Thumbnail
Access Restriction
Open

Researcher Vinu, Thomas
Advisor Dr.Mathew, K T
Source CUSAT-Thesis
Content type Text
Educational Degree Doctor of Philosophy (Ph.D.)
File Format PDF
Language English
Subject Domain (in DDC) Technology
Subject Keyword Multiscaled frequency hopping ♦ symmetry formulation ♦ Monochromatic inverse scattering ♦ Dielectric Polarization
Abstract Electromagnetic tomography has been applied to problems innondestructive evolution, ground-penetrating radar, synthetic apertureradar, target identification, electrical well logging, medical imagingetc. The problem of electromagnetic tomography involves theestimation of cross sectional distribution dielectric permittivity,conductivity etc based on measurement of the scattered fields. Theinverse scattering problem of electromagnetic imaging is highly nonlinear and ill posed, and is liable to get trapped in local minima. Theiterative solution techniques employed for computing the inversescattering problem of electromagnetic imaging are highly computationintensive. Thus the solution to electromagnetic imaging problem isbeset with convergence and computational issues. The attempt of thisthesis is to develop methods suitable for improving the convergenceand reduce the total computations for tomographic imaging of twodimensional dielectric cylinders illuminated by TM polarized waves,where the scattering problem is defmed using scalar equations. A multiresolution frequency hopping approach was proposed as opposed tothe conventional frequency hopping approach employed to image largeinhomogeneous scatterers. The strategy was tested on both syntheticand experimental data and gave results that were better localized andalso accelerated the iterative procedure employed for the imaging. ADegree of Symmetry formulation was introduced to locate the scattererin the investigation domain when the scatterer cross section wascircular. The investigation domain could thus be reduced whichreduced the degrees of freedom of the inverse scattering process. Thusthe entire measured scattered data was available for the optimization offewer numbers of pixels. This resulted in better and more robust reconstructions of the scatterer cross sectional profile. The Degree ofSymmetry formulation could also be applied to the practical problemof limited angle tomography, as in the case of a buried pipeline, wherethe ill posedness is much larger. The formulation was also testedusing experimental data generated from an experimental setup that wasdesigned. The experimental results confirmed the practicalapplicability of the formulation.
Education Level UG and PG
Learning Resource Type Thesis
Publisher Institution Cochin University of Science & Technology