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Yayın Scattering of electromagnetic waves by a rectangular impedance cylinder(Elsevier Science, 2000-04) Topsakal, Erdem; Büyükaksoy, İbrahim Alinur; İdemen, Mehmet MithatA uniformly valid asymptotic solution is developed for the diffraction of a high-frequency wave by an infinitely long rectangular cylinder having different impedance walls. The incident wave is generated by a line source located parallel to the cylinder. The problem is reduced first to a system of modified Wiener-Hopf equations involving infinitely many unknown constants and then to a couple of infinite system of linear algebraic equations which are solved numerically. Explicit expressions of the dominant wave components existing in different regions are found. Some illustrative examples show the capability of the approach.Yayın Influence of the velocity on the energy patterns of moving scatterers(Taylor & Francis, 2004) İdemen, Mehmet Mithat; Alkumru, AliParallel to the developments in the communication through space vehicles achieved during the last two decades, the scattering problems connected with moving objects became more and more important from both theoretical and practical points of view. Same problems are also arisen in point of space science, radio astronomy, radar techniques and particle physics. The earlier investigations available in the open literature concern the analysis of the scattered field pattern and, hence, treat the polarization, frequency shift (Doppler effect), aberration, etc, which are all important from both pure scientific and technological points of view. But, another issue which is also important in regard to the communication, antennas and particle physics is the influence of the motion on the scattered energy patterns which involves the radar cross-section and scattering coefficient. This paper is devoted to this purpose and aims to study the influence of the velocity on the received and scattered energies. Notice that the scattered wave is not time-harmonic even though the incident wave is so because the Lorentz transformation formulas interrelate the space coordinates and time, which makes impossible to extend the notion of radar cross-section to moving bodies. For the sake of simplicity of the mathematical manipulations, only two-dimensional case is taken into account but the method can be adapted by straightforward extensions to other types of scatterer.Yayın The confluent edge and tip singularities of the electromagnetic wave on material sheets(2004) İdemen, Mehmet MithatThe singularities of the electromagnetic wave at sharp edges and tips effect the performance of electric devices and, hence, requires serious precautions at both the design and production stages. Furthermore, in theoretical investigations they cause to some hard mathematical difficulties. Their knowledge in analytical investigations permits one to determine some auxiliary functions while in numerical works they enable one to improve the convergence of some procedures if the singularities are incorporated into the field expressions explicitly. Therefore, one has to know the types as well as the orders of possible singularities for various situations. This work is devoted to the investigation of these singularities in their most general framework.Yayın A generalization of the Wiener-Hopf approach to direct and inverse scattering problems connected with non-homogeneous half-spaces bounded by n-part boundaries(Oxford Univ Press, 2000-08) İdemen, Mehmet Mithat; Alkumru, AliThe classical Wiener-Hopf method connected with mixed two-part boundary-value problems is generalized to cover n-part boundaries. To this end one starts from an ad-hoc representation for the Green function, which involves n unknown functions having certain analytical properties. Thus the problem is reduced to a functional equation involving n unknowns, which constitutes a generalization of the classical Wiener-Hopf equation in two unknowns. To solve this latter which cannot be solved exactly when n greater than or equal to 3, one establishes a new method permitting one to obtain the asymptotic expressions valid when the wavelength is sufficiently small as compared with the widths of the inner strips of the boundary. The essentials of the method are elucidated through a concrete inverse scattering problem whose aim is to determine the constitutive electromagnetic parameters of a slab and a half-space bounded by an n-part impedance plane. Some illustrative numerical examples show the applicability as well as the accuracy of the method.
