| 1. |
- Karlsson, Anders, et al.
(författare)
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Transient wave propagation in gyrotropic media
- 1992
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Ingår i: Invariant inbedding and inverse problems. - 0898713056 ; , s. 77-89
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this paper transient electromagnetic wave propagation in an inhomogeneous, cold plasma is considered. It is assumed that a constant magnetic induction is present and that the plasma is spatially inhomogeneous in the direction of the magnetic induction. Losses in the plasma are modeled with a collision frequency ν. The direct problem, which is to calculate the reflected and transmitted responses of the plasma, is considered in this paper. Special attention is paid to the precursor effects in the plasma and several examples of precursor effects in an inhomogeneous plasma are showed.
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| 2. |
- Karlsson, Anders, et al.
(författare)
-
Wave splitting and imbedding equations for a spherically symmetric dispersive medium
- 1992
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Ingår i: Invariant inbedding and inverse problems. - 0898713056 ; , s. 103-113
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The direct problem of time dependent electromagnetic scattering in the dispersive sphere is solved by a wave splitting technique. The electric field is expanded in a series involving vector spherical harmonics, leading to a system of wave equations for each term. These systems are reduced to scalar wave equations for each term, which are solved via reflection operators. Some preliminary numerical results are presented.
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| 3. |
- Karlsson, Anders, et al.
(författare)
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Constitutive relations, dissipation and reciprocity for the Maxwell equations in the time domain
- 1992
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Ingår i: Journal Electromagnetic Waves and Applications. - 1569-3937. ; 6:5-6, s. 537-551
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Tidskriftsartikel (refereegranskat)abstract
- The main goal of this paper is to establish general constitutive relations for the electromagnetic fields EBAR, DBAR, BBAR, and HBAR in a time domain setting. The four basic assumptions of the medium are linearity, invariance to time translations, causality, and continuity. These four assumptions imply that the constitutive relations are convolutions of the Riemann-Stieltjes type. A review of the classification of media in bianisotropic, biisotropic, anisotropic, and isotropic media, respectively, is made. Dissipation and reciprocity are defined and the constraints these concepts make on the constitutive relations are analyzed. Furthermore, an appropriate form of time reversal and functions of positive type are introduced and some consequences of these concepts are showed.
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| 4. |
- Karlsson, Anders, et al.
(författare)
-
Transient wave propagation in gyrotropic media
- 1990
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper transient electromagnetic wave propagation in an inhomogeneous, cold plasma is considered. It is assumed that a constant magnetic induction is present and that the plasma is spatially inhomogeneous in the direction of the magnetic induction. Losses in the plasma are modeled with a collision frequency ν. The direct problem, which is to calculate the reflected and transmitted responses of the plasma, is considered in this paper. Special attention is paid to the precursor effects in the plasma and several examples of precursor effects in an inhomogeneous plasma are showed.
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| 5. |
- Karlsson, Anders, et al.
(författare)
-
Wave splitting and imbedding equations for a spherically symmetric dispersive medium
- 1991
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The direct problem of time dependent electromagnetic scattering in the dispersive sphere is solved by a wave splitting technique. The electric field is expanded in a series involving vector spherical harmonics, leading to a system of wave equations for each term. These systems are reduced to scalar wave equations for each term, which are solved via reflection operators. Some preliminary numerical results are presented.
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| 6. |
- Karlsson, Anders, et al.
(författare)
-
Wave splitting in the time domain for a radially symmetric geometry
- 1990
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Ingår i: Wave Motion. - : Elsevier BV. - 0165-2125. ; 12:3, s. 197-211
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Tidskriftsartikel (refereegranskat)abstract
- A decomposition of the field of the wave equation in three dimensions is suggested. This wave splitting decomposes the field into two components such that in free space simple propagation properties are obtained. The inhomogeneous region is assumed to have a phase velocity variation that varies only in the radial coordinate r from the origin. The suggested wave splitting is a generalization of the wave splitting concept in one spatial dimension. Specifically, the propagation properties in free space in the three-dimensional wave splitting are very analogous to the corresponding propagation properties in free space in one dimension. The three-dimensional decomposition is illustrated in an example of scattering by a sound-soft sphere of radius a.
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| 7. |
- Malmqvist, Lennart, et al.
(författare)
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Electromagnetic fields in boreholes-measurements and theory in three dimensions
- 1990
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A comparison between experimental measurements of the electromagnetic field in boreholes and a mathematical model is made. The transmitting antenna is a rectangular wire loop on the ground and the three orthogonal components of the magnetic field are measured below the ground in the borehole. In the mathematical model the ground is assumed to be a stratified half space with a rectangular wire antenna on the ground. Excellent agreement was found between the experimental results and the theoretical ones in most cases and where deviations were found, the assumption of a stratified ground was inaccurate due to present conductive inhomogeneities. The method presented in this paper is capable of determining an ore body within a radius of 100 m from the borehole. The position (direction and distance) of the target can be estimated from the measurements in the borehole. The impact on the economical effectiveness of a drilling programme is considerable when a prediction of the location of additional boreholes can be made. In the case of reconnaissance drilling of a geological structure or trend the distance between adjacent boreholes can be considerably enlarged.
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