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Sökning: LAR1:lu > Sjöberg Daniel > Lunds universitet > Rapport > (2010-2011)

  • Resultat 1-7 av 7
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  • Gustafsson, Mats, et al. (författare)
  • Optical theorem and forward scattering sum rule for periodic structures
  • 2011
  • Rapport (övrigt vetenskapligt)abstract
    • Based on energy conservation, an optical theorem is constructed for a slab having an arbitrary periodic microstructure in a plane. A sum rule for low pass structures is derived using analytic properties of Herglotz functions based on causality and passivity. The sum rule relates the extinction cross section to the static polarizability per unit cell, and quantifies the interaction between the slab and electromagnetic fields possible over all wavelengths. The results are illustrated with several numerical and experimental examples.
  • Gustafsson, Mats, et al. (författare)
  • Physical bounds and sum rules for high-impedance surfaces
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • High-impedance surfaces are artificial surfaces synthesized from periodic structures. The high impedance is useful as it does not short circuit electric currents and reflects electric fields without phase shift. Here, a sum rule is presented that relates frequency intervals having high impedance with the thickness of the structure. The sum rule is used to derive physical bounds on the bandwidth for high-impedance surfaces. Numerical examples are used to illustrate the result, and show that the physical bounds are tight.
  • Gustafsson, Mats, et al. (författare)
  • Sum rules and physical bounds on passive metamaterials
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • Frequency dependence of the permittivity and permeability is inevitable in metamaterial applications such as cloaking and perfect lenses. In this paper, Herglotz functions are used as a tool to construct sum rules from which we derive physical bounds suited for metamaterial applications, where the material parameters are often designed to be negative or near zero in the frequency band of interest. Several sum rules are presented that relate the temporal dispersion of the material parameters with the difference between the static and instantaneous parameter values, which are used to give upper bounds on the bandwidth of the application. This substantially advances the understanding of the behavior of metamaterials with extraordinary material parameters, and reveals a beautiful connection between properties in the design band (finite frequencies) and the low- and high-frequency limit.
  • Larsson, Christer, et al. (författare)
  • Waveguide measurements of the permittivity and permeability at temperatures up to 1000 C
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • This paper describes a method to measure the permittivity and the permeability at temperatures from room temperature up to 1000 C using a single rectangular waveguide. The hardware design of the setup that can handle these temperatures and the procedure that is required to correct for the thermal expansion is developed. This includes the sample displacement, the displacement of the calibration reference planes, the thermal expansion of the waveguide and the gap between the sample and the waveguide wall. Measurements on Macor\textregistered and NiZn Ferrite samples are performed in order to evaluate the performance of the setup and the procedure that is used to determine the permittivity and permeability from the measured S-parameters.
  • Sjöberg, Daniel, et al. (författare)
  • Cramér-Rao bounds for determination of permittivity and permeability in slabs
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • We compute the Cramér-Rao lower bounds for determination of isotropic permittivity and permeability in slabs using scattering data such as reflection and transmission coefficients. Assuming only the fundamental mode is propagating in the slab, the results are formally the same regardless if the slab is in free space, or inside a rectangular or coaxial waveguide. The bounds depend only on signal quality and not the actual inversion method used, making them suitable to evaluate a particular measurement setup. The results are illustrated with several measurements in a rectangular waveguide setting.
  • Sjöberg, Daniel, et al. (författare)
  • Physical bounds on the all-spectrum transmission through periodic arrays: oblique incidence
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • The performance of a low-pass screen designed to block electromagnetic waves in a stop-band is shown to have an upper bound defined by the static electric and magnetic polarizability per unit area of the screen. The bound is easy to calculate for all angles of incidence and polarizations, and applies regardless of how complicated the screen's microstructure is. For a homogeneous dielectric sheet the bound for TM polarization is more restrictive than the bound for TE, but this is not generally true for a screen with microstructure. The results are verified by measurements and simulations of oblique transmission through an array of split ring resonators, printed on a dielectric substrate.
  • Sjöberg, Daniel, et al. (författare)
  • Realization of a matching region between a radome and a ground plane
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • In order to reduce the monostatic signature of the junction between a radome and the metallic structure to which it is attached, a tapered resistive sheet can be used. In this paper, we describe an easy method to realize this tapering using geometric variations on a subwavelength scale, with a significant reduction of the number of processing steps as a result.
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  • Resultat 1-7 av 7
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övrigt vetenskapligt (7)
Gustafsson, Mats, (5)
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Vakili, Iman, (1)
Bayer Keskin, Sena E ... (1)
Elmkvist, Lisa (1)
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