1,450 research outputs found
Low-frequency model-order reduction of electromagnetic fields without matrix factorization
No full textElectrical Engineering, Mathematics and Computer Scienc
Dr. Shanesha R.F. Brooks-Tatum, RWWL AUC, July 2011
No full textThis video is a conversation with Dr. Shanesha R.F. Brooks-Tatum. Dr. Brooks-Tatum talks about her book, "The Encyclopedia of Hip Hop Literature." Daniel Le, AUC Woodruff Library, is the interviewer
Accurate Electromagnetic Modeling Methods for Integrated Circuits
No full textThe present development of modern integrated circuits (IC’s) is characterized by a number of critical factors that make their design and verification considerably more difficult than before. This dissertation addresses the important questions of modeling all electromagnetic behavior of features on the chip, efficient methods to solve large systems of equations and Model Order Reduction techniques in layout-to-circuit extraction. More specifically, it covers the following issues: \u95 The Surface Integrated Field Equations Method which solves, in an unified framework and even for difficult high contrast situations, the static and stationary electric and magnetic field problems and the electromagnetic field problems in both time and frequency domain. \u95 The Hierarchically Semi-separable theory that is based on exploiting structural properties of sub-matrices of the original. \u95 The Mult-Level Hierarchical Schur Algorithm which succeeds in reducing the computational complexity while computing an accurate estimation to the values of the neglected capacitances in 3D layout-to-circuit extraction.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Reduced-order modeling of transient electromagnetic fields
No full textElectrical Engineering, Mathematics and Computer Scienc
Letter: R.F. Pettigrew to H.L. Loucks, May 30, 1916
No full textR.F. Pettigrew articulates to H.L. Loucks his distaste for the book that Loucks recommended to him. Pettigrew also mentions that he would prefer to remain distanced from any conference with the author of the book. Pettigrew expresses great admiration and interest in Loucks' manuscript and desire to read it further
Dielectric Shimming: Optimization Techniques for Dielectric Pads in MRI
No full textDielectric shimming is proven to be very useful in increasing the homogeneity of the 1+ field in high field MRI. Current optimization and design techniques for dielectric pad parameters are slow. The goal of this thesis is to find a fast and accurate pad design and optimization technique. Two new techniques are proposed. The first, a method that simply uses inspection by solving the forward problem in a relatively fast way. The other proposed technique follows a more analytical approach to find the optimal permittivity and conductivity of a pad in a couple of iterative steps with a Gauss-Newton method. This last technique uses a new proposed approach to predict the phase of the 1+ field in a direct fashion. These techniques provide fast and accurate simulation results for a two-dimensional abdominal body slice placed in a 3T MRI scanner for different pad scenarios. From these results it can be concluded that both proposed techniques generate comparable pads, which are able to increase the homogeneity of the 1+ field. A comparison between the two techniques is made. The Gauss-Newton method provides a fast, robust and accurate optimization technique for large scale problems, but offers less flexibility and insight to the data compared to the method via inspection. The flexibility of the method via inspection and the insight it provides is shown for different scenarios (pad location, multiple pads, pad shape, pad thickness), where the effect of the optimal permittivity and conductivity on the homogeneity of the resulting 1+ field is simulated. Even the maximum allowed SAR can be incorporated in this pad optimization technique.Electrical Engineering, Mathematics and Computer ScienceMicroelectronicsCircuits and System
Imaging of Cracks and Weak Spots in Steel and Aluminium Plate Rolls
No full textBecause of several - sometimes extreme - complications caused by cracks and weak spots in a metal industry roll, it is of great importance to detect these defects in time. Measurements on rolls with artificial- and natural defects have been performed. An imaging operator is introduced, which uses the measurement data to depict the correct locations of the scatterers in the roll. Even when almost 95% of the original measurement data is discarded, the defects in the roll can still be detected. This thesis shows how these imperfections cause deviations in the eddy current measurement setup and presents how the deviations can be used to locate these defects in the steel. The roll is modeled as a conductive half space after which the inhomogeneous Helmholtz equation will be solved to find the electromagnetic fields inside the steel. Defects are modeled as small spheroids with respect to the wavelength, which makes it possible to find the fields inside these scatterers. Furthermore, an equation is found which relates deviations in receiver signals to the electric- and magnetic fields and contrasts in the roll. The quasi-static approach is used to simplify this equation, after which results are shown for different defects and antenna configurations. Similar outcomes are obtained when the measurement data is compared to the theory.Circuits and SystemsTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Generalized Signal Models and Direct FID-Based Dielectric Parameter Retrieval in MRI
No full textIn this article, we present full-wave signal models for magnetic and electric field measurements in magnetic resonance imaging (MRI). Our analysis is based on a scattering formalism in which the presence of an object or body is taken into account via an electric scattering source. We show that these signal models can be evaluated, provided that Green's tensors of the background field are known along with the dielectric parameters of the object and the magnetization within the excited part of the object. Furthermore, explicit signal expressions are derived in the case of a small homogeneous ball that is embedded in free space and for which the quasi-static Born approximation can be applied. The conductivity and permittivity of the ball appear as explicit parameters in the resulting signal models and allow us to study the sensitivity of the measured signals with respect to these dielectric parameters. Moreover, for free induction decay signals, we show through simulations that, under certain conditions, it is possible to retrieve the dielectric parameters of the ball from noise-contaminated induction decay signals that are based on electric or magnetic field measurements. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
A Krylov Subspace Approach to Parametric Inversion of Electromagnetic Data Based on Residual Minimization
No full textIn this thesis we present a Krylov subspace technique and use residual minimization to efficiently solve parametric electromagnetic inversion problems. We exploit the shift-invariance property of Krylov subspaces to compute total fields inside a homogeneous object for a whole range of contrast values. As soon as these fields are found, we can determine the corresponding scattered fields in a straightforward manner. This approach allows us to solve the inverse problem by simply inspecting an objective function which measures the discrepancy between the measured and modeled scattered field data.Inverse ScatteringLaboratory of Electromagnetic ResearchElectrical Engineering, Mathematics and Computer Scienc
Photoacoustic Imaging by Means of Sparsity Regularization
No full textThe intertwine of the optical and acoustic domains by the photoacoustic effect has given rise to the novel technique of photoacoustic imaging. As a relatively new field it faces many challenges from different character on the way to clinical applications. One of these challenges, which deteriorates image quality and sharpness, is noise. The usual answer to this undesired effect is averaging over multiple measurements. This has its cost however, prompting the search for other noise reduction methods. In this thesis, we assume our imaging domain to be sparse and apply sparsity regularization accordingly. By this, we attempt to reduce the noise artefacts and improve the overall signal-to-noise ratio. To accomplish this task, we first solve the photoacoustic wave equation in linear form and discretize the result to acquire a data model. Then, we construct an imaging procedure based on the adjoint operator. Finally, we apply the sparsity regularization procedure to both synthetic and experimental data. We report on improved signal-to-noise ratio and several interesting finds among which are the dependence of the regularization parameter on the noise power and a different optimality criterion for the parameter choice in photoacoustic imaging.Circuits and SystemsTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
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