摘要:

Using a method based on the asymptotic expansion of the field inside a homogeneous dielectric body in inverse powers of N, where N is the complex refractive index, a boundary condition is developed accurate to the third order in 1/N applicable at the surface γ = constant of the body, where α, β, γ are orthogonal curvilinear coordinates. In contrast to the standard (first order) condition, the boundary condition involves tangential field derivatives through the second order, and is an example of a second order generalized impedance condition. The superior accuracy that it provides is demonstrated, and the result has important consequences in connection with absorbing boundary conditions used to terminate the computational domain in a finite element or finite difference solution of the wave equation.

ISSN:0920-5071    

DOI:10.1163/156939395X00019

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

New equations are presented which give the terminal velocity of water droplets in three physically distinct drag regimes explicitly as functions of equivalent drop radius and height in a standard atmosphere. It is shown that at h = 0 , the expressions give results which agree with Gunn and Kinzer's terminal velocity measurements with an overall divergence less than the measurement uncertainty of the data. Results are also compared with the semi-empirical formulations of Beard and shown to be in good agreement at all drop sizes 0.25 r03500 μm and heights -1.5 h 5 km in the atmosphere.

ISSN:0920-5071    

DOI:10.1163/156939395X00028

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The influence of dielectric objects on electromagnetic fields is an important consideration in many engineering problems. In some applications, the scattering from dielectric objects for a known incident field is of interest. In other situations where dielectric objects interact with radiators - such as biological tissue near a wireless transceiver or a dielectric loaded antenna - the resulting input impedance, far-field radiation and power absorption characteristics are important quantities to determine. In this work an integral equation approach is used to solve these problems for which the method of moments is applied to facilitate a numerical solution. A comprehensive computer program was developed that handles both scattering and radiation problems. With the computer program both dipole and superquadric loop antennas can be modeled which have any arbitrary relative location and orientation to dielectric bodies of interest. The implementation is verified by comparison with finite-difference time-domain results and available measured data for both a scattering and radiation problem involving dielectric objects. It is then used to study some diverse situations which would be difficult to handle with standard Cartesian grid finite-difference time-domain, including: monostatic radar cross section of a dielectric slab with various conductivities; dipole and superquadric loop radiators printed on a dielectric substrate; and loop antennas in close proximity to a model of the human head.

ISSN:0920-5071    

DOI:10.1163/156939395X00037

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939395X00046

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Experimental and theoretical investigations have been carried out to determine the effect of the interface on the back scattered field of a loop metallic antenna and an oscillator with a nonlinear local load (in the form of a semiconductor diode) placed in the dielectric near the boundary. The growth of the scattered signal level is noted at the limits of the quasi-static zone with an increase in the distance between the nonlinear scatterer and the boundary. With a further increase in this distance, the indicated dependence has an oscillating characteristic.

ISSN:0920-5071    

DOI:10.1163/156939395X00055

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We obtain an exact solution for a circular wire loop, carrying a non-uniform current, located above a layered half-space The method, while straight-forward, allows for both T.E. and T.M. electromagnetic fields. The T.M. fields would not be present if the current distribution was uniform. As a consequence of the nonuniformity, vertically polarized radio ground waves may be excited and such could be a source of unwanted interference. Such loop sources are employed in geophysical probing schemes and it is suggested that the most desirable configuration would be if the vertical magnetic field is measured at the center of the horizontal loop. The contributions of the higher spatial harmonics of the current in the loop vanishes in this case. On the other hand one may wish to employ such a source loop, lying on the earth's surface, to provide a useable radio ground wave for point-to-point communication over poorly conducting terrain such as in polar regions.

ISSN:0920-5071    

DOI:10.1163/156939395X00064

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Parallel computations of an integral equation technique in conjunction with a Method of Moments (MoM) is introduced, in examining electromagnetic illumination of electrically large scatterers. To this end, the electromagnetic scattering of an incident wave illuminating an electrically large conducting rectangular plate of infinitesimal thickness is analyzed. An integral equation is derived in terms of the conductivity currents induced on the plate surface, which is solved by employing entire domain Galerkin technique, with Chebyshev type basis functions. The resulting algorithm parallelization enables extension of the proposed methodology above the resonance region. Numerical results are computed for several scatterer sizes and excitation source types, with significant near-linear speedups.

ISSN:0920-5071    

DOI:10.1163/156939395X00073

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this paper, an algorithm for computation of the scattered fields from three dimensional inhomogeneous dielectric scatterers is presented. In this method, the Galerkin's testing formulation of an integral equation for 3D electromagnetic (EM) fields is represented by a multi-input and multi-output linear system with known kernels. On a regular grid with rooftop basis functions, the kernels are discretized and accurately evaluated. Furthermore they are represented by Toeplitz matrices which dramatically reduces the storage and computational complexity in solving for the scattered fields. Also, the kernels are independent of the scattering configuration and the incident waves. For a given frequency, they can be evaluated once and for all. The biconjugate gradient (BCG) algorithm combined with fast Fourier transform (FFT) is applied to solve the discrete linear system iteratively. The memory required for this algorithm is of order N, and the computational complexity of the BCG process costs order N log N operations per iteration, where N is the number of 3D unknowns. Unlike previous approaches, no approximation is made when FFT is used to accelerate the matrix-vector multiplication.

ISSN:0920-5071    

DOI:10.1163/156939395X00082

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939395X00091

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939395X00109

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor