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  • 251.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Asenov, T.
    Doncov, N.
    Lossy transmision with arbitrary gradient permittivity and permeability and constant impedance throughout the structure2013In: 2013 11th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Services, TELSIKS 2013, IEEE , 2013, p. 25-28Conference paper (Refereed)
    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.

  • 252.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Asenov, Tatjana
    Doncov, Nebojsa
    Arbitrary Loss Factors In The Wave Propagation Between RHM And LHM Media With Constant Impedance Throughout The Structure2013In: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 137, p. 527-538Article in journal (Refereed)
    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.

  • 253.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    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 segments2013In: Journal of Nanophotonics, ISSN 1934-2608, Vol. 7, p. 073086-Article in journal (Refereed)
    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.

  • 254.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Dalarsson, Nils
    KTH.
    Jaksic, Z.
    Analytical approach to lossy wave propagation through a graded interface containing negative index material2011In: Int. Conf. Telecommun. Mod. Satell., Cable Broadcast. Serv., TELSIKS - Proc. Pap., 2011, p. 39-42Conference paper (Refereed)
    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. © 2011 IEEE.

  • 255.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    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 structure2012In: Journal of Optics, ISSN 2040-8978, E-ISSN 2040-8986, Vol. 14, no 6, p. 065102-Article in journal (Refereed)
    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.

  • 256.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jaksic, Z.
    Lossy gradient index metamaterial with general periodic permeability and permittivity: The case of constant impedance throughout the structure2012In: Proceedings Of Progress In Electromagnetics Research Symposium (PIERS 2012), Electromagnetics Academy , 2012, p. 190-194Conference paper (Refereed)
    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.

  • 257.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    Jaksic, Zoran
    Exact Analytical Solution for Fields in a Lossy Cylindrical Structure with Linear Gradient Index Metamaterials2015In: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 151, p. 109-117Article in journal (Refereed)
    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.

  • 258.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jaksic, Zoran
    Lossy gradient index metamaterial with sinusoidal periodicity of refractive index: case of constant impedance throughout the structure2011In: J NANOPHOTONICS, ISSN 1934-2608, Vol. 5, p. 051804-Article in journal (Refereed)
    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.

  • 259.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tassin, Philippe
    Analytical solution for wave propagation through a graded index interface between a right-handed and a left-handed material2009In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 8, p. 6747-6752Article in journal (Refereed)
    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.

  • 260.
    Dalarsson, Mariana
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tassin, Philippe
    Jaksic, Zoran
    Exact analytical solution for oblique incidence on a graded index interface between a right-handed and a left-handed material2009In: Journal of Optoelectronics and Biomedical Materials, ISSN 2066-0049, Vol. 1, no 4, p. 345-352Article in journal (Refereed)
    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.

  • 261.
    Dalarsson, Masoud
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mittra, R.
    Analytical approach to modeling flat lenses with continuously graded profiles2015In: 2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2015 - Proceedings, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    In this work we present an analytical approach to deriving the field solutions for a class of flat lenses that have attracted the attentions of antenna designers and researchers alike. The lens designs typically consist of a number of layers of graded index dielectrics, whose properties may vary in both the radial and longitudinal directions. The fields propagating in the longitudinal direction through the central layer primarily contribute to the bulk of the phase, while the side layers act as matching layers and help reduce the reflections originating at the interfaces of the middle layer. We model such lenses as compact composites with material properties characterized by continuous permittivity and permeability functions, which tend asymptotically to unity at the boundaries of the composite cylinder.

  • 262. Dalarsson, Nils
    et al.
    Dalarsson, Mariana
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Golubovic, Leonardo
    Introductory Statistical Thermodynamics2011Book (Other academic)
    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.

  • 263.
    Dalarsson, Nils
    et al.
    KTH.
    Dalarsson, Mariana
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Golubovic, Leonardo
    Introductory Statistical Thermodynamics2011Book (Other academic)
    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.

  • 264.
    Dalarsson, Nils
    et al.
    KTH, School of Electrical Engineering (EES).
    Dalarsson, Mariana
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tassin, P.
    Jaksic, Z.
    General analytical treatment of the graded interfaces with negative-index nanocomposites2009In: Proceedings of the International Conference Days on Diffraction, DD 2009, IEEE Press, 2009, p. 56-60Conference paper (Refereed)
    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.

  • 265.
    de la Roche, Guillaume
    et al.
    Mindspeed Technologies, France.
    Alayon Glazunov, AndresKTH, School of Electrical Engineering (EES), Electromagnetic Engineering.Allen, BenUniversity of Bedfordshire, United Kingdom.
    LTE-Advanced and Next Generation Wireless Networks: Channel Modelling and Propagation2012Collection (editor) (Refereed)
    Abstract [en]

    LTE- A and Next Generation Wireless Networks: Channel Modeling and Performance describes recent advances in propagation and channel modeling necessary for simulating next generation wireless systems. Due to the radio spectrum scarcity, two fundamental changes are anticipated compared to the current status. Firstly, the strict reservation of a specific band for a unique standard could evolve toward a priority policy allowing the co-existence of secondary users in a band allocated to a primary system. Secondly, a huge increase of the number of cells is expected by combining outdoor base stations with smaller cells such as pico/femto cells and relays. This evolution is accompanied with the emergence of cognitive radio that becomes a reality in terminals together with the development of self-organization capabilities and distributed cooperative behaviors. The book is divided into three parts: Part I addresses the fundamentals (e.g. technologies, channel modeling principles etc.). Part II addresses propagation and modeling discussing topics such as indoor propagation, outdoor propagation, etc. Part III explores system performance and applications (e.g. MIMO Over-the-air testing, electromagnetic safety, etc).

  • 266. Dejak, S. I.
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Long-time dynamics of variable coefficient modified Korteweg-de Vries solitary waves2006In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 47, no 7Article in journal (Refereed)
    Abstract [en]

    We study the long-time behavior of solutions to the Korteweg-de Vries-type equation partial derivative(t)u=-partial derivative(x)(partial derivative(2)(x)u+f(u)-b(t,x)u), with initial conditions close to a stable, b=0 solitary wave. The coefficient b is a bounded and slowly varying function, and f is a nonlinearity. For a restricted class of nonlinearities, we prove that for long time intervals, such solutions have the form of the solitary wave, whose center and scale evolve according to a certain dynamical law involving the function b(t,x), plus an H-1(R)-small fluctuation. The result is stronger than those previously obtained for general nonlinearities f.

  • 267. Diallo, C. D.
    et al.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Valerio, G.
    Legay, H.
    Sauleau, R.
    Parallel-plate-waveguide luneburg lens through a holey plate metasurface2015In: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    This paper presents a parallel plate waveguide (PPW) Luneburg lens designed using an array of subwavelength circular holes etched on a metallic plate printed on a dielectric substrate. Variation of the hole radius modulates the effective permittivity. The lens operates in the Ka band of frequencies in a quasi-TEM mode. Easy to implement and low cost, the lens could be a good candidate as a lens-like beamformer for low loss multiple beam applications.

  • 268.
    Diendorfer, G.
    et al.
    Austrian Electrotechnical Association ÖVE, Vienna.
    Zhou, Helin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, H.
    Austrian Electrotechnical Association (OVE), Vienna, Austria.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Review of upward positive and bipolar lightning flashes at the Gaisberg Tower2011In: 2011 7th Asia-Pacific International Conference on Lightning (APL), 2011, p. 263-267Conference paper (Refereed)
    Abstract [en]

    First instrumentation for lightning measurements at the Gaisberg Tower (GBT) has been installed in 1998. During the 10-years period from 2000-2009 a total of 652 lightning events have been recorded. Vast majority of the lightning to the GBT was upward initiated and only one record is a candidate for a downward flash when the recorded current waveform is used for discrimination between upward and downward lightning. 3% (21/652) of the flashes were bipolar and about the same number of 4% (26/652) were positive. 73% of positive and 63% of bipolar lightning was triggered by the GBT during cold season in Austria.

  • 269. Ding, Fei
    et al.
    Cui, Yanxia
    Ge, Xiaochen
    Jin, Yi
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ultra-broadband microwave metamaterial absorber2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 10, p. 103506-Article in journal (Refereed)
    Abstract [en]

    A microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated. It is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids. These pyramids possess resonant absorption modes at multi-frequencies, of which the overlapping leads to the total absorption of the incident wave over an ultra-wide spectral band. The experimental absorption at normal incidence is above 90% in the frequency range of 7.8-14.7 GHz, and the absorption is kept large when the incident angle is smaller than 60 degrees. The experimental results agree well with the numerical simulation.

  • 270. Ding, Fei
    et al.
    Jin, Y.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ultra-broadband near-infrared metamaterial absorber2012In: Asia Commun. Photonics Conf., 2012Conference paper (Refereed)
    Abstract [en]

    A near-infrared wide-band polarization-insensitive absorber is demonstrated. It is composed of two-dimensional titanium disk arrays and a gold plate. The absorption at normal incidence is above 90% in the range of 164.2THz to 345.2 THz.

  • 271. Ding, Fei
    et al.
    Jin, Yi
    Li, Borui
    Cheng, Hao
    Mo, Lei
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang Univ, China.
    Ultrabroadband strong light absorption based on thin multilayered metamaterials2014In: Laser & Photonics reviews, ISSN 1863-8880, E-ISSN 1863-8899, Vol. 8, no 6, p. 946-953Article in journal (Refereed)
    Abstract [en]

    Light absorbers have drawn intensive attention as crucial components for solar-energy harvesting, thermal emission tailoring, modulators, etc. However, achievement of light absorbers with wide bandwidth remains a challenge thus far. Here, a thin, unprecedentedly ultrabroadband strong light absorber is proposed and experimentally demonstrated, which consists of periodic taper arrays constructed by an alumina-chrome multilayered metamaterial (MM) on a gold substrate. This MM can change from a hyperbolic material to an anisotropic dielectric material at different frequency ranges and the special material features are the fundamental origins of the ultrabroadband absorption. The absorber is quite insensitive to the incident angle, and can be insensitive to the polarization. One two-dimensional periodic array of 400-nm height MM tapers is fabricated. The measured absorption is over 90% over almost the entire solar spectrum, reaching an average level of 96%, and remains high (above 85%) even in the longer-wavelength range till 4 m. The proposed absorbers open up a new avenue to realize broadband thin light-harvesting structures.

  • 272. Ding, Fei
    et al.
    Mo, Lei
    Zhu, Jianfei
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lithography-free, broadband, omnidirectional, and polarization-insensitive thin optical absorber2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 6, article id 061108Article in journal (Refereed)
    Abstract [en]

    We have proposed and experimentally demonstrated a lithography-free, broadband, thin optical absorber composed of planar multilayered dielectric and metal films, which can cover the total visible wavelength range with simulated and experimental absorption efficiencies higher than 90%. Moreover, the absorption is insensitive to the polarization and angle of incidence. Such a planar device is much easier to fabricate compared with other broadband absorbers with complicated structures and may have potential applications in solar energy harvesting and controllable thermal emission.

  • 273. Ding, Fei
    et al.
    Wang, Zhuoxian
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China.
    Shalaev, Vladimir M.
    Kildishev, Alexander V.
    Broadband High-Efficiency Half-Wave Plate: A Supercell-Based Plasmonic Metasurface Approach2015In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, no 4, p. 4111-4119Article in journal (Refereed)
    Abstract [en]

    We design, fabricate, and experimentally demonstrate an ultrathin, broadband half-wave plate in the near-infrared range using a plasmonic metasurface. The simulated results show that the linear polarization conversion efficiency is over 97% with over 90% reflectance across an 800 nm bandwidth. Moreover, simulated and experimental results indicate that such broadband and high-efficiency performance is also sustained over a wide range of incident angles. To further obtain a background-free half-wave plate, we arrange such a plate as a periodic array of integrated supercells made of several plasmonic antennas with high linear polarization conversion efficiency, consequently achieving a reflection-phase gradient for the cross-polarized beam. In this design, the anomalous (cross-polarized) and the normal (copolarized) reflected beams become spatially separated, hence enabling highly efficient and robust, background-free polarization conversion along with broadband operation. Our results provide strategies for creating compact, integrated, and high-performance plasmonic circuits and devices.

  • 274. Ding, J. F.
    et al.
    Zhang, A. P.
    Shao, L. Y.
    Yan, J. H.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Fiber-taper seeded long-period grating pair as a highly sensitive refractive-index sensor2005In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 17, no 6, p. 1247-1249Article in journal (Refereed)
  • 275. Ding, Jiechen
    et al.
    Hu, Jun
    Khan, Salman Naeem
    Ying, Zhinong
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    An ultra-wideband monopole antenna of small size2006In: 2006 IEEE International Workshop on Antenna Technology: Small Antennas and Novel Metamaterials (IWAT), NEW YORK: IEEE , 2006, p. 61-63Conference paper (Refereed)
  • 276. Ding, Jiechen
    et al.
    Lin, Zhili
    Ying, Zhinong
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A compact ultra-wideband slot antenna with multiple notch frequency bands2007In: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 49, no 12, p. 3056-3060Article in journal (Refereed)
  • 277.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bissal, Ara
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gati, Rudolf
    EFFECT OF POLYMER BASED NANOCOMPOSITES ON THE ELECTRICAL ARCS IN AIR2015In: 2015 42ND IEEE INTERNATIONAL CONFERENCE ON PLASMA SCIENCES (ICOPS), ISSN 0730-9244Article in journal (Other academic)
  • 278.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bissai, A.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Gati, R.
    Spectroscopic investigations of the ablated species from the polymers exposed to electric arcs in air2015In: 2015 3rd International Conference on Electric Power Equipment - Switching Technology, ICEPE-ST 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 337-340Conference paper (Refereed)
    Abstract [en]

    Polymeric walls have been widely used in the last decades to improve the arc interruption process in electrical switching applications. This improvement is achieved by the evaporation (ablation) of the polymeric walls due to the highly energetic radiation generated by the electrical arcs. This experimental study deals with polymeric walls that are exposed to the electrical arcs generated between a 5 mm air gap with prospective current of 1.4 kA. In this paper, two different techniques are discussed aiming at the identification of the dominant ablated species produced during the arc interruption process, namely Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis coupled with Fourier transform infrared analysis of evolved gases (EGA). In addition, the morphological and chemical changes on the surface of the exposed polymeric walls are analyzed by microscopical techniques.

  • 279.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Gati, R.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Improving Uv Radiation Absorption by Copper Oxide NPs/PMMA Nanocomposites for Electrical Switching Applications2015In: Powder metallurgy and metal ceramics, ISSN 1068-1302, E-ISSN 1573-9066, Vol. 54, no 7-8, p. 397-401Article in journal (Refereed)
    Abstract [en]

    Nanocomposites based on the radiation absorbing polymer (PNCs) are of interest for a variety of applications including circuit breakers, UV-shielding windows, contact lenses, and glasses among others. Such PNCs can be made by incorporating suitable radiation absorbing nanoparticles into a polymeric matrix by in situ polymerization. In this study, spherical nanoparticles (5-6 nm) of oleic acid (OA) surface modified cupric oxide (CuO) are synthesized and used to improve the ultra-violet (UV) radiation absorption property of a polymer matrix, i.e., polymethylmethacrylate (PMMA). The synthesis of spherical CuO nanoparticles, surface modification using OA, dispersion of CuO nanoparticles with different concentrations in PMMA, and UV radiation absorption property of the resultant PNC are investigated. Two different PNCs are produced using OA modified CuO nanoparticles with different concentrations. As synthesized CuO nanoparticles and OA modified CuO nanoparticles are examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. The UV absorption edges are evaluated from the UV-Vis absorption spectra by using UV-Visible absorption spectroscopy. The results show that the UV radiation absorption of the PNC with higher concentration of CuO nanoparticles is improved compared with PMMA and the absorption edge moved towards longer wavelengths i.e., from 271 to 281 nm. These PNCs are successful in arc interruption process by absorbing a broad range of radiation emitted from high-energy copper arcs produced in the circuit breakers.

  • 280.
    Dubickas, Valentinas
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Development of on-line diagnostic methods for medium voltage XLPE power cables2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    On-line diagnostics of power system components is an important area since it allows the diagnostics to be performed at regular intervals during the normal operation of the components. This combined with reliability centered maintenance could lead to reduced customer outages. In this thesis the on-line diagnostic methods for medium voltage cross-linked polyethylene (XLPE) cables are investigated based on Time Domain Reflectometry (TDR).

    Degradation of XLPE insulated power cables by water-trees (WT) is a primary cause of failure of these cables. The detection of WT and information about the severity of the degradation can be obtained with off-line measurements using dielectric spectroscopy.  In many situations only a limited part of the cable may be degraded by the WT. In such a situation a method for localization of this WT section would be desirable.

    The developed high frequency measurements superimposed on HV system is presented. It was used to measure the propagation constant of the WT aged cables as a function of the applied HV. This was done in order to study the diagnostic criteria, which could be used for on-line TDR diagnostics of WT aged cables.

    A physically based dielectric model of WT was developed in order to explain qualitatively and quantitatively the permittivity and loss of WT at different frequencies and voltages.

    The sensors applicable for the on-line TDR were investigated in terms of sensitivity and bandwidth. High frequency models were built and the simulation results in frequency and time domains were verified by measurements.

    The developed on-line TDR systems are presented. Their applicability to detect water penetration under the cable sheath and localize the broken screen wires was investigated during the measurements in laboratory environment.

    The results of field measurements with on-line TDR are presented. Variations due to load cycling of the cable were observed, where an increase in the cable temperature cause an increase of the pulse propagation velocity in the cable. The temperature dependent wave propagation in the cable is investigated and explained by modeling.

  • 281.
    Dubickas, Valentinas
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On-line time domain reflectometry diagnostics of medium voltage XLPE power cables2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Degradation of XLPE insulated power cables by water-trees is a primary cause of failure of these cables. The detection of water-trees and information about the severity of the degradation can be obtained with off-line measurement using dielectric spectroscopy. In many situations only a limited part of the cable may be degraded by the water-trees. In such a situation a method for localization of this water-treed section would be desirable. On-voltage Time Domain Reflectometry (TDR) diagnostics proved to be capable of localizing the water-tree degraded sections of the cable. The possibility of using on-voltage TDR as a diagnostic method opens up as a further step for the development of an on-line TDR method where the diagnostics are performed using pre-mounted sensors on the operating power cable. The benefits with such a method are: ability to perform diagnostics without disconnecting the cable from a power grid; the diagnostics performed during a longer period of time could give an extra information; no need for an external high-voltage supply unit.

    In this thesis the sensors for the on-line TDR are investigated in terms of sensitivity and bandwidth. High frequency models were built and the simulation results in frequency and time domains were verified by measurements. Results of the on-voltage TDR measurements on the degraded XLPE cables in laboratory as well as on-site are presented.

    The on-line TDR system and the results of a four-days on-line measurement sequence are presented. Variations due to load cycling of the cable were observed, where an increase in the cable temperature cause an increase of the pulse propagation velocity in the cable.

    A method has been developed for high frequency characterization of power cables with twisted screen wires, where the measurements are performed using inductive strip sensors. This technique allows the high frequency parameters of the selected section of the cable to be extracted. The high frequency parameters are extracted from frequency domain measurements of S-parameters as well as from TDR measurements.

  • 282.
    Dubickas, Valentinas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Dielectric model of water trees in an XLPE cable2008In: International Symposium on Electrical Insulating Materials (ISEIM 08), Yokkaichi, Japan, 2008, p. 448-451Conference paper (Refereed)
    Abstract [en]

    In this paper a water-tree degraded insulation is modeled as a matrix composed of cubic cells. In the model there are three types of cells: pure XLPE, XLPE with water inclusion and the XLPE cell with a cylindrical water channel. Voltage dependant dielectric properties of the water-trees are modeled by an elongation of the inclusions and appearance of the conducting channels caused by the Maxwell stress. Afterwards the modeled effective permittivity of the insulation matrix is compared with the dielectric spectroscopy measurements of a field aged XLPE cable.

  • 283.
    Dubickas, Valentinas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    High-Frequency Model of the Rogowski Coil With a Small Number of Turns2007In: IEEE Transactions on Instrumentation and Measurements, ISSN 0018-9456, Vol. 56, no 6, p. 2284-2288Article in journal (Refereed)
    Abstract [en]

    In this paper, the Rogowski coil is modeled as adistributed-element transmission line. The elements in the distributedtransmission line are modeled using physically basedequations. It allows self and transfer impedances of the Rogowskicoil to be modeled using the physical dimensions and the materialproperties of the coil. The models of the impedances were verifiedby measurements in the frequency domain on three Rogowskicoils. The coils mounted on the power cable were modeled andsimulated in the time domain and afterward compared with themeasurements.

  • 284.
    Dubickas, Valentinas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On-line time domain reflectometry measurements of temperature variations of an XLPE power cable2006In: 2006 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Kansas City, Missouri, USA, 2006, p. 47-50Conference paper (Refereed)
    Abstract [en]

    In this paper an on-line time domainreflectometry system and a four-days measurementssequence are presented. Detected pulse velocityvariations are attributed to temperature variations of thecable caused by a load cycling. The changes in the pulsevelocity are verified by propagation constantmeasurements of a power cable at differenttemperatures in 300 kHz - 500 MHz frequency range.Also an influence of temperature dependentsemiconducting screens and XLPE insulation to thechanges in the cable's capacitance is investigated.

  • 285.
    Dubickas, Valentinas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Technique Employing Inductive Coupler for Propagation Constant Extraction on Power Cables with Twisted Screen Wires2005In: Proceedings of the Nordic Insulation Symposium, p. 242-245Article in journal (Refereed)
    Abstract [en]

    This paper investigates a new propagation constant measuring technique in which an inductive coupler allows only the selected part of the cable to be measured. The propagation constants are extracted from frequency and time domain measurements. The extracted propagation constants from measurements with an inductive coupler are compared with the reference propagation constant obtained from direct measurements on the cable. The dependence of the extracted propagation constant accuracy on the measured cable part length is investigated.

  • 286.
    Dubickas, Valentinas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Temperature influence on wave propagation in XLPE power cables: on-line and laboratory measurements2009Article in journal (Other academic)
    Abstract [en]

    This paper investigates the influence of temperature on the wave propagation in medium voltage XLPE power cables. During an on-line time domain reflectometry measurements a periodicity of the pulse velocity was observed. These variations are attributed to the temperature changes of the cable caused by the load cycling. The results of the on-line measurements were verified by laboratory measurements of the propagation constant as a function of temperature in the 0.3 – 500 MHz frequency range. It is shown that the changes in the propagation constant are mainly caused by the temperature dependent permittivities of the semiconducting shields and the XLPE insulation.

  • 287.
    Duvette, Hadrien
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Management of particle contamination in DC GIS for industrial application2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Modern politics wants decarbonized energy sources. Many power plants of renewable

    energy are expected to be built. A DC grid may interconnect the largest “green”

    power plants. A grid requires substations. Among the technologies of substations

    there is the Gas-Insulated-Systems (GIS). As a result the market of DC-GIS may

    start up in the coming years. One of the issues is to address the presence of particles

    inside a DC-GIS. The literature do not provide any general concept to manage the

    particle presence inside a DC-GIS. The result of this thesis is a method to predict

    where a particle is supposed to go when the voltage is applied. Thanks to this

    report the reader is aware of the physics acting on a conducting particle and learns

    about a method to predict the direction of a particle. The method relies on several

    documents which are defined in this report. A first document is a table which

    provides with the relevant stereotypes of the particles. A second document is a

    subsection which defines several possible kind of motion which are associated to a

    strategy which predicts the direction of motion. A third document is a graphical

    representation of the possible motion depending on the electrical field. A fourth

    document is the set of graphical representations of the forces which can drive the

    5

    particles. The method was found out after a deep observation and analysis of some

    videos showing particles in a DC field. The thesis shows some of the observations

    and describes the conditions of experimentation. To finish with, the report provides

    with 5 solutions for the problem of the presence of particle in a GIS.

     

  • 288.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mitchell-Thomas, R. C.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lens antennas using QCTO technique2015In: 2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2015 - Proceedings, IEEE , 2015, p. 168-Conference paper (Refereed)
    Abstract [en]

    Quasi Conformal Transformation Optics (QCTO) is employed here to produce 3D gradient-index lenses. These lenses are able to improve radiation properties of conventional antennas, such as gain, side lobe levels and cross polarization.

  • 289.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bespoke Lenses Based on Quasi-Conformal Transformation Optics Technique2017In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, no 5, p. 2256-2264Article in journal (Refereed)
    Abstract [en]

    In this paper, a systematic method to design a quasioptimum lens profile based on quasi-conformal transformation optics technique for a given excitation is presented. This method is applied to a number of conventional antennas, such as an aperture and a log-spiral slot. In all these configurations, an increase of the directivity is observed. Furthermore, using this method, a quasi-optimum graded index lens for a broadband enhanced leaky slot excitation is designed and the results are compared with a hyperhemispherical lens with and without matching layers. Our proposed methodology demonstrates to be able to increase the directivity, to reduce the sidelobes and the cross polarization in a broad bandwidth from 20 to 70 GHz. Due to the continuously changed dielectric constant of the lens profile, reflections are also reduced considerably inside the lens.

  • 290.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rajo-Iglesias, E.
    Design of microwave components in groove gap waveguide technology implemented by holey EBG2017In: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 746-748, article id 7928587Conference paper (Refereed)
    Abstract [en]

    In this paper, the feasibility of the implementation of microwave components in groove gap waveguide technology by glide-symmetry holey EBG is discussed. Using this technology, microwave components and antennas which were previously designed for hollow metallic waveguides can be manufactured in a cost-effective way at high frequencies. To show the viability of the proposed solution a phase shifter and a mode converter are designed as examples of typical components for antenna systems.

  • 291.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rajo-Iglesias, Eva
    Design Guidelines for Gap Waveguide Technology Based on Glide-Symmetric Holey Structures2017In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 27, no 6, p. 542-544Article in journal (Refereed)
    Abstract [en]

    The behavior of a glide-symmetric holey periodic structure as electromagnetic bandgap is studied in this letter. A number of numerical simulations have been carried out in order to define the importance of each constituent parameter of the unit cell. Our proposed structure finds potential application in antennas and circuits based on gap waveguide technology for the millimeter band. The experimental verifications confirm the effects previously analyzed with the numerical studies.

  • 292.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rajo-Iglesias, E.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wideband glide-symmetric holey structures for gap-waveguide technology2017In: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1658-1660, article id 7928356Conference paper (Refereed)
    Abstract [en]

    In this paper, the stop-band of two different holey glide-symmetric EBG lattices is studied. The results show that glide-symmetric EBG structures have potential to achieve wide stop-bands by polygonal lattices. Potential application of the proposed EBG structure in gap-waveguide technology is discussed in the second part of the paper.

  • 293.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rajo-Iglesias, E.
    Sipus, Z.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Low-cost metasurface using glide symmetry for integrated waveguides2016In: 2016 10th European Conference on Antennas and Propagation, EuCAP 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 7481261Conference paper (Refereed)
    Abstract [en]

    A novel Electromagnetic Band Gap (EBG) structure based on an off-shifted periodic metasurface is presented here. This technique can be employed for packaging of electrical circuits and gap waveguide technology. The proposed structure is easy to manufacture since it only requires drilling holes in metallic plates, reducing the cost when compared to previous works based on other textured surfaces.

  • 294.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rajo-Iglesias, Eva
    Sipus, Zvonimir
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Cost-Effective Gap Waveguide Technology Based on Glide-Symmetric Holey EBG Structures2018In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, no 2, p. 927-934Article in journal (Refereed)
    Abstract [en]

    We present a novel electromagnetic bandgap (EBG) structure, which can be used to manufacture low-cost waveguiding structures at high frequencies. The unit cell of the proposed EBG consists of glide-symmetric holes in parallel plate waveguide. Using this unit cell in groove gap waveguide technology has a number of advantages over pin-type EBG at high frequencies, such as acquiring higher accuracy because of larger periodicity as well as an easier and cheaper manufacturing process. The performance of the proposed waveguiding structure is demonstrated using both a straight and a double 90 degrees bent lines through simulation and measurement.

  • 295.
    Edquist, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electrothermal Design and Analysis of Dielectric TE01-mode Resonator Filters2015Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The use of dielectric resonator filters is very common in the telecommunications

    industry for applications with demanding filtering requirements.

    For high power applications in particular, TE01-mode dielectric

    resonators are often used because of its low losses and excellent

    peak power handling capabilities. The essence of this work is to

    great extent focused around the fact that even a small amount of dissipated

    power can give rise to a large temperature increase if the heat

    transfer is insufficient. A temperature increase due to self-heating

    translates into a degradation of filter performance. Understanding the

    mechanisms behind this degradation is vital in order to compensate

    for these effects. Computer simulations can successfully be used to

    characterise the electrical and thermal behaviour of these devices.

    However, if the filter in question is not properly tuned when running

    the analysis the results will bring little or no value. This work outlines

    an efficient filter design flow based on Port Tuning in order to

    overcome this tuning issue. By carefully studying both a single resonator

    and a realistic filter example using CFD analysis the heat

    transfer mechanisms can be quantified and the dominant terms can

    be identified. Based on these results, a simplified model for the thermal

    analysis can then be established. A coupled analysis including

    electromagnetic, thermal and structural analysis is then demonstrated

    that predicts the performance degradation of the filter response. It is

    also demonstrated how these effects can be compensated for.

  • 296.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Alvehag, Karin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Influence of Ambient Temperature on Transformer Overloading During Cold Load Pickup2013In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 28, no 1, p. 153-161Article in journal (Refereed)
    Abstract [en]

    This paper proposes a method to investigate the socioeconomical aspects of transformer overloading during a cold load pickup (CLPU) in residential areas. The method uses customer damage functions to estimate the cost for their power interruption and a deterioration model to estimate the cost for transformer wear due to the CLPU. A thermodynamic model is implemented to estimate the peak and the duration of cold residential load. A stochastic differential equation is used to capture the volatility of the load and to estimate the probability for transformer overloading. In a numerical example, an optimal cold load pickup for a two-area system is demonstrated where transformer overloading is allowed. In this example, an ambient temperature threshold is identified, where transformer overloading is socioeconomically beneficial.

  • 297.
    Edström, Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modeling Impact of Cold Load Pickup on Transformer Aging Using Ornstein-Uhlenbeck Process2012In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 27, no 2, p. 590-595Article in journal (Refereed)
    Abstract [en]

    Thermostatically controlled devices, such as air conditioners, heaters, and heat pumps may cause cold load pickup (CLPU) problems after a prolonged blackout. This causes an increased load on the power components in the electrical grid. The result is unpredictable aging and increased risk of failure. Quantifying this risk is crucial for efficient asset management for cost-intensive components such as the transformer. This paper presents a new approach to model the loading profile of a CLPU using stochastic differential equations. The realization of the loading profile is used to determine the aging of a transformer. Two models for the deterioration of transformer solid insulation represent the loss of life due to the CLPU. A comparison between two models for the aging of the solid insulation in the transformer is made in a case study. Due to the stochastic behavior of the load, there is a probability for loading the transformer above the recommended ratings, and this probability is estimated with Monte Carlo simulations.

  • 298.
    Ekelund, Maria
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gedde, Ulf W
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Long-term performance of poly(vinyl chloride) cables. Part 1: Mechanical and electrical performances2007In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 92, no 4, p. 617-629Article in journal (Refereed)
    Abstract [en]

    Cables insulated with plasticized poly(vinyl chloride) were aged in air at temperatures between 80 degrees C and 180 degrees C and their conditions were assessed by indenter modulus measurements, tensile testing, infrared (IR) spectroscopy and differential scanning calorimetry (DSC). Electrical testing of oven-aged cable samples was performed in order to relate the electrical functionality during a high-energy line break (HELB) to the mechanical properties and to establish a lifetime criterion. The mechanical data taken at room temperature after ageing could be superimposed with regard to ageing time and temperature. The ageing-temperature shift factor showed an Arrhenius temperature dependence. The jacketing material showed an immediate increase in stiffness (indenter modulus and Young's modulus) and a decrease in the strain at break on ageing; these changes were dominated by loss of plasticizer by migration which was confirmed by IR spectroscopy and DSC. The core insulation showed smaller changes in these mechanical parameters; the loss of plasticizer by migration was greatly retarded by the closed environment, according to data obtained by IR spectroscopy and DSC, and the changes in the mechanical parameters were due to chemical degradation (dehydrochlorination). A comparison of data obtained from this study and data from other studies indicates that extrapolation of data for the jacketing insulation can be performed according to the Arrhenius equation even down to service temperatures (20-50 degrees C). The low-temperature deterioration of the jacketing is, according to this scheme, dominated by loss of plasticizer by migration.

  • 299.
    Ekstedt, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Babu, Sajeesh
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Failure Rate Trends in an Aging Population - Monte Carlo Approach2015In: 23rd International Conference on Electricity Distribution - CIRED 2015, CIRED - Congrès International des Réseaux Electriques de Distribution, 2015Conference paper (Refereed)
    Abstract [en]

    This paper proposes a method to make future failure predictions from input data on population age distribution and failure rates, using a Monte Carlo approach. In contrast to many methods used today, the method in this paper is designed to address multiple properties and assumptions simultaneously, which makes the task complicated. For example, the component population is allowed to be divided into both age and different types. The time-dependent failure rates are defined separately for each individual type, can consist of a combination of multiple different failure rates for separate modes, and can be of practically any shape. Furthermore, a volatility measure for the failure rates is introduced and used to model the uncertainties in failure rate estimates. The method handles investment and reinvestment scenarios as well as different restoration models, such as replacing a failed component with a new component of a different type. As a part of the project, a stand-alone software tool was developed and presented in the paper. In the included case study, the method and the tool are shown to be useful when investigating reinvestment strategies to renew the population and decrease the expected number of future failures. The paper gives the reader useful information and understanding on how the problem of predicting the reliability of the future power system can be addressed and solved.

  • 300.
    Ekstedt, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Categorization and Review of Failure Rate Factors Used in Power Systems2014In: 2014 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2014 - Conference Proceedings, 2014, IEEE Press, 2014Conference paper (Refereed)
    Abstract [en]

    To evaluate the reliability of power systems, good estimates of the failure rates of the included components are needed. Better predictions can be performed if relevant factors that affect the failure rates are used, and an increasing number of models that include different types of factors have been presented recently. This paper proposes a categorization of failure rate factors into seven categories, based on the type of information for the factors. The categorization can be used to map future studies in the context of similar work.  Furthermore, the paper presents a review of a number of publications that uses different factors to model the failure rate of different power system components. The failure rate factors used in the reviewed publications are categorized into the proposed seven categories and a comprehensive summary table is included. The used models and methods to estimate the failure rate in the reviewed publications are also noted in the summary table.

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