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  • 1. Aksimsek, Sinan
    et al.
    Cinar, Gökhan
    Nilsson, Börje
    Linnaeus University, Faculty of Technology, Department of Mathematics.
    Nordebo, Sven
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    TEM wave scattering by a step discontinuity on the outer wall of a coaxial waveguide2013In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 61, no 8, p. 2783-2791Article in journal (Refereed)
    Abstract [en]

    In this paper, the propagation of TEM waves along a coaxial waveguide with a step discontinuity on its outer wall is investigated rigorously by applying the direct Fourier transform and reducing the problem into the solution of a modified Wiener–Hopf equation. The solution for the field terms are determined in terms of an infinite number of unknown coefficients, which satisfy an infinite set of linear algebraic equations. These equations are solved numerically and the effect of area ratio is presented graphically at the end of the analysis. The same problem is also analyzed by applying the mode-matching technique and the results of the two approaches are compared. It is observed numerically that the Wiener–Hopf technique provides a better convergence than the mode-matching technique.

  • 2.
    Engström, Christian
    ETH Zurich, Switzerland.
    On a method to reduce uncertainties in bulk property measurements of two-component composites2010In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 58, no 2, p. 434-439Article in journal (Refereed)
    Abstract [en]

    For two-component composites, we address the inverse problem of estimating the structural parameters and decrease measurement errors in bulk property measurements. A measurement of the effective permittivity at one frequency gives microstructural information about the composite that is used in cross-property bounds to estimate the effective permittivity at other frequencies. We use this information and inverse bounds on microstructural parameters to tighten error bars on permittivity measurements at microwave frequencies. The method can be used in the design of random and periodic composite materials for a large variety of applications. We apply the method to a composite material used in radar applications.

  • 3.
    Kaufmann, Thomas
    et al.
    ETH Zurich, Switzerland.
    Engström, Christian
    ETH Zurich, Switzerland.
    Fumeaux, Christoph
    University of Adelaide, Australia.
    Vahldieck, Rudinger
    ETH Zurich, Switzerland.
    Eigenvalue-analysis and longtime-stability of resonant structures for the meshless radial point interpolation method in time-domain2010In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 58, no 12, p. 3399-3408Article in journal (Refereed)
    Abstract [en]

    A meshless collocation method based on radial basis function (RBF) interpolation is presented for the numerical solution of Maxwell's equations. RBFs have attractive properties such as theoretical exponential convergence for increasingly dense node distributions. Although the primary interest resides in the time domain, an eigenvalue solver is used in this paper to investigate convergence properties of the RBF interpolation method. The eigenvalue distribution is calculated and its implications for longtime stability in time-domain simulations are established. It is found that eigenvalues with small, but nonzero, real parts are related to the instabilities observed in time-domain simulations after a large number of time steps. Investigations show that by using global basis functions, this problem can be avoided. More generally, the connection between the high matrix condition number, accuracy, and the magnitude of nonzero real parts is established.

  • 4.
    Nordebo, Sven
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Cinar, Gökhan
    Gebze Institute of Technology, Turkey.
    Gustafsson, Stefan
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Nilsson, Börje
    Linnaeus University, Faculty of Technology, Department of Mathematics.
    Dispersion modeling and analysis for multilayered open coaxial waveguides2015In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 63, no 6, p. 1791-1799Article in journal (Refereed)
    Abstract [en]

    This paper presents a detailed modeling and analysis regarding the dispersion characteristics ofmultilayered open coaxial waveguides or cables. The electromagnetic model is based on a layer recursive computation of axial-symmetric fields in connection with a magnetic frill generator excitation that can be calibrated to the current measured at the input of the cable. The layer recursive formulation enables a stable and efficient numerical computation of the related dispersion functions, as well as a detailed analysis regarding the analytic and asymptotic properties of the associated determinants. Modal contributions as well as the contribution from the associated branch-cut (nondiscrete radiating modes) are defined and analyzed. Measurements and modeling of pulse propagation on an 82-km-long HVDC power cable are presented as a concrete example. In this example, it is concluded that the contribution from the dominating axial-symmetric transverse magnetic mode is sufficient, and that the contribution from the branch-cut is negligible for all practical purposes, and in particular if the exterior domain is lossy. The main contribution of this paper is to provide the necessary modeling and analysistools for a quantitative study of these phenomena.

  • 5.
    Vakili, Iman
    et al.
    Lund Univ.
    Gustafsson, Mats
    Lund Univ.
    Sjöberg, Daniel
    Lund Univ.
    Seviour, Rebecca
    Lund Univ.
    Nilsson, Martin
    Lund Univ.
    Nordebo, Sven
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Sum Rules for Parallel-Plate Waveguides: Experimental Results and Theory2014In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 62, no 11, p. 2574-2582Article in journal (Refereed)
    Abstract [en]

    An experimental approach to investigate the forward scattering sum rule for periodic structures is presented. This approach allows an upper bound on the total cross section integrated over a bandwidth from a simple static problem to be found. Based on energy conservation, the optical theorem is used to construct a relation between the total cross section and the forward scattering of periodic structures as well as single scatterers inside a parallel-plate waveguide. Dynamic measurements are performed using a parallel-plate waveguide and a parallel-plate capacitor is utilized to find the static polarizability. Convex optimization is introduced to identify the total cross section in the dynamic measurements and estimate an optimal lower bound on the polarizability for objects. The results show that the interactions between the electromagnetic field and an object over all wavelengths are given by the static polarizability of the object.

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