摘要:

Moving sources and spatiotemporally dependent boundaries have been introduced in the past, in order to facilitate analyses of the so called "Doppler effect" phenomena. Here a model is introduced for generalized situations involving translatory and moving surfaces on which certain boundary or source conditions are prescribed. The ambiguity arising from analyses of Doppler-like effects in electromagnetics as well as acoustics, in which the (mathematical) translatory surface is not explicitly distinguished from the (physical) moving object is carefully discussed here, and the role of physics, e.g., in the form of Einstein's Special Relativity theory, is considered. The present approach facilitates the general reformulation of the Doppler effect class of problems and suggests meaningful first order v/c (relative velocity) approximations which can then be employed for more complicated problems. Quasi Doppler effects are introduced in order to replace the inherent "inverse problem" nature of the scattering Doppler effect with a "forward problem" formulation which allows for a broader scope of problems and approximations. This facilitates the representation of relativistically exact but complicated solutions in terms of simpler expressions involving first order velocity effects. In turn, this facilitates new approximate solutions for problems not considered previously. By further distinguishing amplitude and phase effects, even simpler expressions, inconsistent in v/c , can be used. This is also helpful in assessing the validity of some heuristic approximations suggested in the past. We start with a general analysis of the Doppler effects initiated by complicated surfaces, providing some general guidelines and insight for our ability to analyze increasingly complicated problems.

ISSN:0920-5071    

DOI:10.1163/156939399X00790

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The aim of this paper is to deal with the problem of numerical solution of two-dimensional Fredholm integral equation of the first kind. First, two-dimensional multiscale basis is introduced following the tensor product of the one-dimensional multiscale triangular basis. We also discuss the geometrical meaning of the coefficients of the multiscale basis and on the compression technique for representing the original two dimensional function of the multiscale basis. Second, by use of this kind of basis, the multiscale moment method for solving two-dimensional Fredholm integral equation of the first kind has been proposed. Furthermore, the adaptive algorithm of the multiscale moment method (AMMM) has been presented according to the characteristics of solution coefficients of the integral equation. From (V -1) -th scale to V-th scale, the approximate solution on the finer grid is predicted from the known solution on the coarse grid by use of a tensor B-spline interpolant product. Many of the numerical simulations are carried out to test the feasibility of the multiscale moment method and on how to implement the adaptive algorithm. It will be found that the adaptive algorithm can reduce the size of linear equations constructed from multiscale moment method for two-dimensional Fredholm inte

ISSN:0920-5071    

DOI:10.1163/156939399X00808

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The Kirchhoff-Huyghens diffraction integral is generalized to arbitrary time-dependent fields and used to analyse the diffraction of focus wave modes by circular and rectangular plane apertures. It is shown that their diffraction by a slit is still an open problem. The physical implications of these results are discussed.

ISSN:0920-5071    

DOI:10.1163/156939399X00817

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The problem of electromagnetic mutual coupling of scatterers in the three-dimensional regular infinite arrays is considered. The arrays are infinite in the XY-coordinate plane and finite along the OZ-axis, their volume cells have rectangular shape. Each scatterer can be described by two coupled dipoles (electric and magnetic) having the same direction, i.e., the scatterers are uniaxial chiral particles. The field interaction of these objects can be an important factor in the theory of bianisotropic composite media and also concerns the antenna array theory. A simple and rigorous model of such an interaction is developed.

ISSN:0920-5071    

DOI:10.1163/156939399X00826

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A new approach, the multipole theory (MT) method, is presented for calculating two-dimensional (2-D) Helmholtz equation problems. By the mathematical deduction, the general MT formula and its applied laws are derived. The new approach has been applied to compute the cutoff wavenumbers of a rectangular waveguide, as analytical results are available for this problem. In order to further verify the accuracy of this method, the MT method has also been applied to compute the TE and TM modes of two high power waveguides and a square offset line. Comparison of accuracy is made whenever data is available. It has been proven that the MT method is an effective approach for calculating 2-D Helmholtz equation problems.

ISSN:0920-5071    

DOI:10.1163/156939399X00835

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this contribution the technique of dyadic Green's function in terms of the normalized spherical vector wave functions is adopted for investigating the radiation of a thin circular loop antenna in a radially multilayered biisotropic sphere, and the current on the loop antenna is supposed to be a uniform, a sinusoidal as well as a generalized Fourier series distribution, respectively. The radiated fields in both near and far field zones for circular loop antenna of arbitrary radius are derived and expressed as a superposition of the right- and left-handed circularly polarized waves. Numerical results are presented to demonstrate the constitutive parameter effects of the two- and four-layer biisotropic spheres on the resonant characteristics of near fields as well as the radiated power and polarized state of the far fields for electrically large and small thin circular loop antennas excited by a uniform current, respectively.

ISSN:0920-5071    

DOI:10.1163/156939399X00844

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A multi-domain GDQ approach is presented in this paper for the analysis of various hollow conducting waveguides with rectangular boundaries. The present approach first decomposes the whole computational domain into several subdomains. Then in each sub-domain, the GDQ method is applied to discretize the derivatives in the Helmholtz equation. The resultant eigenvalue equation system is solved by the standard eigenvalue solver. It is demonstrated in this work that accurate cutoff wavenumbers can be simultaneously computed by multi-domain GDQ approach using just a few grid points. As a consequence, the required computational effort is tiny. The multi-domain GDQ results agree very well with available data in the literature. No spurious modes are found in present study.

ISSN:0920-5071    

DOI:10.1163/156939399X00853

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A graphical method for the computation of near-field scattering by electrically large scatterers is presented. A perspective transform is introduced for viewing point located in the near region of the scatterers so that the near-field effect is graphically represented. For efficient computation, a graphical algorithm of surface integration is implemented based on currently available graphics software. The concept of Generalized Radar Cross-Section (GRCS) is defined and theoretical results of GRCS of two typical scatterers are carried out.

ISSN:0920-5071    

DOI:10.1163/156939399X00862

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this work obstacle models for wave propagation over irregular terrain are investigated. Obstacles can be modeled both as perfectly conducting wedges or ellipses and impedance wedges and ellipses depending on the terrain structure and electrical properties. The irregularities of the terrain can be taken into account by surface roughness attenuation factor. The effects of different obstacle models, topographical and electrical properties of the terrain are calculated using Uniform Geometrical Theory of Diffraction for perfectly conducting and impedance surfaces. Results are compared to each other. It is shown that there is a significant difference between impedance wedge-wedge and impedance ellipse-ellipse models for low target altitudes. To calculate propagation factor precisely ellipse-ellipse model must be used for some types of terrain geometries.

ISSN:0920-5071    

DOI:10.1163/156939399X00871

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The generalized exponential matrix technique in the spectral domain is used in conjunction with Galerkin's approach to examine the dispersion characteristics of bilateral coplanar waveguide and periodic microstrip line in bianisotropic superstrate-substrate structures possessing different constitutive features, and the mathematical treatment in this study accounts for very generalized bianisotropic linear media characterized by four independent 3 x 3 constitutive tensors but within the confines of a realizable physical range. Numerical results are presented to demonstrate the combined effects of magnetoelectric cross coupling on the propagation constant of dominant mode, and some unique dispersion phenomena are illustrated and discussed.

ISSN:0920-5071    

DOI:10.1163/156939399X00880

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor