The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Prabhakar H. Pathak - One of the best experts on this subject based on the ideXlab platform.
-
A Uniform Geometrical Theory of Diffraction for Vertices Formed by Truncated Curved Wedges
IEEE Transactions on Antennas and Propagation, 2015Co-Authors: Matteo Albani, Giorgio Carluccio, Prabhakar H. PathakAbstract:A uniform geometrical theory of diffraction (UTD) Ray analysis is developed for analyzing the problem of electromagnetic (EM) scattering by vertices at the tip of a pyramid formed by curved surfaces with curvilinear edges when illuminated by an arbitrarily polarized astigmatic wavefront. The UTD vertex diffraction coefficient involves various geometrical parameters such as the local radii of curvature of the faces of the pyramid, of its edges, and of the Incident Ray wavefront, and it is able to compensate for those discontinuities of the field predicted by the UTD for edges (i.e., geometrical optics (GO) combined with the UTD edge diffracted Rays) occurring when an edge diffraction point lies at the tip or vertex. This provides an effective engineering tool able to describe the field scattered by truncated edges in curved surfaces within a UTD framework, as required in modern Ray-based codes. Some numerical examples highlight the accuracy and the effectiveness of the proposed UTD Ray solution for vertex diffraction.
-
Uniform Ray Description for the PO Scattering by Vertices in Curved Surface With Curvilinear Edges and Relatively General Boundary Conditions
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: Matteo Albani, Giorgio Carluccio, Prabhakar H. PathakAbstract:A new high-frequency analysis is presented for the scattering by vertices in a curved surface with curvilinear edges and relatively general boundary conditions, under the physical optics (PO) approximation. Both, impenetrable (e.g., impedance surface, coated conductor) as well as transparent thin sheet materials (e.g., thin dielectric, or frequency selective surface) are treated, via their Fresnel reflection and transmission coefficients. The PO scattered field is cast in a uniform theory of diffraction (UTD) Ray format and comprises geometrical optics, edge and vertex diffracted Rays. The contribution of this paper is twofold. First, we derive PO-based edge and vertex diffraction coefficients for sufficiently thin but relatively arbitrary materials, while in the literature most of the results (especially for vertex diffraction) are valid only for perfectly conducting objects. Second, the shadow boundary transitional behavior of edge and vertex diffracted fields is rigorously derived for the curved geometry case, as a function of various geometrical parameters such as the local radii of curvature of the surface, of its edges and of the Incident Ray wavefront. For edge diffracted Rays, such a transitional behavior is found to be the same as that obtained heuristically in the original UTD. For vertex diffracted Rays, the PO-based transitional behavior is a novel result providing offers clues to generalize a recent UTD solution for a planar vertex to treat the present curved vertex problem. Some numerical examples highlight the accuracy and the effectiveness of the proposed Ray description.
-
A UTD for the Radiation by Sources near Thin Planar Metamaterial Structures with a Discontinuity
2007 Asia-Pacific Microwave Conference, 2007Co-Authors: Titipong Lertwiriyaprapa, Prabhakar H. Pathak, John L. VolakisAbstract:The development of asymptotic high-frequency, uniform geometrical theory of diffraction (UTD) solutions, which will identify and quantify all the pertinent Ray mechanisms for predicting, in a relatively simple closed form, the high frequency radiation characteristics of practical, planar, metamaterial (MTM) antenna structures is presented in this paper. In particular, the present analytical UTD development can, in a physically appealing manner, characterize the diffraction of Incident Ray fields, and especially the launching and diffraction of backward surface waves (BSWs), respectively, from the ends (or the truncation) of finite size MTM slabs, with or without a perfect electric conductor (PEC) or ground plane backing. The ansatz for the proposed solution is based on the Wiener-Hopf (W-H) solution to a problem of the plane wave diffraction by a two part impedance surface. The present solutions are simpler to use because they do not contain the complicated split functions of the W-H solutions nor the complex Maliuzhinets functions. The present solutions recover the proper local plane wave Fresnel reflection and transmission coefficients and surface wave constants for the MTM. Besides being asymptotic solutions of the wave equation, the present UTD solutions, which are developed via a partially heuristic spectral synthesis approach, satisfy reciprocity, PEC boundary conditions, and the Karp-Karal lemma which dictates that the first order UTD space waves vanish on the material interface.
Matteo Albani - One of the best experts on this subject based on the ideXlab platform.
-
A Uniform Geometrical Theory of Diffraction for Vertices Formed by Truncated Curved Wedges
IEEE Transactions on Antennas and Propagation, 2015Co-Authors: Matteo Albani, Giorgio Carluccio, Prabhakar H. PathakAbstract:A uniform geometrical theory of diffraction (UTD) Ray analysis is developed for analyzing the problem of electromagnetic (EM) scattering by vertices at the tip of a pyramid formed by curved surfaces with curvilinear edges when illuminated by an arbitrarily polarized astigmatic wavefront. The UTD vertex diffraction coefficient involves various geometrical parameters such as the local radii of curvature of the faces of the pyramid, of its edges, and of the Incident Ray wavefront, and it is able to compensate for those discontinuities of the field predicted by the UTD for edges (i.e., geometrical optics (GO) combined with the UTD edge diffracted Rays) occurring when an edge diffraction point lies at the tip or vertex. This provides an effective engineering tool able to describe the field scattered by truncated edges in curved surfaces within a UTD framework, as required in modern Ray-based codes. Some numerical examples highlight the accuracy and the effectiveness of the proposed UTD Ray solution for vertex diffraction.
-
Uniform Ray Description for the PO Scattering by Vertices in Curved Surface With Curvilinear Edges and Relatively General Boundary Conditions
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: Matteo Albani, Giorgio Carluccio, Prabhakar H. PathakAbstract:A new high-frequency analysis is presented for the scattering by vertices in a curved surface with curvilinear edges and relatively general boundary conditions, under the physical optics (PO) approximation. Both, impenetrable (e.g., impedance surface, coated conductor) as well as transparent thin sheet materials (e.g., thin dielectric, or frequency selective surface) are treated, via their Fresnel reflection and transmission coefficients. The PO scattered field is cast in a uniform theory of diffraction (UTD) Ray format and comprises geometrical optics, edge and vertex diffracted Rays. The contribution of this paper is twofold. First, we derive PO-based edge and vertex diffraction coefficients for sufficiently thin but relatively arbitrary materials, while in the literature most of the results (especially for vertex diffraction) are valid only for perfectly conducting objects. Second, the shadow boundary transitional behavior of edge and vertex diffracted fields is rigorously derived for the curved geometry case, as a function of various geometrical parameters such as the local radii of curvature of the surface, of its edges and of the Incident Ray wavefront. For edge diffracted Rays, such a transitional behavior is found to be the same as that obtained heuristically in the original UTD. For vertex diffracted Rays, the PO-based transitional behavior is a novel result providing offers clues to generalize a recent UTD solution for a planar vertex to treat the present curved vertex problem. Some numerical examples highlight the accuracy and the effectiveness of the proposed Ray description.
Thomas Kaiser - One of the best experts on this subject based on the ideXlab platform.
-
A Comparison Study of Non-specular Diffuse Scattering Models at Terahertz Frequencies
2018 First International Workshop on Mobile Terahertz Systems (IWMTS), 2018Co-Authors: Fawad Sheikh, Dien Lessy, Mai Alissa, Thomas KaiserAbstract:At terahertz (THz) frequencies, dimensions of optically thin building materials (e.g., sand-lime brick, gypsum plaster) are comparable to or even larger than the wavelength. Such materials, normally neglected and assumed smooth evidently become rough now. A smooth material will reflect the Incident Ray specularly in a single direction, whilst a rough material will scatter it into various directions. Perhaps, for very rough materials the specular reflection loses its privileged position, and the non-specular diffusely scattered Rays dominate the reflection behaviour. Likewise, a widely known fact that the surface roughness alters the scattered field far more than its electrical properties, emphasizes that these unique features lead to new multipath scattering models to characterize the THz channel. Effective Roughness (ER) and Beckmann-Kirchhoff (B-K) models address the problem of diffuse scattering by means of approximate models. This paper compares the aforementioned models considering the impact of diffuse scattering on total received power by employing Ray-tracing tool in an indoor office environment. For this study, particular attention is diverted to the non-line-of-sight (NLoS) scenario due to its imminence in terms of coverage and performance.
-
A Novel Ray-Tracing Algorithm for Non-Specular Diffuse Scattered Rays at Terahertz Frequencies
2018 First International Workshop on Mobile Terahertz Systems (IWMTS), 2018Co-Authors: Fawad Sheikh, Dien Lessy, Thomas KaiserAbstract:This paper presents a novel self-programmed three-dimensional (3D) Ray-tracing algorithm (RTA) based on Beckmann-Kirchhoff (B-K) model for modeling diffuse scattering mechanism in non-specular directions at terahertz (THz) frequencies. The terahertz or submillimeter-wave frequencies pose unique challenges for channel modeling due to sparse and extreme frequency selective behaviour of the propagation mechanism. In particular, the most critical feature proved to provide important contributions in determining spatial and temporal dispersion in the submillimeter-wave band is the diffuse scattering mechanism, wherein an Incident Ray may split into a specular and several non-specular (diffused scattered) Rays after bouncing off from rough materials. This makes the diffuse scattering or scattering from rough surfaces a necessary design consideration constituting a high proportion of all the propagation Rays and hence, must be accounted for propagation modeling to accurately predict channel characteristics. Next, we integrate our MATLAB-based proposed algorithm to a commercial Ray-tracing tool to derive a spatiotemporal model of scattered multipath propagation channels considering rough materials in a realistic office environment for both line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios. So far none of the commercially available Ray-tracing tools have implemented this scattering model yet.
Giorgio Carluccio - One of the best experts on this subject based on the ideXlab platform.
-
A Uniform Geometrical Theory of Diffraction for Vertices Formed by Truncated Curved Wedges
IEEE Transactions on Antennas and Propagation, 2015Co-Authors: Matteo Albani, Giorgio Carluccio, Prabhakar H. PathakAbstract:A uniform geometrical theory of diffraction (UTD) Ray analysis is developed for analyzing the problem of electromagnetic (EM) scattering by vertices at the tip of a pyramid formed by curved surfaces with curvilinear edges when illuminated by an arbitrarily polarized astigmatic wavefront. The UTD vertex diffraction coefficient involves various geometrical parameters such as the local radii of curvature of the faces of the pyramid, of its edges, and of the Incident Ray wavefront, and it is able to compensate for those discontinuities of the field predicted by the UTD for edges (i.e., geometrical optics (GO) combined with the UTD edge diffracted Rays) occurring when an edge diffraction point lies at the tip or vertex. This provides an effective engineering tool able to describe the field scattered by truncated edges in curved surfaces within a UTD framework, as required in modern Ray-based codes. Some numerical examples highlight the accuracy and the effectiveness of the proposed UTD Ray solution for vertex diffraction.
-
Uniform Ray Description for the PO Scattering by Vertices in Curved Surface With Curvilinear Edges and Relatively General Boundary Conditions
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: Matteo Albani, Giorgio Carluccio, Prabhakar H. PathakAbstract:A new high-frequency analysis is presented for the scattering by vertices in a curved surface with curvilinear edges and relatively general boundary conditions, under the physical optics (PO) approximation. Both, impenetrable (e.g., impedance surface, coated conductor) as well as transparent thin sheet materials (e.g., thin dielectric, or frequency selective surface) are treated, via their Fresnel reflection and transmission coefficients. The PO scattered field is cast in a uniform theory of diffraction (UTD) Ray format and comprises geometrical optics, edge and vertex diffracted Rays. The contribution of this paper is twofold. First, we derive PO-based edge and vertex diffraction coefficients for sufficiently thin but relatively arbitrary materials, while in the literature most of the results (especially for vertex diffraction) are valid only for perfectly conducting objects. Second, the shadow boundary transitional behavior of edge and vertex diffracted fields is rigorously derived for the curved geometry case, as a function of various geometrical parameters such as the local radii of curvature of the surface, of its edges and of the Incident Ray wavefront. For edge diffracted Rays, such a transitional behavior is found to be the same as that obtained heuristically in the original UTD. For vertex diffracted Rays, the PO-based transitional behavior is a novel result providing offers clues to generalize a recent UTD solution for a planar vertex to treat the present curved vertex problem. Some numerical examples highlight the accuracy and the effectiveness of the proposed Ray description.
Cheng-lung Chiang - One of the best experts on this subject based on the ideXlab platform.
-
Enhanced polarization conversion for an anisotropic thin film
Optics Communications, 2006Co-Authors: Cheng-lung ChiangAbstract:This work presents an explicit expression for the reflection and transmission coefficients of an anisotropic thin film in the general case in which the optical axis and the Incident Ray are arbitrarily directed in three dimensions. The polarization conversion quantities for reflected light from an anisotropic thin film are calculated and analyzed for two three-layered systems. With light Incident from a dense medium, polarization conversion will be enhanced at a particular Incident angle that exceeds the critical angle.
-
Optical thickness and anisotropic orientation of a birefringent thin film: analysis from explicit expressions for reflection and transmission coefficients
Optical Engineering, 2006Co-Authors: Cheng-lung ChiangAbstract:We present explicit expressions for the reflection and transmission coefficients of an anisotropic thin film. In the general case, the optical axis and the Incident Ray are in arbitrary directions. Multireflected ordinary Rays and extraordinary Rays in the thin film are coupled to each other at the interface. The degrees of polarization conversion for reflected and transmitted light from the anisotropic thin film are calculated. The transmittance and reflectance are measured by rotating the polarization of the normal Incident Ray, and the columnar growth plane and film thickness are thus determined.
