| 31. |
- Nordebo, Sven, et al.
(författare)
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Low-frequency dispersion characteristics of a multilayered coaxial cable
- 2013
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Ingår i: Journal of Engineering Mathematics. - : Springer Netherlands. - 0022-0833 .- 1573-2703. ; 83:1, s. 169-184
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides an exact asymptotic analysis regarding the low-frequency dispersion characteristics of a multilayered coaxial cable. A layer-recursive description of the dispersion function is derived that is well suited for asymptotic analysis. The recursion is based on two well-behaved (meromorphic) subdeterminants defined by a perfectly electrically conducting (PEC) and a perfectly magnetically conducting termination, respectively. For an open waveguide structure, the dispersion function is a combination of two such functions, and there is only one branch point that is related to the exterior domain. It is shown that if there is one isolating layer and a PEC outer shield, then the classical Weierstrass preparation theorem can be used to prove that the low-frequency behavior of the propagation constant is governed by the square root of the complex frequency, and an exact analytical expression for the dominating term of the asymptotic expansion is derived. It is furthermore shown that the same asymptotic expansion is valid to its lowest order even if the outer shield has finite conductivity and there is an infinite exterior region with finite nonzero conductivity. As a practical application of the theory, a high-voltage direct current (HVDC) power cable is analyzed and a numerical solution to the dispersion relation is validated by comparisons with the asymptotic analysis. The comparison reveals that the low-frequency dispersion characteristics of the power cable is very complicated and a first-order asymptotic approximation is valid only at extremely low frequencies (below 1 Hz). It is noted that the only way to come to this conclusion is to actually perform the asymptotic analysis. Hence, for practical modeling purposes, such as with fault localization, an accurate numerical solution to the dispersion relation is necessary and the asymptotic analysis is useful as a validation tool.
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| 32. |
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| 33. |
- Nordebo, Sven, et al.
(författare)
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On the Design of Optimal Measurements for Antenna Near-Field Imaging Problems
- 2006
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Ingår i: AIP Conference Proceedings. - : AIP. ; 834, s. 234-249
-
Konferensbidrag (refereegranskat)abstract
- A mathematical framework is introduced for optimization of antenna near-field imaging problems, based on the multipole expansion of the electromagnetic field, the Fisher information to quantify the quality of data and use of modern interior point convex optimization techniques. We consider the general problem of optimizing the measurement sensor allocation for parameter estimation in distributed systems, and in particular the problem of optimizing the measurement set-up for antenna near-field estimation. As an application example for antenna near-field imaging, we consider a relevant measurement set-up using cylindrical probing coordinates. The convex optimization problem is examined using duality theory, and it is shown that several structural properties of the optimal measurement problem can be exploited in developing an efficient interior point optimization method. In particular, we show that the cylindrical measurement set-up yields a Fisher information matrix with block diagonal structure, a feature which can be directly exploited in the optimization algorithm by reducing the number of dual decision variables.
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| 34. |
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| 35. |
- Nordebo, Sven, et al.
(författare)
-
On the relation between optimal wideband matching and scattering of spherical waves
- 2011
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 59:9, s. 3358-3369
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedUsing an exact circuit analogy for the scattering ofvector spherical waves, it is shown how the problem of determiningthe optimal scattering bounds for a homogeneous spherein its high-contrast limit is identical to the closely related, andyet very different problem of finding the broadband tuning limitsof the spherical waves. Using integral relations similar to Fano’sbroadband matching bounds, the optimal scattering limitationsare determined by the static response as well as the high-frequencyasymptotics of the reflection coefficient. The scattering view of thematching problem yields explicitly the necessary low-frequencyasymptotics of the reflection coefficient that is used with Fano’sbroadband matching bounds for spherical waves, something thatappears to be non-trivial to derive from the classical networkpoint of view.
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| 36. |
- Nordebo, Sven, et al.
(författare)
-
Optimal Realizations of Passive Structures
- 2014
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 62:9, s. 4686-4694
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a convex optimization approach to study optimal realizations of passive electromagnetic structures. The optimization approach complements recently developed theory and techniques to derive sum rules and physical limitations for passive systems operating over a given bandwidth. The sum rules are based solely on the analytical properties of the corresponding Herglotz functions. However, the application of sum rules is limited by certain assumptions regarding the low- and high-frequency asymptotic behavior of the system, and the sum rules typically do not give much information towards an optimal realization of the passive system at hand. In contrast, the corresponding convex optimization problem is formulated to explicitly generate a Herglotz function as an optimal realization of the passive structure. The procedure does not require any additional assumptions on the low- and high frequency asymptotic behavior, but additional convex constraints can straightforwardly be incorporated in the formulation. Typical application areas are concerned with antennas, periodic structures, material responses, scattering, absorption, reflection, and extinction. In this paper, we consider three concrete examples regarding dispersion compensation for waveguides, passive metamaterials and passive radar absorbers.
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| 37. |
- Nordebo, Sven, et al.
(författare)
-
Passive approximation and optimization
- 2015
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Ingår i: Progress in Electromagnetics Research Symposium (PIERS). - 9781934142295 ; , s. 84-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 38. |
- Nordebo, Sven, et al.
(författare)
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Statistical Signal Analysis for the Inverse Source Problem of Electromagnetics
- 2006
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X. ; 54:6, s. 2357-2361
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Tidskriftsartikel (refereegranskat)abstract
- A statistical signal analysis for the inverse source problem of electromagnetics is given. We consider the problem of estimating either the near field or the radiating current distribution from a measurement of the far field. The solution is derived via a linear operator formalism, and the ill-posedness of the reconstruction is quantified by using the Cramer-Rao lower bound which is explicitly given in terms of the multipole expansion of the electromagnetic field. A numerical study is included to illustrate the theoretical results.
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| 39. |
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| 40. |
- Nordebo, Sven, et al.
(författare)
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Wave modeling and fault localization for underwater power cables
- 2011
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Ingår i: 2011 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications (APWC). - : IEEE Press. - 9781457700460 ; , s. 698-701
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Konferensbidrag (refereegranskat)abstract
- This paper describes some preliminary results regarding Time-Domain pulse Reflection (TDR) measurements and modeling performed on the Baltic Cable submarine HVDC link between southern Sweden and northern Germany. The measurements were conducted in collaboration between the Linnaeus University, Lund University, Baltic Cable AB and ABB High Voltage Cables AB, and is part of the research project: “Fundamental wave modeling for signal estimation on lossy transmission lines”. Preliminary results on measurements and modeling are included here, as well as a first numerical study regarding the low-frequency dispersion characteristics of power cables. The numerical study shows that the finite conductivity of the cable lead shield has a great impact on the losses at low frequencies (0-1 kHz), and that the low-frequency asymptotics of the propagation constant is consistent with common propagation models based on the skin-effect.
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