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  • 1.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Tassin, Philippe
    Analytical solution for wave propagation through a graded index interface between a right-handed and a left-handed material2009Ingår i: Optics Express, E-ISSN 1094-4087, Vol. 17, nr 8, s. 6747-6752Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have investigated the transmission and reflection properties of structures incorporating left-handed materials with graded index of refraction. We present an exact analytical solution to Helmholtz' equation for a graded index profile changing according to a hyperbolic tangent function along the propagation direction. We derive expressions for the field intensity along the graded index structure, and we show excellent agreement between the analytical solution and the corresponding results obtained by accurate numerical simulations. Our model straightforwardly allows for arbitrary spectral dispersion.

  • 2.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Tassin, Philippe
    Jaksic, Zoran
    Exact analytical solution for oblique incidence on a graded index interface between a right-handed and a left-handed material2009Ingår i: Journal of Optoelectronics and Biomedical Materials, ISSN 2066-0049, Vol. 1, nr 4, s. 345-352Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have determined the scattering parameters of optical structures incorporating both left-handed metamaterials (LHM) and conventional ("right-handed") materials (RHM) for the case when the refractive index at the LHM-RHM interface is graded, for oblique incidence at an arbitrary angle and for arbitrary spectral dispersion. We derived an accurate analytical solution to Helmholtz’ equation for the case of the refractive index gradient varying as a hyperbolic tangent where the steepness of the index transition may be arbitrary, even of the order of vacuum wavelength. We determined the expressions for the field intensity along the LHM-RHM structure with refractive index gradient. We show that there is an excellent agreement between our analytical results and the accurate numerical simulations done by finite element method.

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  • 3. Tassin, P.
    et al.
    Dalarsson, Nils
    KTH.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jakšić, Z.
    Exact analytical treatment of the graded interfaces between positive and negative refractive index media2009Ingår i: 9th International Conference on Telecommunications in Modern Satellite, Cable, and Broadcasting Services, TELSIKS 2009 - Proceedings of Paper, IEEE , 2009, s. 143-146Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigated electrodynamics of structures incorporating composites with negative dielectric permittivity and magnetic permeability, the popular "left-handed metamaterials". We obtained the exact analytical solutions to the Helmholtz equation for gradient-index interfaces between the positive and negative index part in the special case of matched impedances of the two materials. We derived expressions for the field intensity and compared the analytical results with the corresponding results obtained by the numerical simulations using the Finite Element Method (FEM). The model allows for arbitrary spectral dispersion and lossy media.

  • 4.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jaksic, Zoran
    IHTM Institute of Microelectronic Technologies and Single Crystals, Belgrade, Serbia.
    Tassin, Philippe
    Vrije Universiteit Brussel, Brussels, Belgium.
    Structures Containing Left-Handed Metamaterials with Refractive Index Gradient: Exact Analytical Versus Numerical Treatment2009Ingår i: Microwave Review, ISSN 1450-5835, ISSN 1450-5835, Vol. 15, nr 2, s. 2-5Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigated propagation of electromagnetic waves through composite structures with negative refractive index, the popular ”left-handed metamaterials”, for the case when there is a gradient of refractive index. We obtained the exact analytical solutions to the Helmholtz equation valid for arbitrary steepness of the graded interface between the positive and the negative index part. We analyzed the special case of matched impedances of the two constituent materials within the metamaterial composite. We derived analytical expressions for the field intensity, transmission and reflection coefficients and compared them with the results obtained by the numerical simulations using the Finite Element Method. The model allows for arbitrary spectral dispersion and lossy media.

    Ladda ner fulltext (pdf)
    fulltext
  • 5.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dalarsson, Nils
    KTH.
    Jaksic, Z.
    Analytical approach to lossy wave propagation through a graded interface containing negative index material2011Ingår i: Int. Conf. Telecommun. Mod. Satell., Cable Broadcast. Serv., TELSIKS - Proc. Pap., 2011, s. 39-42Konferensbidrag (Refereegranskat)
    Abstract [en]

    The transmission and reflection properties of lossy structures involving left-handed materials with graded permittivity and permeability have been investigated. We present an exact analytical solution to Helmholtz' equation for a lossy case with the graded real parts of permittivity and permeability profile changing according to a hyperbolic tangent function along the direction of propagation. The simple analytical solutions and graphical results for the field intensity along the graded structure are presented. The model straightforwardly allows for arbitrary temporal dispersion.

  • 6. Dalarsson, Nils
    et al.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Golubovic, Leonardo
    Introductory Statistical Thermodynamics2011Bok (Övrigt vetenskapligt)
    Abstract [en]

    Elementary Statistical Thermodynamics is a text for an introductory one-semester course in statistical thermodynamics for upper-level undergraduate and graduate students in physics and engineering. The book offers a high level of detail in derivations of all equations and results. This information is necessary for students to grasp difficult concepts in physics that are needed to move on to higher level courses. The text is elementary, self contained, and mathematically well-founded, containing a number of problems with detailed solutions to help students to grasp the more difficult theoretical concepts. Beginning chapters place an emphasis on quantum mechanics Includes problems with detailed solutions and a number of detailed theoretical derivations at the end of each chapter Provides a high level of detail in derivations of all equations and results.

  • 7.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jaksic, Zoran
    Lossy gradient index metamaterial with sinusoidal periodicity of refractive index: case of constant impedance throughout the structure2011Ingår i: J NANOPHOTONICS, ISSN 1934-2608, Vol. 5, s. 051804-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We used an exact analytical approach to investigate the electromagnetic wave propagation across an isotropic metamaterial composite with i. a sinusoidally periodic gradient of the real parts of the effective permittivity and permeability, ii. spatially uniform imaginary parts of the effective permittivity and permeability, and iii. spatially uniform impedance. The real part of the effective refractive index can be positive and negative along the direction of nonhomogeneity. A remarkably simple direct solution for the field distribution was obtained.

  • 8.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Asenov, T.
    Doncov, N.
    Gradient index metamaterial with arbitrary loss factors in RHM and LHM media: The case of constant impedance throughout the structure2012Ingår i: PIERS 2012 Moscow: Progress In Electromagnetics Research Symposium, Electromagnetics Academy , 2012, s. 1390-1394Konferensbidrag (Refereegranskat)
    Abstract [en]

    The transmission and reflection properties of lossy structures involving left-handed materials with graded permittivity and permeability have been investigated. We present an exact analytical solution to Helmholtz' equation for a lossy case with the graded both real and imaginary parts of permittivity and permeability profile changing according to a hyperbolic tangent function along the direction of propagation. This allows for different loss factors in the two media. The expressions and graphical results for the field intensity along the graded structure are presented. The analytical solution is validated by a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms, where a close agreement between the analytic and numerical results is obtained.

  • 9.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jaksic, Z.
    Lossy gradient index metamaterial with general periodic permeability and permittivity: The case of constant impedance throughout the structure2012Ingår i: Proceedings Of Progress In Electromagnetics Research Symposium (PIERS 2012), Electromagnetics Academy , 2012, s. 190-194Konferensbidrag (Refereegranskat)
    Abstract [en]

    We utilize an exact analytical approach to investigate the electromagnetic wave propagation across an infinite metamaterial composite with general periodic gradient effective permittivity and permeability. A general analytic solution for the field distribution is obtained for an arbitrary periodic variation of complex refractive index across the structure. The calculation is done for the case of constant impedance across the structure. Arbitrary temporal dispersion and losses are allowed and the model is generally applicable to inhomogeneous and anisotropic media simultaneously containing positive and negative refractive index constituents as long as the effective medium approximation is valid.

  • 10.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Doncov, N.
    Univ Nis, Nish, Serbia.
    Jaksic, Z.
    Univ Belgrade, Belgrade, Serbia.
    Lossy gradient index transmission optics with arbitrary periodic permittivity and permeability and constant impedance throughout the structure2012Ingår i: Journal of Optics, ISSN 2040-8978, E-ISSN 2040-8986, Vol. 14, nr 6, s. 065102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A remarkably simple exact analytical solution is obtained for the electromagnetic field distribution across infinite metamaterial-containing composites with any arbitrary periodic variation of complex effective permittivity and permeability for the case of constant impedance across the structure. Arbitrary temporal dispersion and losses are allowed and the model is generally applicable to different inhomogeneous and anisotropic media simultaneously containing positive and negative refractive index constituents, as long as the effective medium approximation remains valid. The analytical solution is validated by a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms, where a close agreement between the analytic and numerical results is obtained.

  • 11.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Motevasselian, Alireza
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    On using multiple modes to reconstruct conductor locations in a power transformer winding2012Ingår i: Progress in Electromagnetics Research Symposium (PIERS 2012), Electromagnetics Academy , 2012, s. 516-523Konferensbidrag (Refereegranskat)
    Abstract [en]

    An initial study of a novel method to diagnose the effects of the various degradation mechanisms on the power transformers, while in operation, is presented. We model a transformer winding surrounded by the transformer-tank wall and the magnetic core as a two-dimensional parallel plate waveguide, where one plate represents the wall of the transformer tank and the other plate represents the iron core that conducts the magnetic flux. In between there is a set of parallel conductors representing the winding segments. The new principle is to insert antennas inside the transformer tank to radiate and measure microwave fields that interact with the metallic structure and the insulation. The responses from the radiated waves are assumed to be sensitive to material properties that reflect any harmful deterioration processes. In particular, we study the mechanical deformations of the transformer winding by determining the locations of the individual conductors, from measurements of the scattered fields at both ends. The propagation problem is solved accurately and efficiently by conventional waveguide theory, including mode- matching and cascading techniques. We employ optimization as a suitable method to solve the inverse problem and obtain a good agreement between the calculated and measured positions of winding segments.

  • 12.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Asenov, Tatjana
    Doncov, Nebojsa
    Arbitrary Loss Factors In The Wave Propagation Between RHM And LHM Media With Constant Impedance Throughout The Structure2013Ingår i: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 137, s. 527-538Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the wave propagation properties in lossy structures with graded permittivity and permeability involving left-handed metamaterials. An exact analytic solution to Helmholtz' equation for a lossy case with both real and imaginary parts of permittivity and permeability profile, changing according to a hyperbolic tangent function along the direction of propagation, is obtained. It allows for different loss factors in RHM and LHM media. Thereafter, the corresponding numerical solution for the field intensity along the composite structure is obtained by means of a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms. We present the expressions and graphical results for the field intensity along the composite structure and compare the analytic and numerical solutions, showing that there is an excellent agreement between them.

  • 13.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Conductor Locations Reconstruction in a Cylindrical Winding Model2013Ingår i: Proceedings of PIERS 2013 in Stockholm, Sweden, August 12-15, 2013, ELECTROMAGNETICS ACAD , 2013, s. 850-857Konferensbidrag (Refereegranskat)
    Abstract [en]

    A study of a novel method to detect mechanical deformations of windings in a power transformer, while in operation, is presented. We employ an approximate model of a transformer winding surrounded by the transformer-tank wall and the magnetic core. The transformer winding is viewed as a structure consisting of thin conducting cylindrical rings (winding segments or turns) situated within a coaxial cylindrical waveguide, where the inner conducting cylinder represents the iron core that conducts the magnetic flux and the outer conducting cylinder represents the wall of the transformer tank. The idea is to insert antennas inside the transformer tank above and below the winding to radiate and measure microwave fields that interact with the metallic structure and the insulation. The responses from the radiated waves are assumed to be sensitive to any mechanical deformations that could be caused by electromagnetic forces due to short-circuit currents and possible manufacturing weaknesses. The goal is to determine the radial locations of the individual winding segments or individual turns from measurements of the scattered fields at both ends. The propagation problem is solved by conventional waveguide theory, including mode-matching and cascading techniques. We utilize optimization as a suitable method to solve the inverse problem and obtain an agreement between the reconstructed and true positions of the winding segments.

  • 14.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Asenov, Tatjana
    Doncov, Nebojsa
    Jaksic, Zoran
    Exact analytical solution for fields in gradient index metamaterials with different loss factors in negative and positive refractive index segments2013Ingår i: Journal of Nanophotonics, ISSN 1934-2608, Vol. 7, s. 073086-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Gradient refractive index metamaterials are of interest for various applications of transformation optics. Wave propagation through gradient index metamaterials using an exact analytical approach is investigated. Composite materials containing constituents with negative real and positive real indexes of refraction are considered. An exact analytical solution for the field distribution is obtained for the sinusoidal spatial variation of complex effective permittivity and permeability along a fixed direction, under the assumption that the wave impedance remains spatially uniform across the structure. Loss factors in the constituent materials can be different from each other corresponding to the realistic situations. Temporal dispersion can be arbitrary subject to the physical limitations imposed by the Kramers-Kronig relations. A numerical model based on the Z-transform is developed to verify the analytical results. The approach can be applied to arbitrary periodic refractive index profiles using the Fourier series method.

  • 15.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    First-order perturbation approach to elliptic winding deformations2013Ingår i: 2013 International Symposium on Electromagnetic Theory, EMTS 2013 - Proceedings, IEEE , 2013, s. 13-16Konferensbidrag (Refereegranskat)
    Abstract [en]

    We apply a novel on-line method to detect elliptic deformations of winding turns in a power transformer. We employ the first-order perturbation theory to a transformer winding surrounded by the transformer tank wall and the magnetic core. The transformer winding is modeled as a structure consisting of thin conducting cylindrical rings (winding segments or turns) situated within a coaxial cylindrical waveguide, where the inner conducting cylinder represents the magnetic core and the outer conducting cylinder represents the wall of the transformer tank. We simulate antennas inside the transformer tank to radiate and measure microwave fields, in order to identify and quantify elliptic deformations of the individual winding segments or individual turns. The propagation problem is solved by conventional waveguide theory, including mode-matching and cascading techniques. We utilize optimization to solve the inverse problem and obtain a good agreement between the reconstructed and true deformations of the winding segments.

  • 16.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    First-order perturbation approach to transformer winding deformations2013Ingår i: Progress In Electromagnetics Research Letters, ISSN 1937-6480, Vol. 43, s. 1-14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An on-line method to detect radial mechanical deformations of power transformer winding turns is presented. First-order perturbation theory is applied to a transformer winding surrounded by the transformer tank wall and the iron core. The transformer wind- ing is modeled as thin conducting cylindrical rings (winding segments or turns) situated within a coaxial waveguide, where the outer con- ducting cylinder represents the transformer tank wall while the inner conducting cylinder represents the iron core. Antennas which radi- ate and measure microwave fields are proposed inside the transformer tank in order to identify and quantify the mechanical deformations of winding turns. The direct propagation problem is solved using conventional waveguide theory with mode-matching and cascading techniques. An optimization algorithm is then used to solve the inverse problem whereby a good agreement between the reconstructed and true deformations of the winding segments is obtained.

  • 17. Jaksic, Z.
    et al.
    Sarajlic, M.
    Lazic, Z.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dalarsson, Nils
    KTH.
    Randjelovic, D.
    Radulovic, K.
    Tanaskovic, D.
    Gradient-index infrared metamaterials based on metal-dielectric submicrometer pillar arrays2013Ingår i: 2013 11th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Services, TELSIKS 2013, IEEE , 2013, s. 21-24Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the design and microfabrication of a two-dimensional metal-dielectric metamaterial structure based on an array of pillars with submicrometer diameters and heights. The diameters of pillars periodically vary along one axis in a sawtooth fashion and are constant along the other. The electromagnetic field distribution within this graded metamaterial was considered utilizing an accurate analytical approach. The pillar arrays were fabricated in photoresist and subsequently covered with a sputter-deposited aluminum film. Structures were defined by direct laser writing in photoresist film. Controlled overexposure has been applied in order to make pillar features smaller than the nominal resolution of the equipment. The structures were characterized by optical and atomic force microscopy and by angle-dependent Fourier Transform infrared spectroscopy. The produced graded frequency-selective surfaces may be used e.g. in sensing.

  • 18.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Asenov, T.
    Doncov, N.
    Lossy transmision with arbitrary gradient permittivity and permeability and constant impedance throughout the structure2013Ingår i: 2013 11th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Services, TELSIKS 2013, IEEE , 2013, s. 25-28Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a remarkably simple exact analytical solution for the electromagnetic field distribution across an infinite metamaterial composite with an arbitrary graded variation of complex effective permittivity and permeability for the case of constant impedance across the structure. Arbitrary temporal dispersion and losses are allowed and the model is generally applicable to different inhomogeneous and anisotropic media simultaneously containing positive and negative refractive index constituents, as long as the effective medium approximation remains valid. The analytical solution is validated by a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms, where a close agreement between the analytic and numerical results is obtained.

  • 19.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Online power transformer diagnostics using multiple modes of microwave radiation2013Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    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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  • 20.
    Norgren, Martin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Motevasselian, Alireza
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Reconstruction of boundary perturbations in a waveguide2013Ingår i: 2013 International Symposium on Electromagnetic Theory, EMTS 2013 - Proceedings, IEEE , 2013, s. 934-937Konferensbidrag (Refereegranskat)
    Abstract [en]

    The inverse problem of reconstructing boundary deformations in a parallel plate waveguide is solved by using a first order perturbation method applied to the dominant TEM-mode. Regularization using the L-curve criterion is applied and investigated. Reconstruction results from using reflection data are presented and influences from higher order propagating and trapped modes are demonstrated.

  • 21. Jakšić, Z.
    et al.
    Sarajlić, M.
    Lazić, Ž.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Randjelović, D.
    Radulović, K.
    Tanasković, D.
    Two-dimensional gradient-index metamaterial with sawtooth profile2013Ingår i: Microwave Review, ISSN 1450-5835, Vol. 19, nr 2, s. 96-101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate theoretically and experimentally a binary metal-dielectric metamaterial with a sawtooth profile. The structure consists of a two-dimensional array of pillars with submicrometer diameters. The pillar diameters linearly vary along one axis and are constant along the other. This furnishes a serrated spatial profile of effective refractive index along a single axis. We first present a set of analytical solutions defining the electromagnetic fields in such a structure. Further we give the results of our experimental fabrication of gradient metamaterial with a sawtooth spatial profile. The basic material for pillars was photoresist. Their geometry was defined using direct laser writing. Resist was overexposed in controlled manner in order to obtain pillars with diameters below the nominal resolution of the laser writer. The microfabricated pillars were coated by a sputter-deposited aluminum film. For characterization we utilized optical and atomic force microscopy and angledependent Fourier Transform infrared spectroscopy. We envision the applicability of our graded metasurfaces in transformation optics.

  • 22.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Motevasselian, Alireza
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Using multiple modes to reconstruct conductor locations in a cylindrical model of a power transformer winding2013Ingår i: International journal of applied electromagnetics and mechanics, ISSN 1383-5416, E-ISSN 1875-8800, Vol. 41, nr 3, s. 279-291Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A study of a novel method to detect mechanical deformations of windings in a power transformer, while in operation, is presented. We employ an approximate model of a transformer winding surrounded by the transformer-tank wall and the magnetic core. The transformer winding is viewed as a structure consisting of thin conducting cylindrical rings (winding segments or turns) situated within a coaxial cylindrical waveguide, where the inner conducting cylinder represents the iron core that conducts the magnetic flux and the outer conducting cylinder represents the wall of the transformer tank. The basic principle is to insert antennas inside the transformer tank above and below the winding to radiate and measure microwave fields that interact with the metallic structure and the insulation. The responses from the radiated waves are assumed to be sensitive to any mechanical deformations that could be caused by electromagnetic forces due to short-circuit currents and possible manufacturing weaknesses. The goal is to be able to determine the radial locations of the individual winding segments or individual turns from measurements of the scattered fields at both ends. The propagation problem is solved by conventional waveguide theory, including mode-matching and cascading techniques. We utilize optimization as a suitable method to solve the inverse problem and obtain a good agreement between the reconstructed and true positions of the winding segments.

  • 23.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Motevasselian, Alireza
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Online power transformer diagnostics using multiple modes of microwave radiation to reconstruct winding conductor locations2014Ingår i: Inverse Problems in Science and Engineering, ISSN 1741-5977, E-ISSN 1741-5985, Vol. 22, nr 1, s. 84-95Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel approach to diagnostics of transformer winding deformations, caused by mechanical forces from short-circuit currents, is presented. We employ a simple model of a transformer as a two-dimensional parallel plate waveguide. The upper plate represents the transformer tank wall and the lower plate represents the iron core which carries the magnetic flux. Between the two plates, we model the transformer winding by a set of parallel conductors. We utilize commercial simulation software to simulate the generation and measurement of microwave radiation at both ends of the winding structure. The radiation interacts with the metallic structures in the model waveguide. The measured responses from the model waveguide are expected to be sensitive to mechanical deformations of the transformer winding. We use conventional waveguide theory to solve the direct propagation problem, and an optimization method to solve the inverse problem. In particular, we determine the locations of winding segments, and obtain a good agreement between reconstructed and true conductor positions.

  • 24.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Emadi, S. M. H.
    Norgren, M
    Reconstruction of continuous deformations in a coaxial cylindrical waveguide using Tikhonov regularization2014Ingår i: 2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014, IEEE Press, 2014, s. 1-4Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a solution of the inverse problem of reconstructing boundary deformations in a coaxial cylindrical waveguide by using a first order perturbation method applied to the dominant TEM-mode. We have applied and investigated different orders of Tikhonov regularization using the L-curve criterion. The reconstruction results from using reflection data are presented and they indicate an agreement between the reconstructed and true continuous functions that describe the deformations of the waveguide boundaries. 

  • 25.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Mittra, Raj
    Exact analytical approach to a class of continuously graded flat lenses2015Ingår i: 2015 IEEE Radio and Antenna Days of the Indian Ocean, RADIO 2015, IEEE , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present exact analytical solutions for the electric and magnetic fields in continuously graded models of flat lenses. We model the lenses as compact composites with continuously varying permittivity and permeability functions, which asymptotically approach unity at the boundaries of the composite cylinder. We illustrate the application of the proposed procedure by obtaining exact analytical solutions for the electric and magnetic fields for a class of composite designs with constant permeability (μ = μ0) and radially graded permittivity.

  • 26.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    Jaksic, Zoran
    Exact Analytical Solution for Fields in a Lossy Cylindrical Structure with Linear Gradient Index Metamaterials2015Ingår i: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 151, s. 109-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the electromagnetic wave propagation across a finite inhomogeneous and anisotropic cylindrical metamaterial composite containing both positive and negative effective refractive index parts with linear spatial gradient. Exact analytical solutions for the electric and magnetic field distributions are obtained for a linear variation of effective refractive index across the structure. The exact analytical results for the electric and magnetic fields are compared to the numerical results obtained using the numerical simulation software HFSS. The model allows for general temporal dispersion and uniform losses within the composite.

  • 27.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Inverse scattering of two-dimensional boundary deformations in waveguide structures2015Ingår i: 2015 IEEE Radio and Antenna Days of the Indian Ocean, RADIO 2015, IEEE , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the principles for an on-line microwave-based monitoring system for power grid components. Such systems would be able to provide diagnostic information about the component in real time. The microwave propagation in complex waveguide structures, here representing the interior of the power grid components, is studied with the aim to detect and quantify shape or material changes with sufficient accuracy. Electromagnetic field analysis in conjunction with inverse problem theory is used to reconstruct the material and shape parameters. In this paper, we present preliminary results for reconstructions of two-dimensional localized deformations of a waveguide boundary, representing the inner structure of a power grid component.

  • 28.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Emadi, Seyed Mohamad Hadi
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Perturbation Approach to Reconstructing Deformations in a Coaxial Cylindrical Waveguide2015Ingår i: Mathematical problems in engineering (Print), ISSN 1024-123X, E-ISSN 1563-5147, artikel-id 915497Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study a detection method for continuous mechanical deformations of coaxial cylindrical waveguide boundaries, using perturbation theory. The inner boundary of the waveguide is described as a continuous PEC structure with deformations modeled by suitable continuous functions. In the present approach, the computation complexity is significantly reduced compared to discrete conductor models studied in our previous work. If the mechanically deformed metallic structure is irradiated by the microwave fields of appropriate frequencies, then, by means of measurements of the scattered fields at both ends, we can reconstruct the continuous deformation function. We apply the first-order perturbation method to the inverse problem of reconstruction of boundary deformations, using the dominant TEM-mode of the microwave radiation. Different orders of Tikhonov regularization, using the L-curve criterion, are investigated. Using reflection data, we obtain reconstruction results that indicate an agreement between the reconstructed and true continuous deformations of waveguide boundaries.

  • 29.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Boundary shape reconstructions in a coaxial waveguide using Bessel functions2016Ingår i: 2016 URSI INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC THEORY (EMTS), IEEE, 2016, s. 826-829Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates boundary shape reconstructions in coaxial waveguides using microwave scattering. Electromagnetic field perturbation theory together with inverse problem theory is used to reconstruct two-dimensional small boundary deformations on the inner boundary of a coaxial waveguide. Due to the first-order perturbation theory employed, the scattering parameters of the waveguide have linear dependencies on the continuous deformation function. Thus, the corresponding inverse problem can be linearized, and direct inversion can be employed to obtain the shape parameters. Tikhonov regularization is used to regularize the resulting ill-conditioned linear system. Finally, reconstruction results are presented for a few examples of two-dimensional localized shape deformations of coaxial waveguide boundaries, being in agreement with the actual shapes.

  • 30.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jaksic, Zoran
    Exact analytical solution for fields in a lossy cylindrical structure with hyperbolic tangent gradient index metamaterials2016Ingår i: Optical and quantum electronics, ISSN 0306-8919, E-ISSN 1572-817X, Vol. 48, nr 3, artikel-id 209Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The advent of metamaterials with tailorable frequency dispersion ensured the emergence of transformation optics with proposed applications that include cloaking devices, superconcentrators, superabsorbers, beam shapers and benders, field and polarization rotators, etc. A crucial property of interest for transformation optics is the possibility to custom design the spatial dependence of optical properties, i.e. to attain a gradient of effective refractive index. The cylindrical geometry has been one of the prototypal proposed forms and actually the first theoretical and experimental cloaking devices had radial symmetry. In this contribution we present an exact analytical approach to the solution of Helmholtz' equations applied to radial propagation of electromagnetic waves through a cylinder containing negative and positive refractive index parts. A hyperbolic tangent gradient of refractive index is assumed. Our approach is inspired by the correspondence between transformation optics and quantum mechanics. A remarkably simple exact analytical solution is derived that takes into account realistic losses in negative-positive refractive index material composites.

  • 31.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Perturbation approach to reconstructions of boundary deformations in waveguide structures2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis we develop inverse scattering algorithms towards the ultimate goal of online diagnostic methods. The aim is to detect structural changes inside power transformers and other major power grid components, like generators, shunt reactors etc. Power grid components, such as large power transformers, are not readily available from the manufacturers as standard designs. They are generally optimized for specific functions at a specific position in the power grid. Their replacement is very costly and takes a long time.

    Online methods for the diagnostics of adverse changes of the mechanical structure and the integrity of the dielectric insulation in power transformers and other power grid components, are therefore essential for the continuous operation of a power grid. Efficient online diagnostic methods can provide a real-time monitoring of mechanical structures and dielectric insulation in the active parts of power grid components. Microwave scattering is a candidate that may detect these early adverse changes of the mechanical structure or the dielectric insulation. Upon early detection, proper actions to avoid failure or, if necessary, to prepare for the timely replacement of the damaged component can be taken. The existing diagnostic methods lack the ability to provide online reliable information about adverse changes inside the active parts. More details about the existing diagnostic methods, both online and offline, and their limitations can be found in the licentiate thesis preceding the present PhD thesis.

    We use microwave scattering together with the inverse scattering algorithms, developed in the present work, to reconstruct the shapes of adverse mechanical structure changes. We model the propagation environment as a waveguide, in which measurement data can be obtained only at two ends (ports). Since we want to detect the onset of some deformation, that only slightly alters the scattering situation (weak scattering), we have linearized the inverse problem with good results. We have calculated the scattering parameters of the waveguide in the first-order perturbation, where they have linear dependencies on the continuous deformation function. A linearized inverse problem with a weak scattering assumption typically results in an ill-conditioned linear equation system. This is handled using Tikhonov regularization, with the L-curve method for tuning regularization parameters.

    We show that localized one-dimensional and two-dimensional shape deformations, for rectangular and coaxial waveguide models, are efficiently reconstructed using the inverse scattering algorithms developed from the first principles, i.e. Maxwell’s theory of electromagnetism. An excellent agreement is obtained between the reconstructed and actual deformation shapes for a number of studied cases. These results show that it is possible to use the inverse algorithms, developed in the present thesis, as a theoretical basis for the design of a future diagnostic device. As a part of the future work, it remains to experimentally verify the results obtained so far, as well as to further study the theoretical limitations posed by linearization (first-order perturbation theory) and by the assumption of the continuity of the metallic waveguide boundaries and their deformations.

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    Thesis
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    Errata
  • 32.
    Norgren, Martin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Ghasemifard, Fatemeh
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Scattering of lower order modes in a parallel plate waveguide loaded with a slightly deformed layer of conducting strips2016Ingår i: 2016 URSI INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC THEORY (EMTS), IEEE, 2016, s. 349-352Konferensbidrag (Refereegranskat)
    Abstract [en]

    The lower order modes are derived for a parallel plate waveguide loaded with a sheet of parallel conducting strips. Using a first order perturbation method, we derive the scattering parameters due to a small deformation of the sheet. Results for scattering within and between the novel slow mode and the ubiquitous TEM-mode are presented. With increasing angle between the strips and the direction of propagation, the interaction between the slow mode and the deformation shifts downwards in frequency, due to the reduced phase velocity.

  • 33.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Two-dimensional boundary shape reconstructions in rectangular and coaxial waveguides2016Ingår i: Wave motion, ISSN 0165-2125, E-ISSN 1878-433X, Vol. 66, s. 10-20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a method for shape reconstruction of deformed metallic boundaries in rectangular and coaxial waveguides using microwave scattering. Our developed reconstruction method is a theoretical basis for a future on-line microwave-based monitoring system for power grid components. The bundle of winding conductors in the active part of a typical power grid component is modeled as a continuous metallic surface. Then, electromagnetic field perturbation theory in conjunction with inverse problem theory is used to reconstruct the shape parameters of this surface. We assume small perturbations of the boundaries, such that the scattering parameters of the waveguide in the first-order perturbation have linear dependencies of the continuous deformation function. Thus, the corresponding inverse problem can be linearized and we can employ direct inversion, without the need for optimization which requires a higher computational effort. Tikhonov regularization is used to regularize the arising ill-conditioned linear system. The reconstructions, performed with noisy synthetic measurement data, show a good agreement with the actual shapes of the studied two-dimensional localized shape deformations for both rectangular and coaxial waveguide boundaries.

  • 34.
    Dalarsson, Mariana
    et al.
    Linnaeus Univ, Dept Phys & Elect Engn, S-35195 Växjö, Sweden.
    Nordebo, Sven
    Linnaeus Univ, Dept Phys & Elect Engn, S-35195 Växjö, Sweden.
    Sjöberg, Daniel
    Lund Univ, Dept Elect & Informat Technol, Box 118, S-22100 Lund, Sweden.
    Bayford, Richard
    Middlesex Univ, Dept Nat Sci, Hendon Campus, London NW4 4BT, England.
    Absorption and optimal plasmonic resonances for small ellipsoidal particles in lossy media2017Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, nr 34, artikel-id 345401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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,   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   the radiotherapeutic hyperthermia based methods to treat cancer based on electrophoretic heating in gold nanoparticle suspensions using microwave radiation.

  • 35.
    Dalarsson, Mariana
    et al.
    Linnaeus University, Department of Physics and Electrical Engineering, Växjö, Sweden.
    Mittra, Raj
    The Pennsylvania State University, Department of Electrical Engineering, EMC Laboratory, University Park, USA.
    Exact analytical solutions of continuously graded models of flat lenses based on transformation optics2017Ingår i: Facta Universitatis Series: Electronics and Energetics, ISSN 0353-3670, E-ISSN 2217-5997, Vol. 30, nr 4, s. 639-646Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a study of exact analytic solutions for electric and magnetic fields in continuously graded flat lenses designed utilizing transformation optics. The lenses typically consist of a number of layers of graded index dielectrics in both the radial and longitudinal directions, where the central layer in the longitudinal direction primarily contributes to a bulk of the phase transformation, while other layers act as matching layers and reduce the reflections at the interfaces of the middle layer. Such lenses can be modeled as compact composites with continuous permittivity (and if needed) permeability functions which asymptotically approach unity at the boundaries of the composite cylinder. We illustrate the proposed procedures by obtaining the exact analytic solutions for the electric and magnetic fields for one simple special class of composite designs with radially graded parameters. To this purpose we utilize the equivalence between the Helmholtz equation of our graded flat lens and the quantum-mechanical radial Schrödinger equation with Coulomb potential, furnishing the results in the form of Kummer confluent hypergeometric functions. Our approach allows for a better physical insight into the operation of our transformation optics-based graded lenses and opens a path toward novel designs and approaches.

  • 36.
    Dalarsson, Mariana
    Department of Physics and Electrical Engineering, Linnaeus University, 351 95 Växjö, Sweden.
    General theory of wave propagation through graded interfaces between positive- and negative-refractive-index media2017Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, nr 4, artikel-id 043848Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The introduction of metamaterials and transformation optics has brought the possibilities for manipulating electromagnetic waves to an unprecedented level, suggesting applications like super-resolution imaging, cloaking, subwavelength focusing, and field localization. The refractive index of metamaterial structures in transformation optics typically has to be spatially graded. This paper presents a full analytical method for description of the field propagation through composites with gradient refractive index. The remarkable property of this approach is that it gives explicit general expressions for the field intensity and transmission and reflection coefficients, without reference to any boundary conditions. This opens a possibility for a novel fundamental theory of a number of important electromagnetic phenomena. The method enables calculation of wave propagation parameters within structures with arbitrary losses, arbitrary spectral dispersions, and arbitrary slopes of permittivity and permeability gradients, from mild to abrupt.

  • 37. Nordebo, Sven
    et al.
    Dalarsson, Mariana
    Department of Physics and Electrical Engineering, Linnus University, Växjö, 351 95, Sweden.
    Ivanenko, Yevhen
    Sjöberg, Daniel
    Bayford, Richard
    On the physical limitations for radio frequency absorption in gold nanoparticle suspensions2017Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, nr 15, artikel-id 155401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a study of the physical limitations for radio frequency absorption in gold nanoparticle (GNP) suspensions. A spherical geometry is considered consisting of a spherical suspension of colloidal GNPs characterized as an arbitrary passive dielectric material which is immersed in an arbitrary lossy medium. A relative heating coefficient and a corresponding optimal near field excitation are defined, taking the skin effect of the surrounding medium into account. The classical Mie theory for lossy media is also revisited, and it is shown that the optimal permittivity function yielding a maximal absorption inside the spherical suspension is a conjugate match with respect to the surrounding lossy material. A convex optimization approach is used to investigate the broadband realizability of an arbitrary passive material to approximate the desired conjugate match over a finite bandwidth, similar to the approximation of a metamaterial. A narrowband realizability study shows that for a surrounding medium consisting of a weak electrolyte solution, the electromagnetic heating, due to the electrophoretic (plasmonic) resonance phenomena inside the spherical GNP suspension, can be significant in the microwave regime, provided that the related Drude parameters can be tuned into (or near to) resonance. As a demonstration, some realistic Drude parameters are investigated concerning the volume fraction, mass, and friction constant of the GNPs. The amount of charge that can be accommodated by the GNPs is identified as one of the most important design parameters. However, the problem of reliably modelling, measuring and controlling the charge number of coated GNPs is not yet fully understood, and is still an open research issue in this field. The presented theory and related physical limitations provide a useful framework for further research in this direction. Future research is also aimed at an expansion towards arbitrary suspension geometries and the inclusion of thermodynamical analysis.

  • 38.
    Dalarsson, Mariana
    et al.
    Department of Physics and Electrical Engineering, Linnæus University, 351 95 Växjö, Sweden.
    Nordebo, Sven
    Department of Physics and Electrical Engineering, Linnæus University, 351 95 Växjö, Sweden.
    Sjöberg, Daniel
    Department of Electrical and Information Technology, Lund University, Box 118, 221 00 Lund, Sweden..
    Optimal plasmonic resonances for small arbitrarily shaped particles in lossy media2017Ingår i: 2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2017Konferensbidrag (Refereegranskat)
    Ladda ner fulltext (pdf)
    fulltext
  • 39. Nordebo, Sven
    et al.
    Dalarsson, Mariana
    Department of Physics and Electrical Engineering, Linnœus University, Växjö, 351 95, Sweden.
    Ivanenko, Yevhen
    Sjoberg, Daniel
    Bayford, Richard
    Parameter studies on optimal absorption and electrophoretic resonances in lossy media2017Ingår i: 2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017, Institute of Electrical and Electronics Engineers (IEEE) , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper summarizes and elaborates on some new results on the optimal absorption in small spherical suspensions based on electrophoretic (plasmonic) resonances and lossy surrounding media. The main application here is to study the physical limitations for radio frequency absorption in gold nanoparticle (GNP) suspensions and its potential to achieve GNP targeted hyperthermia in cancer therapy. Numerical parameter studies are included to demonstrate the analysis approach.

  • 40.
    Dalarsson, Nils
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Dalarsson, Mariana
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Tassin, P.
    Jaksic, Z.
    Phase integral approach to wave propagation in continuously graded models of flat lenses2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate the electrodynamics of structures incorporating nanocomposites with negative dielectric permittivity and magnetic permeability, the popular 'left-handed metamaterials'. We obtain analytical solutions to the Helmholtz equation for gradient-index interfaces between the positive and negative index part. We derive expressions for the field intensity as well as for the transmission- and reflection-coefficients, assuming that the graded region across the interface is smaller than the operating wavelength. We then compare the analytical results with the numerical results obtained by the Transfer Matrix Method (TMM). The model allows for arbitrary frequency dependencies and lossy media.

  • 41. Nordebo, Sven
    et al.
    Dalarsson, Mariana
    Department of Physics and Electrical Engineering, Linnæ Us University, Växjö, 351 95, Sweden.
    Khodadad, Davood
    Müller, Beat
    Waldmann, Andreas D
    Becher, Tobias
    Frerichs, Inez
    Sophocleous, Louiza
    Sjöberg, Daniel
    Seifnaraghi, Nima
    Bayford, Richard
    A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing2018Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, nr 20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Classical homogenization theory based on the Hashin-Shtrikman coated ellipsoids is used to model the changes in the complex valued conductivity (or admittivity) of a lung during tidal breathing. Here, the lung is modeled as a two-phase composite material where the alveolar air-filling corresponds to the inclusion phase. The theory predicts a linear relationship between the real and the imaginary parts of the change in the complex valued conductivity of a lung during tidal breathing, and where the loss cotangent of the change is approximately the same as of the effective background conductivity and hence easy to estimate. The theory is illustrated with numerical examples based on realistic parameter values and frequency ranges used with electrical impedance tomography (EIT). The theory may be potentially useful for imaging and clinical evaluations in connection with lung EIT for respiratory management and control.

  • 42. Nordebo, S.
    et al.
    Dalarsson, Mariana
    Department of Physics and Electrical Engineering, Linnæus University, Sweden.
    Gustafsson, M.
    Sjoberg, D.
    On the optimal plasmonic resonances in lossy media2018Ingår i: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018, Institute of Electrical and Electronics Engineers (IEEE) , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    An optimal plasmonic resonance is derived for small homogeneous and isotropic inclusions in a lossy surrounding medium. The optimal resonance is given in terms of any particular eigenmode (electrostatic resonance) associated with the double-layer potential for a smooth, but otherwise arbitrary surface.

  • 43. Ivanenko, Yevhen
    et al.
    Dalarsson, Mariana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik.
    Nordebo, Sven
    Bayford, Richard
    On the Plasmonic Resonances in a Layered Waveguide Structure2018Ingår i: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018, Institute of Electrical and Electronics Engineers (IEEE) , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    An optimal plasmonic resonance and the associated Fröhlich resonance frequency are derived for a thin layer in a straight waveguide in TM mode. The layer consists of an arbitrary composite material with a Drude type of dispersion. The reflection and transmission coefficients of the layer are analyzed in detail. To gain insight into the behavior of a thin plasmonic layer, an asymptotic expansion to the first order is derived with respect to the layer permittivity.

  • 44.
    Norgren, Martin
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    de Saracho, Irene Ortiz
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Dalarsson, Mariana
    Linnaeus Univ, Fac Technol, Vaxjo, Sweden..
    Perturbation Approach to Shape Reconstruction in a Rectangular Waveguide using Experimental Data2018Ingår i: 2018 INTERNATIONAL APPLIED COMPUTATIONAL ELECTROMAGNETICS SOCIETY SYMPOSIUM (ACES), IEEE , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider the inverse problem of reconstructing the shape of a deformation in one of the broad walls of a rectangular waveguide. Assuming a small deformation, resulting in weak scattering, the direct problem is solved using a first order perturbation approach. Hence, the inverse problem becomes linear and is formulated as an equation system for a set of expansion coefficients. The illposedness of the inverse problem is handled with regularization, by adding a penalty term which weight is determined by the L-curve method. The theory is tested on experimental reflection data, using the dominant mode of the waveguide. The reconstructed shape is in qualitative agreement with the true shape, but a detailed resolution cannot be obtained due to insufficient quality of the experimental data. Extensions and improvements of the method are discussed.

  • 45.
    Dalarsson, Mariana
    et al.
    Department of Physics and Electrical Engineering, Linnæus University, Växjö, Sweden.
    Nordebo, Sven
    Department of Physics and Electrical Engineering, Linnæus University, Växjö, Sweden.
    TE-wave propagation in a graded waveguide structure2018Ingår i: Proceedings 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), Institute of Electrical and Electronics Engineers (IEEE) , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 46.
    Dalarsson, Mariana
    et al.
    Department of Physics and Electrical Engineering, Linnaeus University, Växjö, Sweden.
    Nordebo, Sven
    mDepartment of Physics and Electrical Engineering, Linnaeus University, Växjö, Sweden.
    TM-wave propagation in a graded waveguide structure2019Ingår i: Proceedings 2019 URSI International Symposium on Electromagnetic Theory (EMTS), Institute of Electrical and Electronics Engineers (IEEE) , 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 47.
    Dalarsson, Mariana
    et al.
    Department of Electrical and Information Technology, Lund University, Lund, SE-221 00, Sweden.
    Nordebo, Sven
    Department of Physics and Electrical Engineering, Linnaeus University, Växjö, SE-351 95, Sweden.
    TE-wave propagation in graded waveguide structures2020Ingår i: OSA Continuum, E-ISSN 2578-7519, Vol. 3, nr 1, s. 67-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 48.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Svendsen, Brage B.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Exact analytical approach to TM-wave oblique incidence on impedance-matched graded interfaces between RHM and LHM media2021Ingår i: 2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021, Institute of Electrical and Electronics Engineers (IEEE) , 2021Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate TM-wave propagation over an impedance-matched graded interface between a right-handed material (RHM) and a left-handed material (LHM) with graded permittivity and permeability. We assume a lossy case with permittivity and permeability profile changing according to a hyperbolic tangent function along the direction perpendicular to the boundary plane between the two materials. A remarkably simple exact analytical solution to Helmholtz equation is obtained. The exact analytical expression for the field intensity along the graded LHM-RHM structure confirms the expected properties of LHM media. Furthermore, in the special case of normal incidence, we reconfirm that there is an excellent agreement between the present analytical results and numerical simulations.

  • 49.
    Svendsen, Brage B.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Dalarsson, Mariana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Numerical study of TE-wave propagation in waveguides with graded plasmonic obstacles2021Ingår i: 2021 IEEE USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2021: Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2021, s. 90-91Konferensbidrag (Refereegranskat)
    Abstract [en]

    We study transmission, reflection and absorption phenomena in a hollow waveguide of arbitrary cross section, with an inserted graded dielectric layer and TE-wave propagation. We compare the numerical results for the power transmission, reflection and absorption coefficients, obtained using the software COMSOL Multiphysics, with the corresponding results obtained using exact analytic formulae. The results of the present numerical study indicate an excellent agreement with the corresponding exact analytical results. The method proposed in this paper gives directly applicable results that do not require cascading and mode-matching. At the same time, our method has the advantage of being able to model smooth material transitions, that are more realistic in several applications.

  • 50.
    Dalarsson, Mariana
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik.
    Ivanenko, Yevhen
    Linnaeus Univ, Fac Technol, Dept Phys & Elect Engn, S-35195 Växjö, Sweden.;Blekinge Inst Technol, Dept Math & Nat Sci, S-37179 Karlskrona, Sweden..
    Nordebo, Sven
    Linnaeus Univ, Fac Technol, Dept Phys & Elect Engn, S-35195 Växjö, Sweden..
    Wave propagation in waveguides with graded plasmonic obstacles2021Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 38, nr 1, s. 104-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

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