handle.net/2142/11988 Dynamic-Data Driven Real-Time Identification for Electric Power Systems Liu, Shanshan Power system engineers face a double challenge: to operate electric power systems within narrow stability and security margins, and to maintain high reliability. There is an acute need to better understand the dynamic nature of power systems in order to be prepared for critical situations as they arise. Innovative measurement tools, such as phasor measurement units, can capture not only the slow variation of the voltages and currents but also the underlying oscillations in a power system. Such dynamic data accessibility provides us a strong motivation and a useful tool to explore dynamic-data driven applications in power systems. To fulfill this goal, this dissertation focuses on the following three areas: Developing accurate dynamic load models and updating variable parameters based on the measurement data, applying advanced nonlinear filtering concepts and technologies to real-time identification of power system models, and addressing computational issues by implementing the balanced truncation method. By obtaining more realistic system models, together with timely updated parameters and stochastic influence consideration, we can have an accurate portrait of the ongoing phenomena in an electrical power system. Hence we can further improve state estimation, stability analysis and real-time operation. Load Modeling, Nonlinear Filtering, State Estimation, Order Reduction, Balanced Truncation Mon, 01 Jun 2009 16:05:27 GMT http://hdl.handle.net/2142/11987 Efficient Finite Element Electromagnetic Analysis for High-Frequency/High-Speed Circuits And Multiconductor Transmission Lines Lee, Shih-hao This dissertation comprises the following four components. (1) Development of a robust and efficient 3-D finite element electromagnetic field solver with high-order vector elements for high-frequency and high-speed circuit simulations. The solver supports wave port and lumped port excitations as well as the incorporation of lumped networks and circuit models in a distributed finite element model. An adaptive multipoint model order reduction method is developed for fast broadband analysis. (2) Development of a fast and accurate multiconductor transmission line simulator and parameter extractor with improved model order reduction techniques. A methodology is further proposed for a combined quasi-TEM and full-wave transmission line analysis, which possesses their respective advantages and ensures full-wave accuracy from DC to very high frequencies. The transmission line analysis also takes into account the frequency dependence of dielectric materials. (3) Study of the low-frequency instability problem in the 3-D full-wave finite element simulation. The tree-cotree splitting is combined with several other techniques to improve the matrix conditioning and extend full-wave solutions down to very low frequencies for a more robust broadband characterization of high-speed digital circuits. (4) A combined domain decomposition–model order reduction (DD–MOR) method for efficient full-wave analysis of interconnections in multilayer printed circuit boards. The method not only brings a significant enhancement to computational efficiency while maintaining full-wave accuracy, but also provides great flexibility in the finite element mesh generation. electromagnetics microwave finite element method fem nodal elements vector elements edge elements higher-order elements triangular elements tetrahedral elements finite element analysis full-wave analysis impedance boundary condition port boundary condition wave port lumped port deembedding thin-wire approximation thin wire modeling internal impedance lumped elements lumped circuits field-circuit simulation EM-circuit simulation stamping reduced-order modeling model order reduction MOR fast frequency sweep solution space projection SSP quasi-static analysis quasi-TEM analysis generalized eigenproblem Lanczos algorithm modal analysis eigenanalysis frequency-dependent media anisotropic media Debye model multiconductor transmission lines transmission line parameters frequency-dependent losses conductor loss dielectric loss substrate loss characteristic impedance skin effect proximity effect parameter extraction resistance inductance capacitance conductance per-unit-length composite conductors waveguide filter coplanar waveguide CPW striplines microstrip lines high-frequency circuits RF circuits high-speed circuits tree-cotree splitting low-frequency breakdown low-frequency instability preconditioning bonding wire printed circuit board multilayer PCB via-holes signal integrity electromagnetic coupling interconnects domain decomposition approximate modal interface AMI AMI–SSP DD–MOR CAD Mon, 01 Jun 2009 16:05:25 GMT http://hdl.handle.net/2142/11986 Parallel Plasma Field Directed Sputter Sharpening of Field Emitters Lee, Eric D. Many of the current methods to sharpen field emitters are time consuming and can only process one field emitter at a time. In this thesis, a method is proposed to parallel process multiple field emitters using a DC glow discharge plasma as the ion source in conjunction with field directed sputter sharpening methodology. With field directed sputter sharpening, a positive voltage bias is applied to the field emitter and impinging ions are repelled away from the apex of the tip to the shank of the tip. This produces a very sharp tip with radius of curvature of approximately 1 nm. A plasma system was designed and built, and tungsten tips for use in scanning tunneling microscopy (STM) applications were sputtered with argon ions. The result is that as the tip voltage bias to plasma voltage bias ratio is increased above approximately 0.1, the cone angle of the tungsten tip decreases. The radius of curvature of the tip also decreases, but the result is not always consistent and does not reach the same order of magnitude as the result achieved by field directed sputter sharpening with an ion gun. This result shows much promise and further work is necessary to refine the process and achieve consistent results. Sputter Sharpening, Plasma, Field Emitters Mon, 01 Jun 2009 16:05:24 GMT http://hdl.handle.net/2142/11985 Quantification of Ultrasound Contrast Agents Using High-Frequency Ultrasound Ma, Darryl C. Ultrasound contrast agents (UCAs) are small microbubbles filled with gas. Because of their scattering properties, UCAs enhance the diagnostic capabilities of ultrasonic imaging. UCAs are associated with therapeutic or enhancing therapeutic applications of ultrasound and with possible adverse bioeffects. Quantification of the in vivo concentration of microbubbles is therefore essential to establishing a dose/effect response for therapeutics and for quantifying other bioeffects. The concentration of UCAs is hypothesized to be proportional to the magnitude of the ultrasonic backscattered power spectrum. To demonstrate the ability to quantify UCAs from ultrasonic backscatter, several experiments were conducted. All experiments were conducted with FDA approved Definity® contrast agents and were performed in vitro, i.e., within a beaker or within a perfusion phantom, or in vivo, i.e., within the auricular artery of a rabbit. Estimates of the UCA concentration were obtained by comparing estimates of the backscattered power spectrum corresponding to the scattering from UCAs. A Monte Carlo technique was used to estimate the UCA concentration in vitro by minimizing the mean square error between the estimated power spectrum and the theoretical power spectrum. Samples of the Definity mixture were also extracted and analyzed under a fluorescence microscope and hemacytometer to obtain the size distribution and concentration of microbubbles optically for comparison with the ultrasound estimates. In both the in vitro and in vivo experiments, the linear relationship between the UCA concentration and magnitude of the ultrasonic backscattered power spectrum was demonstrated. Additionally, with the Monte Carlo technique, the UCA concentration and mean microbubble radius was estimated to within 12.3% and 8.48% of the optically measured values, respectively. UCAs Ultrasound Contrast Agents Backscatter Cross Section Definity Bioacoustics Quantification In Vivo rabbit experiments Mon, 01 Jun 2009 16:05:22 GMT http://hdl.handle.net/2142/11984 Improved Techniques for Statistical Analysis of the Envelope of Backscattered Ultrasound Using the Homodyned K Distribution Hruska, David P. Biomedical ultrasound is a prominent imaging modality for diagnostics. Conventional ultrasonic imaging is qualitative in nature with spatial resolution up to hundreds of micrometers. Quantitative ultrasound techniques based on ultrasonic backscatter can provide estimates describing tissue microstructure. Improving quantitative ultrasound techniques will result in improved diagnostic capabilities of ultrasound. Quantitative techniques were developed and assessed based on the envelope of backscattered ultrasound. The envelope of backscattered ultrasound can be modeled as the superposition of the scattered signals from individual scatterers in the medium being interrogated. As such, the envelope signal is statistical in nature. By applying a model to the amplitude distribution of the envelope, information about the sub-resolution material properties such as the scatterer number density and organizational structure can be obtained. The homodyned K distribution was used to model the envelope of backscattered ultrasound. An efficient parameter estimation algorithm was developed and tested through simulations and experiments. Techniques to reduce estimate bias and variance were assessed. The diagnostic potential of tissue characterization based on envelope statistics was evaluated. Ultrasonic tissue characterization ultrasound backscatter envelope statistics homodyned K distribution Mon, 01 Jun 2009 16:05:20 GMT http://hdl.handle.net/2142/11983 Transient Phase-Change Effect in Phase-Change Memory Devices Yeo, Eng Guan Phase-change random access memory (PCRAM) is one of the next-generation memories with the most potential due to its many good characteristics, such as nonvolatility, high endurance and long data retention. PCRAM has the potential to replace flash memory, which has limited durability and speed. PCRAM is based on phase change from a high-resistance amorphous state to a low-resistance crystalline state and vice versa in nanosecond timescale. However, the mechanism by which phase change occurs is still unknown. This work introduces a transient electrical method to relate the phase change phenomenon to the mechanism behind it. In this thesis, PCRAM devices were fabricated with Ge2Sb2Te5 (GST) and AgInSbTe, which are well known nucleation and growth dominated phase change materials. The transient electrical waveform during crystallization was identified as a method to characterize the phase change phenomenon in the device and provide a link to the mechanism behind the phase change effect. Two time periods, delay time and current recovery time, were discovered during this transient electric analysis, which relate to nucleation and growth of the phase change material. This method could potentially be used across different device structures and phase change materials to identify their effect on the phase change mechanism. phase-change transient effect PCRAM Mon, 01 Jun 2009 16:05:18 GMT