摘要:

In this paper we will study the Green dyadics and the factorization of the Helmholtz determinant operator for a new class of homogeneous bianisotropic media. That new class of media is derived from previously studied media using a rotational duality transformation. The new class of media is very general and contains many other, previously studied classes, as special cases. The Green dyadics are expressed in a form that contains a one-dimensional inverse Fourier transformation that, in general, cannot be evaluated in closed form.

ISSN:0920-5071    

DOI:10.1163/156939300X01472

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A rigorous differential method is presented for the efficient calculation of the modal scattering matrix of H-plane junctions in rectangular waveguides (filters, tapers, adapted sectoral horns). For this purpose, Maxwell's equations are used in tensorial form, written in a nonorthogonal coordinate system fitted to the studied structure geometry. The formalism requires numerical integrations with a Runge Kutta algorithm for solving an initial value problem. In order to avoid numerical instabilities we consider the transition as several elementary sections in series. When it is done, one may cascade using a generalized scattering matrix approach. This method can be used for steep discontinuities. The theory is verified by comparison with results obtained by other methods and a numerical study is proposed.

ISSN:0920-5071    

DOI:10.1163/156939300X01481

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A detailed analysis of the finite-volume, time-domain scheme, as applied to Maxwell's equations is provided herein. To accomplish the temporal discretization, the classical four-stage Runge-Kutta integrator is invoked. For the spatial discretization, this analysis articulates the role of the primitive vector in the reconstruction of flux quantities at boundary surfaces from cell average values. The accuracy of the spatial discretization scheme is directly tied to the accuracy of the discretization of the primitive vector's derivative. To realize a stable scheme, central, forward and backward differences may be invoked (the stencils may be explicit or implicit). However, for the latter two, a stable scheme is accomplished only if the fluxes are split in the direction of the outwardly pointing normal from a cell surface. For numerical examples, we consider third-order windward biased stencils; examples are given to demonstrate many of the key attributes and deficiencies of the method.

ISSN:0920-5071    

DOI:10.1163/156939300X01490

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper several boundary integral formulations for the computation of electromagnetic fields in axisymmetric RF resonators are derived and their numerical stability is studied. The geometry may be an open (with magnetic ends) or closed cavity resonator with perfectly conducting walls or a segment of a waveguide having a dielectric window. It is found that the proper choices of integral formulation and test functions are essential in order to maintain the numerical stability of a solution as the discretization is made denser. Numerical results are presented for three simple geometries which allow analytical solutions, and as an application of the method to practical problems, the TESLA accelerating cavity and the coaxial input coupler with a ceramic window are considered. TESLA (TeV Energy Superconducting Linear Accelerator) is an international linear collider research and development project based on superconducting accelerator structures.

ISSN:0920-5071    

DOI:10.1163/156939300X01508

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this work the integral expressions of the field equations in electrostatics, magnetostatic, and electrodynamics are derived first with the aid of a scale-vector Green's theorem. The results can be interpreted by the proper sets of potential functions. For the electrodynamic case we call attention to the fact that Schelkunoff's formulas derived by applying the equivalence principle are equivalent to Stratton and Chu's. The superior nature of Franz's formulas based on the method of dyadic Green Functions is then reviewed and shown to contain the missing line integrals deliberately added by Stratton and Chu, which are also missing in Schelkunoff's formula.

ISSN:0920-5071    

DOI:10.1163/156939300X01517

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We propose highly accurate forward and inverse nonuniform fast cosine transform (NUFCT) algorithms for data sampled nonuniformly. Using the fast interpolation with regular Fourier matrices, the NUFCT algorithms requires only O(N log2N) arithmetic operations. These algorithms are then utilized in the Chebyshev pseudospectral time- domain (PSTD) method to solve Maxwell's equations on a nonuniform grid. Representing the fields and their derivatives in terms of Chebyshev polynormials, the derivatives on a nonuniform grid can be calculated with the NUFCT algorithms. The Chebyshev PSTD methods only requires π cells per wavelength on the average. Numerical results show the efficiency of the fast NUFCT and Chebyshev PSTD algorithms.

ISSN:0920-5071    

DOI:10.1163/156939300X01526

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Microwave imaging of parallel perfectly conducting cylinders using scattering data with or without the effect of random noise is considered in this paper. A novel algorithm, the real-coded genetic algorithm coupled with Newton-Kantorivitch method (RGA-NKM) is proposed to deal with it with significantly improved performance. The main idea of the RGA-NKM is to perform a Newton-Kantorivitch type search for the local optimum after the genetic operations in each genetic evolution. Numerical results and comparisons with both real-coded genetic algorithm (RGA) and Newton-Kantorivitch method (NKM) demonstrate that although the simplicity of RGA is lost, the search ability is greatly improved and the convergence is sped up significantly while those merits of RGA such as high level of robustness, versatility and insensitiveness to ill-posedness are retained.

ISSN:0920-5071    

DOI:10.1163/156939300X01535

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper describes a mode-matching method for analyzing the induced electric field in a homogeneous material sample coaxially loaded within a cylindrical cavity which is excited by a current probe. Analytical results of this method are used to compare the numerical results of an integral equation method which is presented in a companion paper published in this issue. Comparing the integral equation method and the mode-matching method, the former is more general and powerful but computationally intensive while the latter can only handle a simple geometry but it is computationally efficient.

ISSN:0920-5071    

DOI:10.1163/156939300X01544

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In the study of the heating mechanism of a material sample in an energized electromagnetic cavity, it is essential to quantify the induced electric field in a material sample placed within the cavity. In this paper, an Electric Field Integral Equation (EFIE) and a Magnetic Field Integral Equation (MFIE) for the induced fields in the material sample are derived and solved numerically. Relevant dyadic Green's functions are also derived. A complete set of vector wave functions which include both solenoidal and irrotational functions are employed to represent the induced electric field in the material sample. When solving the integral equation, due to the slow convergence rate of the dyadic Green's function, the infinite triple summation over the cavity eigenfunctions is reduced to the infinite double summation. For some material samples with specific geometries, a scheme of separating the material sample into the boundary layer region and the interior volume region is proposed. This scheme tends to improve the convergence of numerical results and also to save computation time. Numerical results agree well with theoretical estimations and analytical results generated from a mode-matching method.

ISSN:0920-5071    

DOI:10.1163/156939300X01553

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Reflective and transmitting properties of several layers of double-periodic arrays are studied. In the arrays, elements are conducting inclusions of various shapes. It is shown that in these structures all the phenomena recently found in dense wire grids with periodical defects (so called photonic band-gap structures) can be observed and explained in simple terms of inter-layer and inclusion resonances. Frequency-selective (with two and more stop bands) and polarization transformation properties of these arrays are demonstrated.

ISSN:0920-5071    

DOI:10.1163/156939300X01562

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor