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Sökning: swepub > (1990-1994) > Kristensson Gerhard > Bokkapitel

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1.
  • Karlsson, Anders, et al. (författare)
  • Transient wave propagation in gyrotropic media
  • 1992
  • Ingår i: Invariant inbedding and inverse problems. - SIAM. - 0-89871-305-6 ; s. 77-89
  • Bokkapitel (övrigt vetenskapligt)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
  • Ingår i: Invariant inbedding and inverse problems. - SIAM. - 0-89871-305-6 ; s. 103-113
  • Bokkapitel (övrigt vetenskapligt)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.
  • Kristensson, Gerhard, et al. (författare)
  • Time domain inversion techniques for electromagnetic scattering problems
  • 1992
  • Ingår i: Invariant imbedding and inverse problems. - SIAM. - 0-89871-305-6 ; s. 1-29
  • Bokkapitel (övrigt vetenskapligt)abstract
    • This paper presents a review of and a comparison between two different methods to solve an inverse scattering problem in the time domain. The problem is that of propagation of transient electromagnetic waves in spatially inhomogeneous slabs of finite length. The permittivity and conductivity profiles are assumed to vary only with depth and the scattering problem is thus onedimensional. Several algorithms to solve the direct and inverse scattering problems for continuous and discontinuous permittivity profiles are suggested. Some of these algorithms have not been published before. The aim of this paper is to compare and review these methods. More specifically, the numerical performance of the invariant imbedding approach (layer-stripping)and the Green functions formulation (downward continuation)is compared. Some new results based upon time reversal techniques for a lossless slab are presented in an appendix.
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5.
  • Kristensson, Gerhard, et al. (författare)
  • The inverse scattering problem for a homogeneous bi-isotropic slab using transient data
  • 1993
  • Ingår i: Inverse problems in mathematical physics / Lecture notes in physics. - Springer-Verlag GmbH. - 0075-8450. - 3-540-57195-7 ; 422, s. 112-125
  • Bokkapitel (övrigt vetenskapligt)abstract
    • Transient wave propagation in a finite bi-isotropic slab is treated. The incident field impinges normally on the slab, which can be inhomogeneous wrt depth. Dispersion and bi-isotropy are modeled by time convolutions in the constitutive relations. Outside the slab the medium is assumed to be homogeneous, non-dispersive and isotropic, and such that there is no phase velocity mismatch at the boundaries of the slab. Two alternative methods of solution to the propagation problem are given—the imbedding method and the Green function approach. The second method is used to solve the inverse problem and the first to generate synthetic data. The inverse scattering problem is to reconstruct the four susceptibility kernels of the medium using a set of finite time trace of reflection and transmission data.
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