Necmi Serkan Tezel

A second order Newton method for sound soft inverse obstacle scattering

Abstract A new second order Newton method for reconstructing the shape of a sound soft scatterer from the measured far-field pattern for scattering of time harmonic plane waves is presented. This method extends a hybrid between regularized Newton iterations and decomposition methods that has been suggested and analyzed in a number of papers by Kress and Serranho [Inverse Problems 19: 91–104, 2003, Inverse Problems 21: 773–784, 2005, J. Comput. Appl. Math. 204: 418–427, 2007, Inverse Problems 22: 663–680, 2006, Inverse Problems and Imaging 1: 691–712, 2007] and has some features in common with the second degree method for ill-posed nonlinear problems as considered by Hettlich and Rundell [SIAM J.Numer. Anal. 37: 587–620, 2000]. The main idea of our iterative method is to use Huygens principle, i.e., represent the scattered field as a single-layer potential. Given an approximation for the boundary of the scatterer, this leads to an ill-posed integral equation of the first kind that is solved via Tikhonov regularization. Then, in a second order Taylor expansion, the sound soft boundary condition is employed to update the boundary approximation. In an iterative procedure, these two steps are alternated until some stopping criterium is satisfied. We describe the method in detail and illustrate its feasibility through examples with exact and noisy data.

Bi-static scattering width control of multiple coated PEC cylinder

In this study, we propose the method that determines the coated parameter values of the cylinder satisfying the desired bistatic scattering width (SW). We consider the infinitely long perfectly electric conductor (PEC) cylinder, which is illuminated by plane wave whose polarization is parallel to cylinder axis. Unknown scattered field coefficients are expressed by using boundary conditions in terms of coating parameters for fixed wavelength and radius of cylinder. Far field SW is obtained using the scattered coefficients and then steepest descent method is used to control the bi-static SW according to each coating complex wave number and thickness. Minimised bi-static SW was compared to those of PEC cylinder and good reduction values were observed over a wide frequency range and angle.

Evaluation of the scattering matrix for impedance sphere

In this work, scattering matrix of the constant impedance sphere is investigated by using series expansion of the incident and the scattering field. Using impedance boundary condition, unknown coefficients in the scattering field were found. We consider the there dimensional case as, sphere is illuminated by plane wave that be along z direction. We obtained the general expressions of the scattered field. Then we sought for the scattering matrix for the y-z plane

Coupling effects of the impedance cylinder located between the parallel lines

In this work, coupling effect of the arbitrary impedance cylinder with any arbitrary cross section located between the parallel lines is investigated by using the method of moment techniques. We consider the two dimensional case as, lines and cyfinder are infinite along the z axis. The effects of the induced currents on the impedance cylinder were expressed due to the current of line by numerically. The coupling degree of cylinder properties was investigated. As an example, coupling effect of the constant impedance circular cylinder is given for different impedance cylinder parameters. Kevwords: Coupling effect, Impedance cylinder, Parallel lines Introduction Due to the appearance of non-uniform electrical structures in our environment, the scattering of electromagnetic waves by cylindrical bodies becomes an important issue in microwave communication systems and circuits. Although the topic i s obviously important, it has not yet been thoroughly discussed in the literature because ir yields exaemely diffcult mathematical problems. Mei and Van Blade1 [ I J who formulated the problem in terms of an integral equation and then solved it numerically. Later, Bumside et al.(ZJ treated the same problem by using the geometrical theory of diffraction combined with the moment method. I t is worth nothing here the cases considered in these works are related to perfectly conducting bodies. Same problem was investigated by Erdem Topsakal and Alinur Buyukaksoy[3] using Wiener Hopf equation for rectangular cylinder containing that each wall has different impedance value, but this solution is only valid for rectangular cylinder and can not be applied any cross section and arbitrary impedance change. The aim of the this study is to consider this problem with method of moment. In our problem, we will use expuwt) for the time dependence of wave. The geometry of the problem is shown in Fig. I . An infinitely long arbitrary cross section cylinder is illuminated by an infinitely long line source located parallel to the cylinder. The face of the cylinder are characterized by surface impedance changing by angular position and its cross section by Z(

Newton's method for inverse obstacle scattering of buried objects

) and r(

Bi-static radar cross section (RCS) reduction of impedance cylinder

) respectively In next section, the problem is first formulated as a boundary value problem. By using the moment method, unknown magnetic and electric currents which satisfy impedance boundary condition on the surface of the cylinder is determined. Formulation of the problem In the case that the relative permittivity or permeability of a scatterer is large or perfect electric conductor coated by isolator such as paint, an approximate impedance boundary condition (IBC) can be used to simplify the problem formulation. 0-7803-7779-6/03/

Interference reduction by adaptive weighting using steepest descent method for any array configuration

17.0

A new formulation and solution method of electromagnetic scattering from arbitrary shaped dielectric objects

A Newton method to reconstruct the shape of a buried sound soft object through the measured far-field scattering data is given. The scattered field is represented as a singlelayer potential which leads to an ill-posed integral equation of the first kind that is solved via Tikhonov regularization. The presented Newton based method combines ideas of both the iterative and decomposition methods and inherits the advantages of each of them, such as getting good reconstructions and not requiring a forward solver at each step. The numerical results show that the method yields good reconstruction.

Electromagnetic scattering from cylinder described by high‐order inhomogeneous impedance boundary conditions

Reduction of RCS of military targets is important issue and can be regarded as part of passive ECM (electronic counter measure). Reduction of RCS is basically made by multilayer coating the surface of the target by lossy dielectrics. In this case, boundary condition which is satisfied on the surface of target can be modelled by IBC (impedance boundary condition). We propose the method that determines the surface impedance value of the cylinder satisfying reduced bi-static RCS. We also applied the proposed method to minimize the mono-static RCS of the impedance cylinder. Minimized mono-static RCS was compared to those of perfectly electrical conductor (PEC) cylinder and good reduction values were observed over a wide frequency range and angle.

Inserting Moving Targets to Polarimetric SAR Image by Self Deception Jamming

In this study, maximisation of gain of the antenna array into target direction to those of interference direction is addressed by adaptive weighting of received signals for any array configuration. These coefficients set is found by steepest descent method. As an example, this algorithm is applied for planar array and good reduction values are observed