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Träfflista för sökning "hsv:(TEKNIK OCH TEKNOLOGIER) hsv:(Elektroteknik och elektronik) ;pers:(Nordebo Sven)"

Sökning: hsv:(TEKNIK OCH TEKNOLOGIER) hsv:(Elektroteknik och elektronik) > Nordebo Sven

  • Resultat 1-10 av 236
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1.
  • Gustafsson, Stefan, et al. (författare)
  • Electromagnetic dispersion modeling and measurements for HVDC power cables
  • 2014
  • Ingår i: IEEE Transactions on Power Delivery. - : IEEE Press. - 0885-8977 .- 1937-4208. ; 29:6, s. 2439-2447
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper provides a general framework for electromagnetic (EM) modeling, sensitivity analysis, computation, and measurements regarding the wave propagation characteristics of high-voltage direct-current (HVDC) power cables. The modeling is motivated by the potential use with transient analysis, partial-discharge measurements, fault localization and monitoring, and is focused on very long (10 km or more) HVDC power cables with transients propagating in the low-frequency regime of about 0-100 kHz. An exact dispersion relation is formulated together with a discussion on practical aspects regarding the computation of the propagation constant. Experimental time-domain measurement data from an 80-km-long HVDC power cable are used to validate the electromagnetic model, and a mismatch calibration procedure is devised to account for the connection between the measurement equipment and the cable. Quantitative sensitivity analysis is devised to study the impact of parameter uncertainty on wave propagation characteristics. The sensitivity analysis can be used to study how material choices affect the propagation characteristics, and to indicate which material parameters need to be identified accurately in order to achieve accurate fault localization. The analysis shows that the sensitivity of the propagation constant due to a change in the conductivity in the three metallic layers (the inner conductor, the intermediate lead shield, and the outer steel armor) is comparable to the sensitivity with respect to the permittivity of the insulating layer. Hence, proper modeling of the EM fields inside the metallic layers is crucial in the low-frequency regime of 0-100 kHz.
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2.
  • Ivanenko, Yevhen, et al. (författare)
  • Quasi-Herglotz functions and convex optimization
  • 2020
  • Ingår i: Royal Society Open Science. - : The Royal Society Publishing. - 2054-5703. ; 7:1, s. 1-15
  • Tidskriftsartikel (refereegranskat)abstract
    • We introduce the set of quasi-Herglotz functions and demonstrate that it has properties useful in the modelling of non-passive systems. The linear space of quasi-Herglotz functions constitutes a natural extension of the convex cone of Herglotz functions. It consists of differences of Herglotz functions and we show that several of the important properties and modelling perspectives are inherited by the new set of quasi-Herglotz functions. In particular, this applies to their integral representations, the associated integral identities or sum rules (with adequate additional assumptions), their boundary values on the real axis and the associated approximation theory. Numerical examples are included to demonstrate the modelling of a non-passive gain medium formulated as a convex optimization problem, where the generating measure is modelled by using a finite expansion of B-splines and point masses.
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3.
  • Nedic, Mitja, et al. (författare)
  • Herglotz functions and applications in electromagnetics
  • 2020
  • Ingår i: Advances in Mathematical Methods for Electromagnetics. - : Institution of Engineering and Technology. - 9781785613845 - 9781785613852 ; , s. 491-514
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • Herglotz functions inevitably appear in pure mathematics, mathematical physics, and engineering with a wide range of applications. In particular, they are the pertinent functions to model passive systems, and thus appear in modeling of electromagnetic phenomena in circuits, antennas, materials, and scattering. In this chapter, we review the basic theory of Herglotz functions and its applications to determine sum rules and physical bounds for passive systems.
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5.
  • Nordebo, Sven, et al. (författare)
  • Passive approximation and optimization
  • 2015
  • Ingår i: Progress in Electromagnetics Research Symposium (PIERS). - 9781934142295 ; , s. 84-
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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6.
  • Dalarsson, Mariana, et al. (författare)
  • Wave propagation in waveguides with graded plasmonic obstacles
  • 2021
  • Ingår i: Journal of the Optical Society of America. B, Optical physics. - : OPTICAL SOC AMER. - 0740-3224 .- 1520-8540. ; 38:1, s. 104-113
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, wave propagation in a hollow waveguide with a graded dielectric layer is studied. Analytic formulas are derived for the electric field components as well as general analytical results for the reflection and transmission coefficients for propagating waves. These results are all valid for waveguides of arbitrary cross sections, and the derived reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a wry thin homogeneous dielectric layer using cascading and mode-matching techniques. Furthermore, the power transmission, reflection, and absorption coefficients, as functions of frequency and layer width, are studied, showing the expected behavior of these parameters. The method proposed in this paper gives directly applicable results that do not require cascading and mode matching, while at the same time having the ability to model smooth transitions that are more realistic in several applications. (C) 2020 Optical Society of America
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7.
  • Nordebo, Sven, et al. (författare)
  • Fisher information analysis and preconditioning in electrical impedance tomography
  • 2010
  • Ingår i: Journal of Physics: Conference Series 224 (2010), 1742-6588. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; , s. 012057-
  • Konferensbidrag (refereegranskat)abstract
    • An adjoint field approach is used to formulate a general numerical framework for Fisher information based sensitivity analysis in electrical impedance tomography. General expressions are given for the gradients used in standard least squares optimization, i.e., the Jacobian related to the forward problem, and it is shown that these gradient expressions are consistent with commonly used electrode models such as the shunt model and the complete electrode model. By using the adjoint field formulations together with a variational analysis, it is also shown how the computation of the Fisher information can be integrated with the gradient calculations used for optimization. It is furthermore described how the Fisher information analysis and the related sensitivity map can be used in a preconditioning strategy to obtain a well balanced parameter sensitivity and improved performance for gradient based quasi-Newton optimization algorithms in electrical impedance tomography. Numerical simulations as well as reconstructions based on experimental data are used to illustrate the sensitivity analysis and the performance of the improved inversion algorithm in a four-electrode measurement set-up.
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10.
  • Nordebo, Sven, et al. (författare)
  • Cylindrical multipole expansion for periodic sources with applications for three-phase power cables
  • 2018
  • Ingår i: Mathematical methods in the applied sciences. - : Wiley-Blackwell. - 0170-4214 .- 1099-1476. ; 41:3, s. 959-965
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a c ylindrical multipole expansion for periodic sources with applications for three-phase power cables.It is the aim of the contribution to provide some analytical solutions and techniques that can be useful in the calculation ofcable losses. Explicit analytical results are given for the fields generated by a three-phase helical current distribution andwhich can be computed efficiently as an input to other numerical methods such as, for example , the Method of Moments.It is shown that the field computations are numerically stable at low frequencies (such as 50 Hz) as well as in the quasi-magnetostatic limit provided that sources are divergence-free. The cylindrical multipole expansion is fur thermore usedto derive an efficient analytical model of a measurement coil to measure and estimate the complex valued permeability ofmagnetic steel armour in the presence of a strong skin-effect.
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