## Files in this item

FilesDescriptionFormat

application/pdf

9624418.pdf (5MB)
(no description provided)PDF

## Description

 Title: A study of iterative methods on forward and inverse scattering problems Author(s): Lin, Jiun-Hwa Doctoral Committee Chair(s): Chew, Weng Cho Department / Program: Engineering, Electronics and Electrical Discipline: Engineering, Electronics and Electrical Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Engineering, Electronics and Electrical Abstract: Iterative methods are suitable for solving large-size problems in the electromagnetic and acoustic wave scattering. Both the conjugate gradient and bi-conjugate gradient methods combined with the fast Fourier transform (CGFFT and BiCGFFT) are employed as efficient solvers in forward and inverse scattering problems for penetrable bodies.In microwave imaging, material permittivity is the parameter to retrieve. The distorted Born iterative method (DBIM), a nonlinear inverse scattering algorithm that accounts for multiple scattering, can retrieve the permittivity of high contrast. The computational cost for each iteration is $O(N\sp{1.5}\ \log\ N)$ as the number of transmitters is $O(N\sp{0.5}),$ where N is the number of cells. Real experimental data has been processed by the algorithm under a full-view system to obtain images in real and imaginary parts of permittivity. With the aid of the frequency-hopping scheme, large-size objects can be reconstructed with higher fidelity.The nested equivalence principle algorithm (NEPAL) has been developed to implement the matrix-vector multiply in an O(N log N) fashion. NEPAL can also be applied in the cases of nonuniform grids. With the fast multipole method (FMM) incorporated in NEPAL, an O(N) algorithm can be achieved to perform the matrix-vector multiply.The T-matrix method is used to formulate the three-dimensional electromagnetic scattering problems. Exploiting the Toeplitz structure of the translation matrix, BiCGFFT is invoked as the solver, which requires only O(N log N) operations at each iteration and O(N) memory storage. Efficiency in computation and storage enables the algorithm to solve large problems in real practice.Acoustic wave equations possess the same features as the electromagnetic wave equations for $H\sb{z}$ polarization in two dimensions. The local shape function method (LSF) developed for inverse electromagnetic scattering is adapted to reconstructing both the density and compressibility of soft tissues in ultrasonic imaging. CGFFT is utilized as the forward solver as required to implement inverse operators. The capability of the algorithm has been demonstrated in the reconstructions from the experimental data as well as the synthetic data, and its complexity can be $O(N\sp{1.5}\ {\rm log}\ N)$ at each iteration. A multiple-frequency scheme, such as the frequency-hopping method, provides better reconstruction than a single-frequency scheme. Issue Date: 1995 Type: Text Language: English URI: http://hdl.handle.net/2142/23515 Rights Information: Copyright 1995 Lin, Jiun-Hwa Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9624418 OCLC Identifier: (UMI)AAI9624418
﻿