| 61. |
- Dalarsson, Mariana, et al.
(författare)
-
Absorption and optimal plasmonic resonances for small ellipsoidal particles in lossy media
- 2017
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Ingår i: Journal of Physics D. - : Institute of Physics (IOP). - 0022-3727 .- 1361-6463. ; 50:34
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Tidskriftsartikel (refereegranskat)abstract
- A new simplified formula is derived for the absorption cross section of small dielectric ellipsoidal particles embedded in lossy media. The new expression leads directly to a closed form solution for the optimal conjugate match with respect to the surrounding medium, i.e. the optimal permittivity of the ellipsoidal particle that maximizes the absorption at any given frequency. This defines the optimal plasmonic resonance for the ellipsoid. The optimal conjugate match represents a metamaterial in the sense that the corresponding optimal permittivity function may have negative real part (inductive properties), and can not in general be implemented as a passive material over a given bandwidth. A necessary and sufficient condition is derived for the feasibility of tuning the Drude model to the optimal conjugate match at a single frequency, and it is found that all the prolate spheroids and some of the (not too flat) oblate spheroids can be tuned into optimal plasmonic resonance at any desired center frequency. Numerical examples are given to illustrate the analysis. Except for the general understanding of plasmonic resonances in lossy media, it is also anticipated that the new results can be useful for feasibility studies with e.g. the radiotherapeutic hyperthermia based methods to treat cancer based on electrophoretic heating in gold nanoparticle suspensions using microwave radiation.
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| 62. |
- Dalarsson, Mariana
(författare)
-
Online power transformer diagnostics using multiple modes of microwave radiation
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present thesis, we propose and investigate a new approach to diagnose the effects of the various degradation mechanisms, including thermal degradation at hot spots, winding deformations due to the mechanical forces from short circuit currents, partial discharges due to local electric field surges, and increased moisture levels in the cellulose insulation due to decomposition, that affect electric power transformers during their normal operation in an electric power grid.Although the proposed diagnostics method can in principle be used to detect various degradation mechanisms mentioned above, we focus in the present thesis on mechanical deformations of transformer winding structures. Such mechanical deformations are most often caused by mechanical forces from short circuit currents, but they may also be caused by initial manufacturing errors and inconsistencies not detected by the power transformers’ suppliers quality assurance processes.We model a transformer winding surrounded by the transformer-tank wall and the magnetic core as a two-dimensional parallel plate waveguide or as a three-dimensional coaxial waveguide, where one metallic boundary (plate or cylinder) represents the wall of the transformer tank and the other metallic boundary (plate or cylinder) represents the iron core that conducts the magnetic flux. In between there is a set of parallel or coaxial conductors representing the winding segments.The new principle proposed in the present thesis is to insert a number of antennas into a transformer tank to radiate and measure microwave fields interacting with metallic structures and insulation. The responses from the emitted microwave radiation are expected to be sensitive to material properties that reflect the changes caused by any harmful deterioration processes mentioned above. Specifically, we investigate the mechanical deformations of transformer winding structures by determining the locations of the individual winding segments or turns, using measurements of the scattered fields at both ends of the winding structure. We solve the propagation problem using conventional waveguide theory, including mode-matching and cascading techniques.The inverse problem is solved using modified steepest-descent optimization methods. The optimization model is tested by comparing our calculated scattering data with synthetic measurement data generated by the commercial program HFSS.A good agreement is obtained between the calculated and measured positions of winding segments for a number of studied cases, which indicates that the diagnostics method proposed in the present thesis couldbe potentially useful as a basis for the design of a future commercial on-line winding monitoring device. However, further development of the theoretical analysis of a number of typical winding deformations, improvements of the optimization algorithms and a practical study with measurements on an actual power transformer structure are all needed to make an attempt to design a commercial winding monitoring device feasible.
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| 63. |
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| 64. |
- Dalarsson, Mariana, et al.
(författare)
-
TE-wave propagation in a graded waveguide structure
- 2018
-
Ingår i: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials). - : IEEE. - 9781538647028 - 9781538647035 - 9781538647011 ; , s. 93-95
-
Konferensbidrag (refereegranskat)abstract
- We investigate TE-wave propagation in a hollow waveguide with a graded dielectric barrier, using an equivalent model of the waveguide filled with a stratified medium. General formulae for the electric field components of the TE-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. As an illustration, we obtain the exact analytical results for the electric field components in a rectangular waveguide, as well as the exact analytical results for reflection and transmission coefficients which are valid for waveguides of arbitrary cross sectional shapes.
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| 65. |
- Dalarsson, Mariana, et al.
(författare)
-
TE-wave propagation in a graded waveguide structure
- 2018
-
Ingår i: Proceedings 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- We investigate TE-wave propagation in a hollow waveguide with a graded dielectric barrier, using an equivalent model of the waveguide filled with a stratified medium. General formulae for the electric field components of the TE-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. As an illustration, we obtain the exact analytical results for the electric field components in a rectangular waveguide, as well as the exact analytical results for reflection and transmission coefficients which are valid for waveguides of arbitrary cross sectional shapes.
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| 66. |
- Dalarsson, Mariana, et al.
(författare)
-
TE-wave propagation in graded waveguide structures
- 2020
-
Ingår i: OSA Continuum. - : Optical Society of America. - 2578-7519. ; 3:1, s. 67-76
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate TE-wave propagation in a hollow waveguide with a graded dielectric layer, described using a hyperbolic tangent function. General formulae for the electric field components of the TE-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. We illustrate the exact analytical results for the electric field components in the special case of a rectangular waveguide. Furthermore, we derive exact analytical results for the reflection and transmission coefficients valid for waveguides of arbitrary cross sectional shapes. Finally, we show that the obtained reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a very thin homogeneous dielectric layer using mode-matching and cascading. The proposed method gives analytical results that are directly applicable without the need of mode-matching, and it has the ability to model realistic, smooth transitions. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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| 67. |
- Dalarsson, Mariana, et al.
(författare)
-
TE-wave propagation in graded waveguide structures
- 2020
-
Ingår i: OSA Continuum. - : Optica Publishing Group. - 2578-7519. ; 3:1, s. 67-67
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate TE-wave propagation in a hollow waveguide with a graded dielectric layer, described using a hyperbolic tangent function. General formulae for the electric field components of the TE-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. We illustrate the exact analytical results for the electric field components in the special case of a rectangular waveguide. Furthermore, we derive exact analytical results for the reflection and transmission coefficients valid for waveguides of arbitrary cross sectional shapes. Finally, we show that the obtained reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a very thin homogeneous dielectric layer using mode-matching and cascading. The proposed method gives analytical results that are directly applicable without the need of mode-matching, and it has the ability to model realistic, smooth transitions.
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| 68. |
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| 69. |
- Dalarsson, Mariana, et al.
(författare)
-
TM-wave propagation in a graded waveguide structure
- 2019
-
Ingår i: 2019 URSI International Symposium on Electromagnetic Theory (EMTS). - : IEEE. ; , s. 1-4
-
Konferensbidrag (refereegranskat)abstract
- We investigate TM-wave propagation in a hollow waveguide with a graded dielectric layer, described using a hyperbolic tangent function. General formulae for the electric field components of the TM-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. We derive the analytical results for the reflection and transmission coefficients valid for waveguides of arbitrary cross sectional shapes. Thereby, we show that the obtained reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a very thin homogeneous dielectric layer using mode-matching and cascading. The proposed method is tractable since it gives analytical results that are directly applicable without the need of mode-matching, and it has the ability to model realistic, smooth transitions.
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| 70. |
- Dalarsson, Mariana, et al.
(författare)
-
TM-wave propagation in a graded waveguide structure
- 2019
-
Ingår i: Proceedings 2019 URSI International Symposium on Electromagnetic Theory (EMTS). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- We investigate TM-wave propagation in a hollow waveguide with a graded dielectric layer, described using a hyperbolic tangent function. General formulae for the electric field components of the TM-waves, applicable to hollow waveguides with arbitrary cross sectional shapes, are presented. We derive the analytical results for the reflection and transmission coefficients valid for waveguides of arbitrary cross sectional shapes. Thereby, we show that the obtained reflection and transmission coefficients are in exact asymptotic agreement with those obtained for a very thin homogeneous dielectric layer using mode-matching and cascading. The proposed method is tractable since it gives analytical results that are directly applicable without the need of mode-matching, and it has the ability to model realistic, smooth transitions.
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