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Träfflista för sökning "swepub ;srt2:(1990-1994);pers:(Kristensson Gerhard)"

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

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11.
  • Karlsson, Anders, et al. (författare)
  • Wave splitting and imbedding equations for a spherically symmetric dispersive medium
  • 1991
  • 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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12.
  • Karlsson, Anders, et al. (författare)
  • Wave splitting in the time domain for a radially symmetric geometry
  • 1990
  • Ingår i: Wave Motion. - : Elsevier BV. - 0165-2125. ; 12:3, s. 197-211
  • 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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13.
  • Kristensson, Gerhard (författare)
  • Direct and inverse scattering problems in dispersive media-Green's functions and invariant imbedding techniques
  • 1990
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Transient electromagnetic wave propagation in a dispersive medium is reviewed. The medium is assumed to be 1) linear, 2) invariant to time translations, 3) causal, 4) continuous, and 5) isotropic. The constitutive relations are then uniquelyrepresen ted bya Riemann-Stieltjes integral in the time variable. The kernel in this convolution is the susceptibilityk ernel. Two explicit examples of mathematical models of the susceptibilityk ernel are given. The medium treated in this paper is assumed to varyonlywith depth. In the direct problem the reflection and transmission data are computed. The inverse scattering problem is to find the susceptibilityk ernel from known reflexion data. It is, thus, a problem of finding a function depending on the time variable. In the spatiallyhomogeneous case the inverse scattering problem is solved from reflexion data bysolving a Volterra integral equation of the second kind. This inverse problem is therefore well-posed and easyto solve.
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16.
  • Kristensson, Gerhard, et al. (författare)
  • Scattering of transient electromagnetic waves in reciprocal bi-isotropic media
  • 1992
  • Ingår i: Journal Electromagnetic Waves and Applications. - 1569-3937. ; 6:11, s. 1517-1535
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper propagation of transient electromagnetic waves in a reciprocal bi-isotropic medium is presented. The constitutive relations are convolution integrals with two susceptibility kernels that model the medium. The propagation problem is solved by the introduction of a wave-splitting technique. This wave-splitting is used to solve the propagation problem using either an imbedding approach or a Green's function technique. In particular, the scattering problem of an electromagnetic wave that impinges normally on a slab of finite or infinite extent is solved. The slab is assumed to be inhomogeneous with respect to depth. The scattering problem consists of finding the reflected and the transmitted fields and the generic quantities are the reflection and the transmission kernels of the medium. Explicit expressions for the rotation and the attenuation of the wave front is presented for the inhomogeneous slab. In the special case of a homogeneous infinite slab it is proved that the reflection kernel satisfies a nonlinear Volterra equation of the second kind, very suitable for numerical calculations. It is also proved that no cross polarization contribution appears for the homogeneous slab. Several numerical computations illustrate the analysis.
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17.
  • Kristensson, Gerhard, et al. (författare)
  • Scattering of transient electromagnetic waves in reciprocal bi-isotropic media
  • 1991
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • In this paper propagation of transient electromagnetic waves in a reciprocal bi-isotropic medium is presented. The constitutive relations are convolution integrals with two susceptibility kernels that model the medium. The propagation problem is solved by the introduction of a wave-splitting technique. This wave-splitting is used to solve the propagation problem using either an imbedding approach or a Green function technique. In particular, the scattering problem of an electromagnetic wave that impinges normally on a slab of finite or infinite extent is solved. The slab is assumed to be inhomogeneous with respect to depth. The scattering problem consists of finding the reflected and the transmitted fields and the generic quantities are the reflection and the transmission kernels of the medium. Explicit expressions for the rotation and the attenuation of the wave front is presented for the inhomogeneous slab. In the special case of a homogeneous infinite slab it is proved that the reflection kernel satisfies a non-linear Volterra equation of the second kind, very suitable for numerical calculations. It is also proved that no cross polarization contribution appears for the homogeneous slab. Several numerical computations illustrate the analysis.
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18.
  • 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. - 0075-8450. - 3540571957 ; 422, s. 112-125
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)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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19.
  • Kristensson, Gerhard, et al. (författare)
  • The inverse scattering problem for a homogeneous bi-isotropic slab using transient data
  • 1992
  • Rapport (övrigt vetenskapligt/konstnärligt)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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20.
  • Kristensson, Gerhard (författare)
  • Time domain inversion techniques for electromagnetic scattering problems
  • 1990
  • Rapport (övrigt vetenskapligt/konstnärligt)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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  • Resultat 11-20 av 29

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