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Cylindrical RF tomography Lam, Kim

Abstract

Tomography allows the examination of an object's interior without having to destroy the object. There have been many forms of tomography including MRIs and CT scans. All forms of tomography infer the interior of an object from a set of measurements. An algorithm to infer the features of infinite dielectric cylinders using electromagnetic waves is developed in this thesis. The intended application for this algorithm is the imaging of lumber. The algorithm recovers the dielectric permittivity distribution from an infinite cylinder. It uses Richmond's Method to model the physical behavior of the infinite cylinder. The algorithm uses an iterative non-linear inversion scheme to recover the dielectric permittivity distribution. The non-linear inversion scheme uses a regularization term that minimizes the structure of the permittivity distribution subject to a constraint involving the measured scattered field from the cylinder. It was found that by decreasing the weighting of the regularization, and eventually turning off the regularization, the exact permittivity distribution can be recovered for a noiseless and over-determined system. In the presence of noise, an approximate permittivity distribution can be recovered; however regularization cannot be turned off. Similarly, for an under-determined system, an approximate permittivity distribution can be found, but regularization cannot be turned off.

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