Home About us Contact
|
Home About us Contact | ||
|
|
||
Scattering Object (scattering + object)
Selected AbstractsThe performance of spheroidal infinite elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001R. J. Astley Abstract A number of spheroidal and ellipsoidal infinite elements have been proposed for the solution of unbounded wave problems in the frequency domain, i.e solutions of the Helmholtz equation. These elements are widely believed to be more effective than conventional spherical infinite elements in cases where the radiating or scattering object is slender or flat and can therefore be closely enclosed by a spheroidal or an ellipsoidal surface. The validity of this statement is investigated in the current article. The radial order which is required for an accurate solution is shown to depend strongly not only upon the type of element that is used, but also on the aspect ratio of the bounding spheroid and the non-dimensional wave number. The nature of this dependence can partially be explained by comparing the non-oscillatory component of simple source solutions to the terms available in the trial solution of spheroidal elements. Numerical studies are also presented to demonstrate the rates at which convergence can be achieved, in practice, by unconjugated-(,Burnett') and conjugated (,Astley-Leis')-type elements. It will be shown that neither formulation is entirely satisfactory at high frequencies and high aspect ratios. Copyright © 2001 John Wiley & Sons, Ltd. [source] Superresolution planar diffraction tomography through evanescent fields,INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 1 2002Sean K. Lehman We consider the problem of noninvasively locating objects buried in a layered medium such as land mines in the ground or objects concealed in a wall. In such environments, the transmitter(s) and receiver(s) are frequently within the near-field region of the illuminating radiation. In these cases, the scattered evanescent field carries useful information on the scattering object. Conventional diffraction tomography techniques neglect, by their design, the evanescent field. Under near-field conditions, they treat it as noise as opposed to valid data. If correctly incorporated into a reconstruction algorithm, the evanescent field, which carries high spatial frequency information, can be used to achieve resolution beyond the classical limit of ,/2, or "superresolution." We build on the generalized holography theory presented by Langenberg to develop a planar diffraction tomography algorithm that incorporates evanescent field information to achieve superresolution. Our theory is based on a generalization of the Fourier transform, which allows for complex spatial frequencies in a manner similar to the Laplace transform. We specialize our model to the case of a two-dimensional multimonostatic, wideband imaging system, and derive an extended resolution reconstruction procedure. We implement and apply our reconstruction to two data sets collected using the Lawrence Livermore National Laboratory (LLNL) Micropower Impulse Radar (MIR). © 2002 John Wiley & Sons, Inc. Int J Imaging Syst Technol 12, 16,26, 2002 [source] Use of wavelet transform to the method-of-moments matrix arising from electromagnetic scattering problems of 2D objects due to oblique plane-wave incidenceMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2002Jin Yu Abstract An efficient method is presented for transforming the matrix of the method of moments obtained by the expansion of the unknown surface currents with pulse basis function and the use of point match testing to a matrix with wavelet basis and testing functions. When the electromagnetic scattering object is a dielectric or object under oblique plane-wave incidence, more than one equivalent surface current component exists at the object surface. When these currents are connected into one current vector in the method of moments, there must be some discontinuities between the current components. These discontinuities make the direct wavelet transform to the whole MoM matrix inefficient and not equivalent to the use of the wavelet functions in the expansion of the unknown currents and the testing. Therefore, the wavelet transform must be constructed in a different way to avoid these discontinuities. Here, the proper wavelet transform that is equivalent to the use of the wavelet functions in the MoM, which avoids such discontinuities, is presented. This transform is referred to as wavelet subtransform. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 130,134, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10394 [source] Investigating the performance of MIMO systems from an electromagnetic perspectiveMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2006Marek E. Bialkowski Abstract Multiple input multiple output (MIMO) wireless systems use multiple element antennas (MEAs) at the transmitter (TX) and the receiver (RX) in order to offer improved information rates (capacity) over conventional single antenna systems in rich scattering environments. In this paper, an example of a simple MIMO system is considered in which both antennas and scattering objects are formed by wire dipoles. Such a system can be analyzed in the strict electromagnetic (EM) sense and its capacity can be determined for varying array size, interelement spacing, and distributions of scatterers. The EM model of this MIMO system can be used to assess the validity of single- or double-bounce scattering models for mixed line of sight (LOS) and non-line of sight (NLOS) signal-propagation conditions. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1233,1238, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21664 [source] Extension of impedance matrix compression method with wavelet transform for 2-D conducting and dielectric scattering objects due to oblique plane-wave incidenceMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2002Jin Yu Abstract The impedance matrix compression (IMC) technique is applied to analyze the square method,of-moments (MoM) matrix arising from the surface integral equation for 2-D conducting and dielectric objects with oblique plane-wave incidence. The induced current components are processed separately by using wavelet basis functions. The comparison between cylinders with circular and square cross section is presented to show the effectiveness of IMC, which depends on the geometry of the object and the wavelet transform matrix. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 53,56, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10371 [source] | ||||||||||