摘要:

A solution to the problem of diffraction of an E -polarized plane wave by two adjacent imperfectly conducting dielectric quarter-spaces is given. The solution obtained is represented in an implicit form in terms of solutions to integral equations for the Fourier transforms of the surface fields. The integral equations are solved by using an iterative method. When the wavenumbers of the quarter-spaces are suitably restricted, the successive approximations of the iterative scheme converge to the unique solution of the diffraction problem. The far field is constructed from the Fourier transform of the surface field. A useful approximate expression for the far field is obtained; the accuracy depends on the wavenumbers and the refractive indices of the media in the quarter-spaces. The far field obtained from the iterative solution is compared to the far field behavior predicted by an approximate solution which is based on impedance boundary conditions.

ISSN:0920-5071    

DOI:10.1163/156939394X00100

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The static problem of two contacting conducting spheres of different radii has been studied by many authors for many years, mainly from the physical intuition of electric images. In this paper we employ the rotational degenerated coordinate system to express the field in both series and integral form, which is convenient for numerical calculation, and the picture of images follows readily.

ISSN:0920-5071    

DOI:10.1163/156939394X00119

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A two-dimensional (2-D) finite-difference time-domain (FDTD) method using a triangular grid is introduced for solving electromagnetic scattering problems. The 2-D FDTD method is based on a control region approximation, which is defined by the Dirichlet tessellation of the triangular grid. In general, this discretization scheme is accurate to second-order in time, to first-order in space for non-uniform grids, and to second-order in space for uniform grids. Using triangular grids, arbitrary geometries can be represented by piecewise linear models . In addition, an absorbing boundary condition on a smooth outer boundary, such as a circular boundary, can be implemented. This method is illustrated and verified by calculating scattering from perfectly conducting and coated objects. It is shown that geometrical modeling using a triangular grid is more accurate for electromagnetic scattering problems than those using a rectangular grid, especially when the surface wave is significant.

ISSN:0920-5071    

DOI:10.1163/156939394X00128

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper discusses the equivalent source method for scattering from three dimensional bodies of a perfect conductor. The key of this method is to approximate the scattering fields in terms of the fields generated by the hypothetical dipoles. Example scatterers discussed here are finite cylinders with rotational symmetry, and the calculated results are compared with the results obtained by other numerical methods and also with experiments that we took. Furthermore, two efficient numerical techniques incorporated with the present equivalent source method are proposed, which are useful for a scatterer with large diameter compared to the wavelength and for a slender scatterer, respectively.

ISSN:0920-5071    

DOI:10.1163/156939394X00137

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The inverse scattering problem of determining the electromagnetic characteristics, namely, conductivity, permittivity and permeability profiles of an inhomogeneous one-dimensional layered medium is presented in the time domain utilizing the layer-stripping procedure. A fully explicit numerical algorithm is proposed for simultaneous extraction of the electrical parameters by simulating a real-time wave propagation and scattering based on the Finite-Difference Time-Domain method. This yields an efficient profile inversion technique suitable for layered medium synthesis. Examples of the one-dimensional conductivity and permittivity profile inversions are also presented including the depth of the medium probed.

ISSN:0920-5071    

DOI:10.1163/156939394X00146

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper introduces a technique for time-domain electromagnetic inverse scattering based upon the use of a two-dimensional, finite-difference time-domain (FD-TD) forward scattering field representation in numerical feedback loop with a nonlinear optimization routine. Causality is exploited to reconstruct the actual target surface contour in a sequential and cumulative manner as the illuminating wavefront sweeps across the target. This approach appears to require a minimum amount of scattered field information. A number of examples are reported where the only data needed is the time waveform of a scattered pulse for the transverse magnetic (TM) polarization case, observed at just a single point in the near field. These examples include the reconstruction of two-dimensional conducting and homogeneous dielectric target shapes such as triangles, rectangles, and trapezoids. A dielectric target with reentrant features, resembling the letter "J" is also reconstructed from a single point observation. The effects of measurement signal-to-noise ratio upon this inverse-scattering technique are determined via numerical experiments. These effects are discussed in two contexts: 1) probability of exact reconstruction vs. signal-to-noise ratio, and 2) sensitivity of reconstructions to noise. It is shown that, even at low signal-to-noise ratios (where the probability of exact reconstruction is also low), the imperfectly-reconstructed targets retain many of the distinguishing features of the original target. This indicates that the reconstruction process is quite robust relative to noise. Developments in nonlinear optimization appear promising for further improving the reliability and quality of target reconstruction in noise.

ISSN:0920-5071    

DOI:10.1163/156939394X00155

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00164

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00173

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00182

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor