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dc.contributor.advisorGope, Dipanjan
dc.contributor.authorMuniganti, Harikiran
dc.date.accessioned2022-08-01T09:30:17Z
dc.date.available2022-08-01T09:30:17Z
dc.date.submitted2021
dc.identifier.urihttps://etd.iisc.ac.in/handle/2005/5807
dc.description.abstractAn inverse problem in Electromagnetics (EM) refers to the process of reconstructing the physical system by processing the measured data of its electromagnetic properties. Inverse problems are typically ill-posed, and this makes them far more challenging than the typically well-posed forward problem. The solution of such inverse problems finds applications in nondestructive testing and evaluation, biomedical imaging, geophysical exploration etc. This thesis addresses some inverse problems specific to the area of electromagnetics, arising in three different scenarios. The first problem is 3-D quantitative imaging primarily targeted towards bio-medical applications. The task is to retrieve the dielectric properties, location and the shape of an unknown object from the measured scattered field. The unknown object is modeled by discretization into several voxels, with each voxel having its own dielectric property. As the inverse problem is non-linear, typically an iterative optimization process is adopted, and a forward problem needs to be solved at every iteration. The total time for reconstruction depends on the forward solver time and the number of iterations. In many cases, the number of unknowns to be reconstructed is prohibitively large. Further, the non-convergence or false-convergence of the optimization process presents its own challenge. This thesis proposes two methodologies to solve these challenges. In the first approach a multilevel methodology is proposed where voxels are hierarchically decomposed into smaller voxels based on an appropriate indicator, leading to a non-uniform multilevel voxel structure aimed at reducing the eventual number of unknowns to be solved for, also enabling faster convergence. In the second approach, a two-stage framework is proposed comprising of Machine Learning classification followed by optimization (ML-OPT). The first stage generates an appropriate adaptive grid for the optimization process and provides a suitable initial guess aiding convergence to the global minima. This approach is aimed at detecting breast tumors where the optimization algorithm can aim for higher resolution in the suspected tumor region, while using lower resolution elsewhere. The second problem is in the domain of high-speed circuits and is focused on synthesis of transmission line physical parameters given the desired electrical parameters like characteristic impedance and propagation constant. A forward solver is used to train Neural network for several different configurations for analysis and an optimization algorithm is used for synthesis. The third problem is focused on finding the source of radiation in an electronic system e.g. an automotive ECU, given the measured field at the antenna in the radiated emissions setup. The source of radiation can be from common mode current on the cable harness or from the Design Under Test (DUT). A method based on Huygens box is proposed to quantify the radiation from cable and DUT at each frequency. On each cell of the Huygens box the value of electric field computed at the observation point taking the Electric Current (J) and Magnetic Current (M) on that cell as sources and this information on the Huygens box is used to quantify the radiation. Some part of the presented work is used via technology-transfer at Simyog Technology Pvt. Ltd., an IISc incubated startup, to develop a simulation software called Compliance-scope which allows the hardware designer to predict the EMI/EMC performance of electronics modules from an early design stage.en_US
dc.language.isoen_USen_US
dc.rightsI grant Indian Institute of Science the right to archive and to make available my thesis or dissertation in whole or in part in all forms of media, now hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertationen_US
dc.subjectInverse Problemsen_US
dc.subjectComputational Electromagenticsen_US
dc.subjectElectric Field Integral Equationen_US
dc.subjectMachine Learningen_US
dc.subjectVolume Surface Integral Equationen_US
dc.subjectLevenberg-Marquardten_US
dc.subjectElectromagnetic Interferenceen_US
dc.subjectElectromagnetic Compatibilityen_US
dc.subjectBulk Current Injectionen_US
dc.subjectMethod of Momentsen_US
dc.subjectFinite Element Methoden_US
dc.subjectFinite Difference Time Domainen_US
dc.subjectMulti-Level Fast Multipoleen_US
dc.subjectFast Fourier Transformen_US
dc.subjectRadar Cross Sectionen_US
dc.subjectGauss-Newtonen_US
dc.subjectNeural Networken_US
dc.subjectRadiated Immunityen_US
dc.subjectVector Network Analyzeren_US
dc.subject.classificationResearch Subject Categories::TECHNOLOGY::Electrical engineering, electronics and photonics::Electronicsen_US
dc.titleInverse Problems in 3D Full-wave Electromagneticsen_US
dc.typeThesisen_US
dc.degree.namePhDen_US
dc.degree.levelDoctoralen_US
dc.degree.grantorIndian Institute of Scienceen_US
dc.degree.disciplineEngineeringen_US


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