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- Cheney, Margaret, et al.
(author)
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Optimal Electromagnetic Measurements
- 2000
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Reports (other academic/artistic)abstract
- We consider the problem of obtaining information about an inaccessible halfspace from electromagnetic measurements made in the accessible half-space. If the measurements are of limited precision, some scatterers will be undetectable because their scattered fields are below the precision of the measuring instrument. How can we make optimal measurements? In other words, what incident fields should we apply that will result in the biggest measurements? There are many ways to formulate this question, depending on the measuring instruments. In this paper we consider a formulation involving wavesplitting in the accessible half-space: what downgoing wave will result in an upgoing wave of greatest energy? This formulation is most natural for far-field problems. A closely related question arises in the case when we have a guess about the configuration of the inaccessible half-space. What measurements should we make to determine whether our guess is accurate? In this case we compare the scattered field to the field computed from the guessed configuration. Again we look for the incident field that results in the greatest energy difference. We show that the optimal incident field can be found by an iterative process involving time reversal “mirrors”. For band-limited incident fields and compactly supported scatterers, this iterative process converges to a sum of time-harmonic fields.
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| 3. |
- Kristensson, Gerhard, et al.
(author)
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Electromagnetic wave propagation in dispersive and complex material with time domain techniques
- 2000
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Reports (other academic/artistic)abstract
- In this paper a time domain formulation of the first and second precursor in a dispersive materials is reviewed. These precursors are determined by the susceptibility kernel of the medium, which characterizes the medium in a time domain formulation. The propagator operators of the fields are corner stones in the formulation. These operators are then approximated by a pertinent factorization procedure that defines to the first and second precursors of the medium. Wave propagation in a biisotropic medium is also treated and the early time behavior of a transient signal is addressed. Aseries of numerical examples illustrates the theory.
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| 7. |
- Kristensson, Gerhard, et al.
(author)
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Scattering from a frequency selective surface supported by a bianisotropic substrate
- 2000
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Reports (other academic/artistic)abstract
- In this paper a method for the analysis of a frequency selective surface (FSS) supported by a bianisotropic substrate is presented. The frequency selective structure is a thin metallic pattern — the actual FSS — on a plane supporting substrate. Integral representations of the fields in combination with the method of moments carried out in the spatial Fourier domain are shown to be a fruitful way of analyzing the problem with a complex substrate. This approach results in a very general formulation in which the supporting substrate can have arbitrary bianisotropic properties. The bianisotropic slab can be homogeneous, stratified, or it can have continuously varying material parameter as a function of depth. The analysis presented in this paper is illustrated in a series of numerical examples. Results for isotropic, anisotropic and bianisotropic substrates are given.
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