摘要:

The exact lateral electromagnetic pulse generated by a vertical dipole excited by a Gaussian pulse is derived. A comparison with the previously derived approximate formula shows that the latter gives the correct field at all radial distances except for the nonappearance of the relatively small second pulse. Corresponding approximate formulas are derived for the electric field of a horizontal dipole. These should give the correct field except for the nonappearance of the small second pulse in some components.

ISSN:0920-5071    

DOI:10.1163/156939389X00241

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Using the studies realized by Meinke [1], Tisher and Yee [2] and Laura [3] to determine by conformal mapping the cutoff frequencies for TM or TE waves in waveguides of very general cross-section, we show that it is possible to generalize it to periodic waveguides with EH waves [4]. For rectangular overdimensioned waveguides with sinusoidal or rectangular corrugations, the comparison of the theoretical and experimental results is satisfactory when corrugations are relatively large compared with wavelength.

ISSN:0920-5071    

DOI:10.1163/156939389X00250

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Using a set of surface integral equations together with the moment method, we develop a numerical algorithm so that one can calculate the response of the induction logging tool in an arbitrarily shaped borehole. The integral equations are derived whereby the small formation signal can be calculated in the presence of a large direct signal. The results of a circular borehole with an eccentered tool are presented and compared with the results from other approaches. The responses of a horizontal magnetic dipole in an elliptical invasion zone and an elliptical borehole are obtained. The results show that horizontal magnetic dipoles can be used to detect asymmetry in an invasion profile and a borehole.

ISSN:0920-5071    

DOI:10.1163/156939389X00269

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Kirchhoff's surface integral representation for the solution of the wave equation, also commonly referred to as the Huygens' principle, is presently considered for the case of time dependent (i.e., moving) surfaces. This is motivated by problems involving moving sources and scatterers prescribed on moving surfaces. A general formulation and discussion of simple examples are given here. The surface integral representation for the solution of the scalar and vector wave equations, for harmonic and arbitrary time dependence, are used as a starting point. The extension of these integrals to the case of time dependent surfaces and its validity are discussed. In general one can always extend the representations to arbitrarily moving surfaces, but the explicit integration with respect to the retarded time relevant to the sources on the moving surface cannot be performed in general. In the special case of motion of surface elements in the direction of the normal, it is shown that the integration is feasible. The retarded time involved in moving surface integrals is shown to be closely related to the well-known Doppler frequency shift. Using Special Relativity, operational forms are found for these integrals, relating the field measured in the laboratory frame of reference to the source fields defined in the co-moving frame of reference of the elements on the moving surface.

ISSN:0920-5071    

DOI:10.1163/156939389X00278

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The eigenmode problem for multilayered structures with coplanar or non-coplanar strips is analysed using the space domain Green's dyadic of these structures as the kernel of an integral equation. The integral equation is solved using the method of moments combined with point-matching. The calculation of the Green's dyadic starts in the spectral domain. First, an efficient solution technique is presented to determine the spectral Green's dyadic. Special attention is then devoted to its behaviour for large values of the Fourier variable and to the contribution of this asymptotic part to the space domain Green's dyadic. The behaviour of the fields in the vicinity of the excitation is determined explicitly. The method is illustrated by two typical examples.

ISSN:0920-5071    

DOI:10.1163/156939389X00287

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939389X00296

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor