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Träfflista för sökning "WFRF:(Kristensson Gerhard) "

Sökning: WFRF:(Kristensson Gerhard)

  • Resultat 1-10 av 281
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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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4.
  • 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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8.
  • Kristensson, Elias, et al. (författare)
  • Physical explanation of the SLIPI technique by the large scatterer approximation of the RTE
  • 2017
  • Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - Elsevier. - 0022-4073. ; 189, s. 112-125
  • Tidskriftsartikel (refereegranskat)abstract
    • Visualizing the interior of a turbid scattering media by means light-based methods is not a straightforward task because of multiple light scattering, which generates image blur. To overcome this issue, a technique called Structured Laser Illumination Planar Imaging (SLIPI) was developed within the field of spray imaging. The method is based on a ‘light coding’ strategy to distinguish between directly and multiply scattered light, allowing the intensity from the latter to be suppressed by means of data post-processing. Recently, the performance of the SLIPI technique was investigated, during which deviations from theoretical predictions were discovered. In this paper, we aim to explain the origin of these deviations, and to achieve this end, we have performed several SLIPI measurements under well-controlled conditions. Our experimental results are compared with a theoretical model that is based on the large scatter approximation of the Radiative Transfer Equation but modified according to certain constraints. Specifically, our model is designed to (1) ignore all off-axis intensity contributions, (2) to treat unperturbed- and forward-scattered light equally and (3) to accept light to scatter within a narrow forward-cone as we believe these to the rules governing the SLIPI technique. The comparison conclusively shows that optical measurements based on scattering and/or attenuation in turbid media can be subject to significant errors if not all aspects of light-matter interactions are considered. Our results indicate, as were expected, that forward-scattering can lead to deviations between experiments and theoretical predictions, especially when probing relatively large particles. Yet the model also suggests that the spatial frequency of the superimposed ‘light code’ as well as the spreading of the light-probe are important factors one also needs to consider. The observed deviations from theoretical predictions could, however, potentially be exploited to assess particle size
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9.
  • Alayon Glazunov, Andres, et al. (författare)
  • Branch cross-correlation in presence of spatially selective interference Expressed in Terms of the spherical vector wave expansion of the electromagnetic field
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • Abstract in Undetermined In this paper we present an analysis of the cross-correlation coe±cient between signals at two antenna branches (ports) in the presence of spatially selective interference and additive white gaussian noise. More specifically, we look at a ±45 slanted polarization diversity arrangement, which is rotated around the axis perpendicular to the plane containing the antennas. Results are provided as a function of the rotation angle. The analysis is based on the spherical vector wave multi-pole expansion of both the field impinging on the antennas and the antenna radiation properties.
10.
  • Alayon Glazunov, Andres, et al. (författare)
  • On the mean effective gain expressed in terms of the spherical vector wave expansion of the electromagnetic field
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • The mode expansion o®ers a general framework for the analysis of the interaction between antennas andpropagation channels. In this paper, the Mean E®ective Gain (MEG) of an antenna is expressed in termsof the spherical vector wave expansion of the electromagnetic ¯eld. An explicit expression of the MEG isprovided as a function of the normalized average power of modes excited in the propagation channel andthe correlation between the channel modes due to the polarization and spatial selectivity of plane wavesimpinging at the antenna.
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