Home About us Contact
|
Home About us Contact | ||
|
|
||
Scattered Field (scattered + field)
Selected AbstractsSolving inverse electromagnetic problems using FDTD and gradient-based minimizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2006Erik Abenius Abstract We address time-domain inverse electromagnetic scattering for determining unknown characteristics of an object from observations of the scattered field. Applications include non-destructive characterization of media and optimization of material properties, for example, the design of radar absorbing materials. Another application is model reduction where a detailed model of a complex geometry is reduced to a simplified model. The inverse problem is formulated as an optimal control problem where the cost function to be minimized is the difference between the estimated and observed fields, and the control parameters are the unknown object characteristics. The problem is solved in a deterministic gradient-based optimization algorithm using a parallel 2D FDTD scheme. Highly accurate analytical gradients are computed from the adjoint formulation. The inverse method is applied to the characterization of layered dispersive media and the determination of parameters in subcell models for thin sheets and narrow slots. Copyright © 2006 John Wiley & Sons, Ltd. [source] Image reconstruction for a partially immersed imperfectly conducting cylinder by genetic algorithmINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 4 2009Wei Chien Abstract This article presents a computational approach to the imaging of a partially immersed imperfectly conducting cylinder. An imperfectly conducting cylinder of unknown shape and conductivity scatters the incident transverse magnetic (TM) wave in free space while the scattered field is recorded outside. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations, and the inverse scattering problem are reformulated into an optimization problem. We use genetic algorithm (GA) to reconstruct the shape and the conductivity of a partially immersed imperfectly conducting cylinder. The genetic algorithm is then used to find out the global extreme solution of the cost function. Numerical results demonstrated that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In such a case, the gradient-based methods often get trapped in a local extreme. In addition, the effect of random noise on the reconstruction is investigated. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 299,305, 2009 [source] Image reconstruction of a buried perfectly conducting cylinder illuminated by transverse electric wavesINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 6 2005Yueh-Cheng Chen Abstract This article presents a computational approach to the image reconstruction of a perfectly conducting cylinder illuminated by transverse electric waves. A perfectly conducting cylinder of unknown shape buried in one half-space and scatters the incident wave from another half-space where the scattered field is recorded. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations is derived, and the imaging problem is reformulated into an optimization problem. The steady state genetic algorithm is then employed to find out the global extreme solution of the cost function. Numerical results demonstrated that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In such a case, the gradient-based methods often get trapped in a local extreme. In addition, the effect of different noise on the reconstruction is investigated. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 261,265, 2005 [source] Image reconstruction of buried inhomogeneous dielectric cylinders coated on a conductorINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 3 2005Chun Jen Lin Abstract The image reconstruction of buried inhomogeneous dielectric cylinders coated on a conductor with known cross-section is investigated. Inhomogeneous dielectric cylinders coated on a conductor is buried in one half space and scatter a group of unrelated waves incident from another half space, where the scattered field is recorded. By proper arrangement of the various unrelated incident fields, the difficulties of ill-posedness and nonlinearity are circumvented, and the permittivity distribution can be reconstructed through simple matrix operations. The algorithm is based on the moment method and the unrelated illumination method. Numerical results show that good reconstruction has been obtained both with and without Gaussian noise in measured data. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 172,177, 2005 [source] The singular sources method for cracksMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2007Morteza Fotouhi Abstract The singular sources method is given to detect the shape of a thin infinitely cylindrical obstacle from a knowledge of the TM-polarized scattered electromagnetic field in large distance. The basic idea is based on the singular behaviour of the scattered field of the incident point source on the cross-section of the cylinder. We assume that the scatterer is a perfect conductor which is possibly coated by a material and investigate two models with different boundary conditions. Also we give a uniqueness proof for the shape reconstruction. Copyright © 2006 John Wiley & Sons, Ltd. [source] Integral equation methods for scattering by infinite rough surfacesMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 6 2003Bo Zhang Abstract In this paper, we consider the Dirichlet and impedance boundary value problems for the Helmholtz equation in a non-locally perturbed half-plane. These boundary value problems arise in a study of time-harmonic acoustic scattering of an incident field by a sound-soft, infinite rough surface where the total field vanishes (the Dirichlet problem) or by an infinite, impedance rough surface where the total field satisfies a homogeneous impedance condition (the impedance problem). We propose a new boundary integral equation formulation for the Dirichlet problem, utilizing a combined double- and single-layer potential and a Dirichlet half-plane Green's function. For the impedance problem we propose two boundary integral equation formulations, both using a half-plane impedance Green's function, the first derived from Green's representation theorem, and the second arising from seeking the solution as a single-layer potential. We show that all the integral equations proposed are uniquely solvable in the space of bounded and continuous functions for all wavenumbers. As an important corollary we prove that, for a variety of incident fields including an incident plane wave, the impedance boundary value problem for the scattered field has a unique solution under certain constraints on the boundary impedance. Copyright © 2003 John Wiley & Sons, Ltd. [source] Experimental evaluation of the phase of the field scattered by microstrip patches for reflect-array designMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2002F. Venneri Abstract The determination of the phase of the field scattered from microstrip patches is a key factor in the design of reflect-array antennas. Although the problem has been treated in a number of theoretical articles, an experimental characterization of a such an important parameter has never been considered. In this Letter an experimental study of the phase of the field reradiated from small arrays of patches is presented. As a result a diagram of the phase of the scattered field versus the size of the patches is obtained. Results have been compared with the ones obtained with a commercial MoM package. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 163,164, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10403 [source] Scattering relations for point-source excitation in chiral mediaMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 1 2006Christodoulos Athanasiadis Abstract A spherical electromagnetic wave propagating in a chiral medium is scattered by a bounded chiral obstacle which can have any of the usual properties. Reciprocity and general scattering theorems, relating the scattered fields due to scattering of waves from a point source put in any two different locations are established. Applying the general scattering theorem for appropriate locations and polarizations of the point source we prove an associated forward scattering theorem. Mixed scattering relations, relating the scattered fields due to a plane wave and the far-field patterns due to a spherical wave, are also established. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||