摘要:

A new inversion algorithm for reconstructing electrical property distributions of lossy cylindrical objects by means of time-domain data is presented. The algorithm is based on iterative solutions of an optimization process with an edge preserving regularization. The finite-difference time-domain (FDTD) method is used effectively as forward and backward solvers in each iteration. Numerical simulations are carried out to show the feasibility of detecting tumors with this reconstruction algorithm.

ISSN:0920-5071    

DOI:10.1163/156939300X00383

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

To see the similarities and differences with eletromagnetics, basic concepts and equations of elastodynamics are formulated in coordinate-free form applying concepts from Polyadic Algebra. Plane-wave propagation is studied for time-harmonic equations in isotropic and simple uniaxially anisotropic media and the Green dyadic is derived for the isotropic medium. As an extension, the Green dyadic for the anisotropic elastic medium is derived in perturbational approximation. In the Appendix A, some basic properties for tetradics, useful for practical analysis both in elastodynamics as well as in electromagnetics, are derived.

ISSN:0920-5071    

DOI:10.1163/156939300X00392

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, the scanning characteristics of an infinite stacked microstrip phased array in a three-layered structure are analysed. In the analysis of the field distribution, the spectral-domain Galerkin Method of Moments together with the planar dyadic Green's function is applied. An attachment mode current is employed to model the singularity of currents nearby the feed point so as to facilitate the fast convergence. The currents on all patches are expanded in terms of the trigonometric basis and weighting functions in the entire domain. The normalized patterns of the infinite microstrip array are computed in this paper and the scanning features of the antenna against the scanning angle and frequency are discussed in both the E- and H-planes.

ISSN:0920-5071    

DOI:10.1163/156939300X00400

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper presents an alternative vector analysis of the electromagnetic (EM) fields radiated from electrically small thin square and rectangular loop antennas of arbitrary length 2a and width 2b . This method employs the dyadic Green's function (DGF) in the derivation of the EM radiated fields and thus makes the analysis general, compact and straightforward. Both near- and far-zones are considered so that the EM radiated fields are expressed in terms of the vector wave eigenfunctions. Not only the exact solution of the EM fields in the near and far zones outside the region (where r > √a2 + b2 ) is derived by use of spherical Hankel functions of the first kind, but also the closed series form of the EM fields radiated in the near zone inside the region 0 r < b is obtained in series of spherical Bessel functions of the first kind. The two regions between the radial distances b and √a2 + b2 which are defined as intermediate zones are characterized by both the spherical Bessel and Hankel functions of the first kind. Validity of the numerical results is discussed and clarified.

ISSN:0920-5071    

DOI:10.1163/156939300X00419

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper considers expressions of the dyadic Green's function for rectangular enclosures, which are efficient from a computational point of view. The inherent application is to solve numerically electromagnetic scattering problems with an integral equation formulation, using the Method of Moments. The Green's dyadic is derived from an image-spectral approach, which has the flexibility to generate directly the expression with the fastest convergence once the locations of both the observation and the source points are given. When the observation point is at the source region, slowly converging sums arise that are overcome by extending the method of Ewald to the dyadic case. Numerical proofs are reported in tabular form to validate the technique developed.

ISSN:0920-5071    

DOI:10.1163/156939300X00428

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Reconstructions of two dimensional dielectric or conducting objects from multi-frequency experimental data are considered in the present paper. Two different iterative methods are used for solving the inverse scattering problem. The first one is based on a boundary integral formalism and retrieves boundaries and complex permittivities of unknown homogeneous scatterers. For this method initial guesses are derived from method of decomposition of the time reversal operator (DORT) combined with a low frequency approximation. The second method is based on a domain integral formalism and retrieves the relative complex permittivity distribution inside some investigated domain. The data were carried out in a controlled environment (anechoic chamber) and the reconstructions have been performed using multifrequency approach, i.e., the scheme starts with the lowest available frequency and uses the final result as initial guess at higher frequency in order to enhance the resolution.

ISSN:0920-5071    

DOI:10.1163/156939300X00437

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, we introduce a modified FDTD model in order to investigate the behavior of the induced voltage of a non-uniform transmission line (TL) excited by lumped voltage sources or external electromagnetic wave. The parameters to be taken into account for this specific coupling phenomenon are explicitly analyzed and the affection on the behavior of the induced voltage is discussed in detail. To confirm the validity of this model, results obtained by this model, for two typical transmission line configurations, are compared to results obtained by other models, already published in the literature. Finally, several numerical calculations of the line responses are provided for non-uniform TL's that can be present in practical configurations. These results indicate that a configuration slightly different from the uniform one can cause large discrepancies on the termination voltages of the TL.

ISSN:0920-5071    

DOI:10.1163/156939300X00446

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, we introduce a new classification scheme for dual frequency polarimetric SAR data sets. A (6 x 6) polarimetric coherency matrix is defined to simultaneously take into account the full polarimetric information from both images. This matrix is composed of the two coherency matrices and their cross-correlation. A decomposition theorem is applied to both images to obtain 64 initial clusters based on their scattering characteristics. The data sets are then classified by an iterative algorithm based on a complex Wishart density function of the 6 by 6 matrix. A class number reduction technique is then applied on the 64 resulting clusters to improve the efficiency of the interpretation and representation of each class characteristics. An alternative technique is also proposed which introduces the polarimetric cross-correlation information to refine the results of classification to a small number of clusters using the conditional probability of the cross-correlation matrix. The analysis of the resulting clusters is realized by determining the rigorous change in polarimetric properties from one image to the other. The polarimetric variations are parameterized by 8 real coefficients derived from the decomposition of a special unitary operator on the Gell-Mann basis. These classification and analysis schemes are applied to full polarimetric P, L, and C bands SAR

ISSN:0920-5071    

DOI:10.1163/156939300X00455

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We present a different approach of dealing with integral equations developed to tackle diffraction of scalar harmonic waves by a hole in a perfectly reflecting screen with a thickness assumed to be negligibly small. This approach uses a cartesian representation of the Green's functions which satisfy on the screen the same Dirichlet or Neumann boundary conditions as the total field incident, reflected and diffracted while the continuity of the total field is imposed through the aperture. The solution of the corresponding integral equations is given harmonic plane waves with an application to the diffraction at slits and rectangular apertures.

ISSN:0920-5071    

DOI:10.1163/156939300X00464

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An approach based on integral equations, different from the conventional ones, was previously applied [1] to the diffraction of scalar waves at plane apertures. The same technique generalized to vector integral equations with tensor Green's functions solutions of Maxwell's equations, is used to deal with the diffraction of electromagnetic plane waves. Explicit formulae are given for the electric field with an application to the diffraction by a slit.

ISSN:0920-5071    

DOI:10.1163/156939300X00473

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor