| 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)
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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. |
- Kristensson, Gerhard, et al.
(författare)
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Time domain inversion techniques for electromagnetic scattering problems
- 1992
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Ingår i: Invariant imbedding and inverse problems. - 0898713056 ; , s. 1-29
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Bokkapitel (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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| 4. |
- Fridén, Jonas, et al.
(författare)
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Transient Electromagnetic Wave Propagation in Anisotropic Dispersive Media
- 1992
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper transient electromagnetic wave propagation in a stratified, anisotropic, dispersive medium is considered. Specifically, the direct scattering problem is addressed. The dispersive, anisotropic medium is modeled by constitutive relations (a 3 × 3 matrix-valued susceptibility operator)con taining time convolution integrals. In the general case, nine different susceptibility kernels characterize the medium. An incident plane wave impinges obliquely on a finite slab consisting of a stratified anisotropic medium. The scattered fields are obtained as time convolutions of the incident field with the scattering kernels. The scattering (reflection and transmission)k ernels are uniquely determined by the slab and are independent of the incident field. The scattering problem is solved by a wave splitting technique. Two different methods to determine the scattering kernels are presented; an imbedding and a Green functions approach. Explicit analytic expressions of the wave front are given for a special class of media. Some numerical examples illustrate the analysis.
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| 5. |
- 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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| 6. |
- Kristensson, Gerhard, et al.
(författare)
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Scattering of transient electromagnetic waves in reciprocal bi-isotropic media
- 1992
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Ingår i: Journal Electromagnetic Waves and Applications. - 1569-3937. ; 6:11, s. 1517-1535
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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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| 7. |
- Kristensson, Gerhard, et al.
(författare)
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The inverse scattering problem for a homogeneous bi-isotropic slab using transient data
- 1992
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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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| 8. |
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| 9. |
- Kristensson, Gerhard, et al.
(författare)
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Transient wave propagation in reciprocal bi-isotropic media at oblique incidence
- 1992
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper a new wave splitting is suggested that simplifies the analysis of wave propagation in reciprocal bi-isotropic media. Two different methods to solve the scattering problem are analyzed; the invariant imbedding and the Green function approach. The medium is modeled by constitutive relations in the time domain (time convolutions) and the slab is assumed to be inhomogeneous with respect to the depth. It is showed that the cross-polarized contribution to the reflected field at normal incidence is zero for the general reciprocal inhomogeneous slab. Moreover, the rotation and the attenuation of the wave front are calculated explicitly in the general inhomogeneous slab case. Special attention is paid to normal incidence and to the homogeneous semi-infinite medium.
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