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  • 301.
    Elawa, AMR
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Översyn av skyddsanordning samt nollpunkt för fördelningsstationen Fs Myrängen2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This is a report of a Master’s thesis done in behalf of the local network

    in Stockholm, under Fortum Distribution AB. The thesis was to

    conduct a review of a distribution station named Fs Myrängen located in

    Täby. A model was created for the 11 kV network linked to the secondary

    side of Fs Myrängen. Based on this model and using symmetrical components,

    theoretical fault currents (short circuit and ground fault) could

    be calculated. The results of these fault currents are used to investigate

    and develop new settings for relay protection and ground equipment in

    the station. The results of the calculated fault currents were also used

    to investigate unwanted voltages that occurs for grounded parts due to

    earth faults. The value of these unwanted voltages was then compared

    to heavy current regulations developed by the Electrical Safety Authority

    in Sweden. Another element of the work was to create a rehabilitation

    plan for the structure on the 11 kV side of Fs Myrängen, the main goal

    regarding the rehabilitation plan was to investigate the advantages and

    disadvantages that exist at a possible transition to numerical protection

    relays. This was done by making a market overview of the different types

    of numerical protection relays and compare these with the existing analog

    protective device in Fs Myrängen.

    The study showed that protective relay settings should be revised according

    to the recommendations in the report, ground equipment should

    be replaced with a self-regulating type, transformers should be replaced

    due to age and capacity limitations. Regarding a switch to numerical

    protection relays the type REF615 from ABB was recommended, in that

    case the control board in the station should be replaced to a station computer.

    Furthermore should current transformers be replaced to recive a

    desired sensitivity regarding detection of ground faults. The report also

    showed that Fs Myrängen meets the regulations of unwanted voltages over

    grounded parts in distribution stations due to earth faults.

  • 302.
    Ellgardt, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Review of Planar Array Antenna Research at KTH2010In: The Twelth Antennas and propagation Symposium, Kochi, India: Department of Electronics, Cochin University of Science & Technology , 2010Conference paper (Refereed)
  • 303.
    Ellgardt, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Scan Blindness Model for Single-Polarized Tapered-Slot Arrays in Triangular Grids2008In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 56, no 9, p. 2937-2942Article in journal (Refereed)
    Abstract [en]

    A simple model is presented that predicts scan blindness in the E-plane for single polarized tapered-slot arrays where the elements are positioned in a triangular grid. The blindness occurs when the phase progression along the dielectric substrates is equal to the phase progression of a leaky mode in the structure. A simple equation is presented that estimates the frequency at which the scan blindness occurs for a given angle in the E-plane. This equation is derived from a simple representation of the phased array antenna, but includes the dominant effect of this particular class of scan blindness. The method is shown to agree well with computed results obtained with two different numerical codes.

  • 304.
    Ellgardt, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Computing return loss for arbitrary scan directions using limited scan codes for infinite phase arrays2009In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 45, no 13, p. 660-662Article in journal (Refereed)
    Abstract [en]

    Analyzing large phased array antennas using time domain codes is favourable when looking into wideband solutions. This is often done by assuming an infinite array, i.e. a unit cell approach is used. Unfortunately, unit cell based time domain codes using time shifts between cell boundaries have a disadvantage of only being able of analyzing phase shifts corresponding to a beam scanned in the visible space. However, in order to fully characterize the infinite array antenna it is sometimes necessary to compute the active reflection coefficient also for scan directions/phase shifts corresponding to invisible space. Presented in this letter is a new approach on how to do this in a simple manner using unit cell based time domain codes. By extending the size of the computational domain, and include more than one element, phase shifts corresponding to invisible space are included.

  • 305.
    Ellgardt, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Effects on scan blindnesses of an absorbing layer covering the ground plane in a triangular grid single-polarized tapered-slot array2008In: Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE, 2008, p. 2966-2969Conference paper (Refereed)
  • 306.
    Ellgardt, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Skärmningseffektivitet för betongväggar med kolfilament- eller kolfibertillsatser2011In: Electronic environment 2011, 2011, p. 81-82Conference paper (Refereed)
  • 307.
    Ellgardt, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Study of Rectangular Waveguide Elements for Planar Wide-Angle Scanning Phased Array Antennas2005In: Antennas and Propagation Society International Symposium, 2005 IEEE, 2005, p. 815-818Conference paper (Refereed)
    Abstract [en]

    Rectangular waveguide elements in an infinite planar phased array are analysed with respect to wide-angle scanning. Three waveguide geometries are considered: two dual polarized square waveguides and one rectangular waveguide. The waveguides are matched for minimum average reflected power over the scan range. This cost function is shown to give a match suitable for wide-angle scanning

     

  • 308.
    Ellgardt, Anders
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wide-angle scanning wide-band phased array antennas2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis considers problems related to the design and the analysis of wide-angle scanning phased arrays. The goals of the thesis are the design and analysis of antenna elements suitable for wide-angle scanning array antennas, and the study of scan blindness effects and edge effects for this type of antennas. Wide-angle scanning arrays are useful in radar applications, and the designs considered in the thesis are intended for an airborne radar antenna.After a study of the wide-angle scanning limits of three candidate elements, the tapered-slot was chosen for the proposed application.A tapered-slot antenna element was designed by using the infinitive array approach and the resulting element is capable of scanning out to 60° from broadside in all scan planes for a bandwidth of 2.5:1 and an active reflection coefficient less than -10 dB. This design was implemented on an experimental antenna consisting of 256 elements.The predicted performance of the antenna was then verified by measuring the coupling coefficients and the embedded element patterns, and the measurements agreed well with the numerical predictions.Since the radar antenna is intended for applications where stealth is important, an absorbing layer is positioned on top of the ground plane to reduce the radar cross section for the antenna's cross-polarization.This absorbing layer attenuates guided waves that otherwise lead to scan blindness, but does not adversely affect the antenna performance for the desired scan directions and frequencies.The highest frequency limit of the tapered-slot element is set by scan blindnesses. One of these scan blindnesses is found to be unique to tapered-slot elements positioned in triangular grids. This scan blindness is studied in detail and a scan blindness condition is presented and evaluated.The evaluation of the experimental antenna shows that edge effects reduce the H-plane performance of the central elements.These edge effects are further studied and characterized, by comparing the scattering parameters for finite-by-infinite arrays and infinite arrays.In this way it is possible to divide the edge effects into two categories: those caused by finite excitation, and those caused by perturbed currents due to the geometry of the edge. A finite difference time domain code with time shift boundaries is used to compute the active reflection coefficients needed to compute the scattering parameters, but this code cannot directly compute the active reflection coefficient for all the required phase shifts.Hence, an additional method is presented that makes it possible to compute arbitrary phase shifts between the elements using any numerical code with limited scan directions.

  • 309.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, Lars
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Resonance shift due to edge effects in finite-by-infinite monopole arrays2011In: International symposium on antennas and propagation, 2011Conference paper (Refereed)
  • 310.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Månsson, Daniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling Shielding Effectiveness for Composite Walls of Concrete and Carbon Filaments2013In: Progress In Electromagnetics Research M, ISSN 1937-8726, Vol. 28, p. 15-25Article in journal (Refereed)
    Abstract [en]

    Concrete walls reinforced with rebars have poor shielding effectiveness for telecommunication frequencies (frequencies above 0.5 GHz). An effective method to increase the shielding effectiveness of the walls is to increase the complex permittivity of the concrete. This can be done by mixing in thin filaments of a material with high conductivity. One such material is carbon. In this paper the Maxwell Garnett mixing rule is used to model a concrete material with carbon filaments. The shielding effectiveness computed with the mixing rule is found to agree with previously published measurement results.

  • 311.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A study of edge effects in triangular grid tapered-slot arrays using coupling coefficients2010In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 45, p. RS2005-Article in journal (Refereed)
    Abstract [en]

    Edge effects for tapered-slot elements in triangular grid array antennas are studied by using finite difference time domain codes. The S parameters for finite-by-infinite arrays are computed and evaluated for two different edge models and, to evaluate the edge effects, the results are compared with the S parameters for the infinite array. As expected, the largest difference between the results occurs for the elements closest to the edges, because of the missing coupling from nearby elements and the perturbed element currents due to the edge geometry. By using the proposed method it is possible to distinguish between these two edge effects. A method to combine the finite-by-infinite array results and the infinite array results is presented and used to characterize the perturbation caused by the truncation of the infinite array.

  • 312.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Study of Edge Elements in Triangular Grid Tapered-Slot Arrays2010In: International Symposium on Microwaves-2010, 2010Conference paper (Refereed)
  • 313.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edge element evaluation of tapered-slot elements in phased arrays2010In: EuCAP 2010 - The 4th European Conference on Antennas and Propagation, 2010Conference paper (Refereed)
    Abstract [en]

    The edge elements in large phased arrays of tapered-slot elements are analyzed and compared with the infinite array. In large phased arrays the elements that are close to the center of the antenna have similar performance. However, the elements close to an edge will have different coupling coefficients and embedded radiation patterns due to the truncated geometry. In this paper the edge effects in a triangular grid tapered-slot array is studied by using finite-by-infinite arrays. The array is infinite in the direction along the edge and finite in the other direction. The S-parameters for three truncations of the tapered slot element are compared with the infinite array solution for the case when the edge is orthogonal to the E-plane.

  • 314.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Persson, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Characteristics of a broad-band wide-scan fragmented aperture phased array antenna2006Conference paper (Refereed)
    Abstract [en]

    In this paper a phased array antenna is described that is designed with the help of a genetic algorithm for scan angles out to 60° from broadside. The focus is on simplifying the manufacturing of the diagonally adjoining pixels and on numerical results for thin antennas. The effects of the corner to corner contacts are studied and results for two synthesized elements ar Test and measurement requirements on wireless devices

  • 315.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wikström, Andreas
    A single polarized triangular grid tapered-slot array antenna2009In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 57, no 9, p. 2599-2607Article in journal (Refereed)
    Abstract [en]

    A triangular grid single polarized tapered-slot array antenna for radar applications is studied. Compared with a rectangular grid an equilateral triangular grid allows a larger unit cell without any onset of grating lobes. Since single polarized tapered-slots in triangular grids support guided modes, which cause scan blindness, the increase in unit cell size is smaller than the optimal 15%. The design presented in the paper is capable of scan angles out to 60° from broadside in the E and H planes. To improve the match over the radar band a local minimum in the active reflection coefficient is positioned at the most critical scan direction, resulting in a reflection coefficient that is less than -12 dB in the X-band. To reduce the radar cross section for the cross-polarization an absorbing layer is positioned above the ground plane, which affects some of the guided modes that lead to scan blindnesses. An experimental antenna with 16×16 elements was built, and it was found that the H-plane performance for large scan angles for the finite antenna deviates more than expected from the infinite array approximation. Otherwise both mutual coupling measurements and embedded element patterns agrees well with the numerical results.

  • 316.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wikström, Andreas
    Calculations and measurements of a wide-band wide-scan tapered-slot array2007In: EMB 07 Computational Electromagnetics Methods and Applications, 2007, p. 249-256Conference paper (Refereed)
  • 317.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Design of Magnetostrictive Devices Using Dynamic Simulation1989In: Proc. Second Int. Conf. on Giant Magnetostrictive and Amporphous Alloys for Actuators and Sensors, Marbella, Spain, 1989, 1989Conference paper (Refereed)
  • 318.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Design Procedures for Optimal Use od Giant Magnetostrictive Materials in Magnetostrictive Actuator applications2002In: Proceedings of the 8th International Conference on New Actuators, ACTUATOR 2002, Bremen, Germany, 2002, p. 554-557Conference paper (Refereed)
  • 319.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Dynamic Simulation of Terfenol Rods under Transient Magnetization1989In: Proc. First Int. Conf. on Giant Magnetostrictive Alloys and their Impact on Actuator and Sensor Technology, Marbella, Spain, 1989, 1989Conference paper (Refereed)
  • 320.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Flextensional Transducers Based on Terfenol-D1992In: International Symposium on Giant Magnetostrictive Materials and their Applications, November 5-6, 1992, Tokyo, Japan, 1992Conference paper (Refereed)
  • 321.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Handbook of Giant Magnetostrictive Materials1999Book (Other academic)
  • 322.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modelling of Highly Magnetostrictive Materials1992In: International Symposium on Giant Magnetostrictive Materials and their Applications, November 5-6, 1992, Tokyo, Japan, 1992Conference paper (Refereed)
  • 323.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Multidisciplinary Modelling of Actuators Based on Magnetostriction2002In: Proceedings of 2nd IFAC Conference on Mechatronic Systems , Berkeley, California, USA, Edited by M. Tomizuka, 2002Conference paper (Refereed)
  • 324.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bergqvist, A.
    Lundberg, A.
    Measurements and modelling of 2-D magntization and magnetoelasticity in silicon iron1998In: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177Article in journal (Refereed)
  • 325.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bergqvist, A.
    Lundgren, A.
    Stillesjö, F.
    Statistical modeling of magnetic and magnetostrictive properties due to domain wall motion1999In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, ISSN 0021-8979, Vol. 85, no 8, p. 5190-5192Article in journal (Refereed)
    Abstract [en]

    Statistical mechanics is employed to derive magnetic and magnetostrictive bulk properties of soft magnetic materials dominated by domain wall motion. The material is divided into an ensemble of volumes with uniform magnetization, each one much smaller than a typical domain but much larger than one atom. The energy for such a volume element is assumed to consist of an internal energy: the interaction with the external magnetic field and a mean field interaction with the surrounding medium. The volume fractions of discrete mesoscopic magnetizations in the medium are derived from Boltzmann statistics. The bulk magnetization is the weighted average of the mesoscopic values. Magnetostriction is treated in a similar way. Calculations are compared with two-dimensional measurements on grain-oriented silicon #x2013;iron. #xa9; 1999 American Institute of Physics.

  • 326.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bergqvist, Anders
    Loss Simulations in Magnetostrictive Actuators1996In: J. Appl. Phys., Vol. 79, no 8Article in journal (Refereed)
  • 327.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Blomberg, Lars
    Brunsell, Per
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rosander, Staffan
    Electrotechnical modelling2011Other (Other academic)
  • 328.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Eriksson, Roland
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hörnfeldt, Sven
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Schönborg, Niclas
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electrotechnical Modelling and Design2011Other (Other academic)
  • 329.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Krah, Julius
    Alternative 2D Magnetization Measurement Methods for Soft Magnetic Materials2000In: Proceedings from the 6th International Workshop on 1&2 Dimensional Magnetic Measurement and Testing, Bad Gastein, Austria., 2000Conference paper (Refereed)
  • 330.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kvarnsjö, L.
    A Dependent Radially Resolved Simulation Model of Giant Magnetostrictive Materials1990In: Mechanical Modellings of New Electromagnetic Materials, p. 131-138Article in journal (Refereed)
  • 331.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Oscarsson, Mattias
    An approach to optimization the coil and magnetic circuit of magnetostrictive actuators2006In: 2nd IC-SCCE, 2006Conference paper (Refereed)
    Abstract [en]

    When designing a magnetostrictive actuator with bias permanent magnets one important problem is the dimensioning of the ingoing parts in order to achieve the required power output while keeping the losses as low as possible i.e. to maximize the electromechanical efficiency. It is also of interest to use the permanent magnets efficiently. This paper presents a technique which includes FE-methods of estimating the fringing fields in the vicinity of magnetostrictive actuators. A reasonable accurately estimation of the fringing field is an important issue when dimensioning the permanent magnets and the magnetic flux path of a magnetostrictive actuator. Furthermore, we desccribe a technique to determine the coil geometry, taking into account the leakage flux in the coil, for minimum resistive losses and sufficient magnetization of the active material.

  • 332.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Oscarsson, Mattias
    KTH, School of Biotechnology (BIO), Gene Technology.
    Key numbers in design of magnetostrictive actuators and generators2006In: Actuator 2006, 2006, p. 774-777Conference paper (Refereed)
    Abstract [en]

    In order to compare and judge magnetostrictive actuator designs with different design parameters a number of novel figures-of-merit are presented. The use of the suggested key numbers is demonstrated regarding the assessment of three different bias magnetization approaches. The features of a magnetostrictive power harvesting device, a so called VIBEL (VIBrational ELectric energy), are studied by means of the suggested key numbers. A VIBEL is built up like a magnetostrictive actuator, but converts a mechanical force excitation into electrical power.

  • 333.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Stillesjö, Fredrik
    Estimation of the intrinsic magnetomechanical response of magnetostrictive actuators by dynamic simulations1997In: J. of Alloys and Compounds, Vol. 258, p. 79-82Article in journal (Refereed)
  • 334.
    Engdahl, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Svensson, L.
    Simulation of the magnetostrictive performance of Terfenol-D in mechanical devices1988In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 63, p. 3924-3926Article in journal (Refereed)
    Abstract [en]

    A dynamic simulation model has been developed. Registered data from static measurements of the magnetostrictive strain for different magnetizations and mechanical stresses are used as numerical input. Easy examination of differences in dynamic performance between samples of different compositions and manufacturing methods is also possible due to a computer #x2010;aided input data handling system. The shape of the imposed magnetization can be a step, impulse, sinusoidal, or an arbitrary function. The mechanical load can be a prescribed force against the magnetostrictive element or an arbitrarily chosen mechanical impedance. The model has been verified against dynamic measurements in an experimental setup for sinusoidal and impulse magnetizations. Comparison between the model and the experimental data reveals that the model is a powerful tool for designing magnetomechanical devices based on giant magnetostrictive materials.

  • 335.
    Eriksson, Roland
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Papazyan, Ruslan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mugala, Gavita
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Localization of insulation degradation in medium voltage distribution cables2006In: 2006 International Conference on Industrial and Information Systems, Vols 1 and 2, NEW YORK: IEEE , 2006, p. 167-172Conference paper (Refereed)
    Abstract [en]

    The paper presents a methodology for successful localization of degraded insulation in medium voltage cables. Extensive work has been performed on development of cable models and characterization of new and degraded cable material to support the diagnostic technique. A non-destructive technique has been developed using differential Time Domain Reflecometry (TDR) measurements. The main application has been localization of water treed sections of XLPE cables where the voltage dependence of the permittivity of water treed insulation has been used as diagnostic criteria.

  • 336. Fakoukakis, F. E.
    et al.
    Empliouk, Tz.
    Kolitsidas, Christos
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ioannopoulos, G.
    Kyriacou, G. A.
    Ultra-Wideband butler matrix Fed MIMO antennas2015Conference paper (Refereed)
    Abstract [en]

    This work elaborates on the design of an Ultra-Wideband (UWB) Butler matrix fed antenna array, implementing a Multiple Input-Multiple Output (MIMO) configuration. The system aims at applications in future Long Term Evolution (LTE) and multifunctional Radar systems. Specifically, based on the results of our previous works, the research is extended towards the implementation of a MIMO beamforming scheme. Different beamforming scenarios are applied, in order to maximize system performance and minimize noise and interference. A comprehensive analysis and design procedure is presented, along with system simulation results.

  • 337. Fang, C.
    et al.
    Allen, B.
    Liu, E.
    Karadimas, P.
    Zhang, J.
    Alayon Glazunov, Andres
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tufvesson, F.
    Indoor-indoor and indoor-outdoor propagation trial results at 2.6 GHz2012In: Antennas and Propagation Conference (LAPC), 2012 Loughborough, IEEE , 2012, p. 6403064-Conference paper (Refereed)
    Abstract [en]

    This paper presents delay spread, coherence bandwidth, and angle-of-arrival statistics derived from an extensive MIMO channel measurement campaign carried out at a central frequency of 2.6GHz. The measurement scenarios include indoor-indoor, indoor-outdoor and indoor-outdoor-indoor. The results are useful for analytical and performance studies of post-3G wireless communication systems such as femtocell design and deployment.

  • 338. Fang, Y. T.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Transparent structure consisting of metamaterial layers and matching layers2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 2Article in journal (Refereed)
    Abstract [en]

    transparent periodic structure consisting of metamaterial (double negative) layers and matching (single negative material) layers is presented. Through the calculation of the band structure and transmission spectrum, this kind of structure is found to be omnidirectionally transparent to some electromagnetic wave of any polarization. The working frequency and bandwidth can be adjusted by changing the thicknesses of material layers.

  • 339.
    Farrag, Ahmed
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Non-contact high Voltage Measurements: FE calculations2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    It is expensive to measure potential of a high voltage transmissionline by using the ordinary ways like voltage transformers, that is whyit is very important to find a new and a cheap way to measure thispotential. A worked out 3D‐ model finite element is used to estimatecapacitance values of capacitive sensor elements of a tentative nongalvanic voltage sensor for power lines. Appropriate capacitancevalues are one essential input to the algorithm that reconstructs thepower voltages. The sensor is contactless such there is no need forhigh voltage insulation which costs a lot of money. The whole systemcan be moved easily so the measurements can be done in any pointof a line.

  • 340.
    Fazlagic, Berina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Utilization and evaluation of the Swedish incentive scheme for the regulatory period 2016-20192017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The distribution system operators in Sweden act under monopoly, whichmeans that some of its operations and functions are regulated by thegovernment authority Swedish Energy Market Inspectorate (Ei). A centralpart of Ei's task is to determine the revenue cap for all distribution systemoperators. The revenue cap is among other determined by, capital costsand quality of distributing the power.In the 2016-2019 revenue framework driving forces, in the shape of incentives,have been introduced thus to achieve efficient utilization, whereas one ofthe incentives focuses on improving the load factor. This study indicateshow the load factor can be modulated, calculated, controlled in order togenerate a more efficient use of the power grid. This implies that Ei canuse the load factor as a control / reward factor, an incentive thus to inducedistribution system operators to strive for the European Union directiveregarding efficient utilization [1].The study has been based on studying following calculation models of theload factor:1) Annual average load factor, based on daily basis.2) Weighted average, a calculation model that weight days higher with ahigh load.3) Proposed calculation model of load factor that is based on several ratiosof load factor calculations. This model is based on the average sum of:daily load factor, weekly load factor, monthly load factor, seasonal loadfactor and yearly load factor.In addition to the first part of the study, a general optimization model hasbeen developed. The optimization model has been applied to visualizehow distribution system operators can adapt their business according toincentives to achieve optimal reward.The results from the first set of the study indicate significant differences inefficiency performance and financial outcomes, depending on whichmethod of the load factor is imposed in the incentive framework. Theproposed load factor strive and require greater power of action, thus toachieve a good utilization ratio.The result of the optimization problem demonstrates a basis for assessinghow a electricity grid company can adapt its operations, such as pricepricing for different periods of time, in recognition of incentive regulation.The results indicate that price is highly dependent on how price sensitivecustomers are in demand for electricity.

  • 341. Fei, Chao
    et al.
    Zhang, Junwei
    Zhang, Guowu
    Wu, Yujian
    Hong, Xuezhi
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang Univ, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310027, Zhejiang, Peoples R China.
    Demonstration of 15-M 7.33-Gb/s 450-nm Underwater Wireless Optical Discrete Multitone Transmission Using Post Nonlinear Equalization2018In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 36, no 3, p. 728-734Article in journal (Refereed)
    Abstract [en]

    In this paper, we experimentally demonstrate an underwater wireless optical communication (UWOC) system using a 450-nm gallium nitride (GaN) laser and adaptive bit-power loading discrete multitone (DMT). To enhance the system capacity, a post nonlinear equalizer based on the simplified Volterra series is employed at the receiver to mitigate the nonlinear impairments of the UWOC system. By combining the adaptive bit-power loading with nonlinear equalization, 7.33-Gb/s DMT-modulated UWOC under 15-m tap water is achieved at a bit error rate below the 7% hard-decision forward error correction (FEC) limit 3.8 x 10(-3). The electrical signal bandwidth is 1.25 GHz, which corresponds to an electrical spectrum efficiency of similar to 6 bit/s/Hz. The capacity-distance product reaches 109.95 Gb/s-m in a single channel UWOC system with tap water. Compared with the linear equalization case, the system capacity at the FEC limit for 15-m underwater transmission is improved by similar to 18% with the nonlinear equalization. Furthermore, the impact of turbidity on the performance of UWOC system is investigated by measuring the signal-to-noise ratio (SNR) under different suspension concentrations of Al(OH)(3) and Mg(OH)(2). The results show that significant SNR gains (>3 dB for transmission distance up to 11 m) can be obtained by the nonlinear equalization over a wide range of water turbidity levels representing "clear ocean," "coastal ocean," and "harbor water," which demonstrates the robustness of the proposed scheme in various ocean environments.

  • 342.
    Feng, Wang
    et al.
    Chalmers, Div Elect Power Engn, S-41296 Gothenburg, Sweden.
    Tuan, Le
    Chalmers, Div Elect Power Engn, S-41296 Gothenburg, Sweden.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Chalmers, Div Elect Power Engn, S-41296 Gothenburg, Sweden.
    Mannikoff, Anders
    SP Technical Research Institute of Sweden, Borås 501 15, Sweden.
    Bergman, Anders
    SP Tech Res Inst Sweden, S-50115 Boras, Sweden.
    A New Approach for Benefit Evaluation of Multiterminal VSC–HVDC Using A Proposed Mixed AC/DC Optimal Power Flow2014In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, ISSN 1949-3053, Vol. 29, no 1, p. 432-443Article in journal (Refereed)
    Abstract [en]

    In this paper, an extended optimal power-flow (OPF) model incorporating a detailed model of a voltage-source con- verter-based–multiterminal high-voltage direct current system (VSC–MTDC) is proposed, hereafter referred to as the mixed ac/dc OPF (M-OPF) model. A cost-benefit analysis approach using the M-OPF model as the calculation engine is proposed to determine the preferred VSC-MTDC alternative to be installed in an existing ac transmission system. In this approach, the op- erational benefits of VSC–MTDC systems are evaluated against their investment costs to derive the benefit-to-cost ratios (BCR) which reflect the cost-effectiveness of the alternatives. A case study has been carried out using a modified Nordic 32-bus system. The results of the study show that VSC–MTDC systems might lead to a reduction in total operation cost, and the reduction of the total system transmission loss depends to a large extent on the VSC–MTDC configuration. The results from sensitivity analyses show that if the VSC loss could be reduced to a third of the original level, the total benefit from the system would be increased by about 70%. A suggestion for the placement and configuration of a VSC–MTDC system is made based on calculated BCRs. 

  • 343. Fishman, Lou
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    de Hoop, Martijn
    Time Reversal Mirrors and Cross Correlation Functions in Acoustic Wave Propagation2008In: MATHEMATICAL MODELING OF WAVE PHENOMENA, 2008, p. 183-203Conference paper (Refereed)
    Abstract [en]

    In time reversal acoustics (TRA), a signal is recorded by an array of transducers, time reversed, and then retransmitted into the configuration. The retransmitted signal propagates back through the same medium and retrofocuses on the source that generated the signal. If the transducer array is a single, planar (flat) surface, then this configuration is referred to as a planar, one-sided, time reversal mirror (TRM). In signal processing, for example, in active-source seismic interferometry, the measurement of the wave field at two distinct receivers, generated by a common source, is considered. Cross correlating these two observations and integrating the result over the sources yield the cross correlation function (CCF). Adopting the TRM experiments as the basic starting point and identifying the kinematically correct correspondences, it is established that the associated CCF signal processing constructions follow in a specific, infinite recording time limit. This perspective also provides for a natural rationale for selecting the Green's function components in the TRM and CCF expressions. For a planar, one-sided, TRM experiment and the corresponding CCF signal processing construction, in a three-dimensional homogeneous medium, the exact expressions are explicitly calculated, and the connecting limiting relationship verified. Finally, the TRM and CCF results are understood in terms of the underlying, governing, two-way wave equation, its corresponding time reversal invariance (TRI) symmetry, and the absence of TRI symmetry in the associated one-way wave equations, highlighting the role played by the evanescent modal contributions.

  • 344.
    Flache, D.
    et al.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Rakov, V. A.
    University of Florida, Gainesville, USA.
    Heidler, F. H.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Zischank, W. J.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Thottappillil, R.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the origin of two types of current pulses observed during the initial stage of upward lightning2011In: Lightning (APL), 2011 7th Asia-Pacific International Conference on, 2011, p. 235-239Conference paper (Refereed)
  • 345.
    Flache, Denis
    et al.
    Federal Armed Forces Research University, Munich, Germany.
    Rakov, Vladimir
    University of Florida, Gainesville, USA.
    Heidler, Fridolin
    Federal Armed Forces Research University, Munich, Germany.
    Zischank, Wolfgang
    Federal Armed Foprces Research University, Munich, Germany.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Different modes of charge transfer to ground in upward lightning observed at the Peissenberg tower2009Conference paper (Other academic)
    Abstract [en]

    We analyzed high-speed video images andcorresponding current records for eight upward lightningflashes initiated by the Peissenberg tower (160 m) inGermany. These flashes contained a total of 33 measurableinitial stage (IS) current pulses, which are superimposed onsteady IS currents. Seven IS pulses had relatively short (< 8μs) 10-to-90% risetimes and 26 IS pulses had relatively long(> 8 μs) risetimes. Six (86%) of seven IS current pulses withshorter risetimes each developed in a newly-illuminatedbranch, and 25 (96%) of 26 IS pulses with longer risetimesoccurred in already luminous (current-carrying) channels.These results support the hypothesis that longer risetimesare indicative of the M-component mode of charge transferto ground, while shorter risetimes are associated with theleader/return stroke mode. Similar results were obtained forM-component pulses that are superimposed on continuingcurrents following return-stroke pulses.

  • 346.
    Flache, Denis
    et al.
    Federal Armed Forces Research University, Munich, Germany.
    Rakov, Vladimir
    University of Florida, Gainesville, USA.
    Heidler, Fridolin
    Federal Armed Forces Research University, Munich, Germany.
    Zischank, Wolfgang
    Federal Armed Foprces Research University, Munich, Germany.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Leader/Return Stroke versus M-Component Mode of Charge Transfer to Ground in Initial-Stage Pulses of Upward Lightning2009Conference paper (Other academic)
  • 347.
    Forssén, Cecilia
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modelling of cavity partial discharges at variable applied frequency2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The presence of partial discharges (PD) in high voltage components is generally a sign of defects and degradation in the electrical insulation. To diagnose the condition of high voltage insulation, PD measurements is commonly used. The Variable Frequency Phase Resolved PD Analysis (VF-PRPDA) technique measures PD at variable frequency of the applied voltage. With this technique, the frequency dependence of PD can be utilized to extract more information about the insulation defects than is possible from traditional PD measurements at a single applied frequency.

    In this thesis the PD process in a disc-shaped cavity is measured and modelled at variable frequency (0.01 - 100 Hz) of the applied voltage. The aim is to interpret the PD frequency dependence in terms of physical conditions at the cavity. The measurements show that the PD process in the cavity is frequency dependent. The PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, change with the varying frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the size of the cavity and the location of the cavity (insulated or electrode bounded).

    A physical model is presented and used to dynamically simulate the sequence of PDs in the cavity at different applied frequencies. The simulations show that essential features in the measured PD patterns can be reproduced. The PD frequency dependence is interpreted as a variation in influence on the PD activity from the statistical time lag of PD and the charge transport in the cavity surface, at different applied frequencies. The simulation results also show that certain cavity parameters, like the cavity surface conductivity and the rate of electron emission from the cavity surface, change with the time between consecutive PDs, and accordingly with the applied frequency. This effect also contributes to the PD frequency dependence.

  • 348.
    Forssén, Cecilia
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Measured Applied Frequency Dependence of Partial Discharges in Disc-Shaped Cavities2007In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135Article in journal (Other academic)
  • 349.
    Forssén, Cecilia
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Partial Discharges in a Cavity at Variable Applied Frequency: Part 1: Measurements2008In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 15, no 6, p. 1601-1609Article in journal (Refereed)
    Abstract [en]

    In this paper partial discharges (PD) in disc-shaped cavities in polycarbonate are measured at variable frequency (0.01 - 100 Hz) of the applied voltage. The advantage of PD measurements at variable frequency is that more information about the insulation system may be extracted than from traditional PD measurements at a single frequency (usually 50/60 Hz). The PD activity in the cavity is seen to depend on the applied frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the cavity diameter, and the cavity location (insulated or electrode bounded). It is suggested that the PD frequency dependence is governed by the statistical time lag of PD and the surface charge decay in the cavity. This is the first of two papers addressing the frequency dependence of PD in a cavity. In the second paper a physical model of PD in a cavity at variable applied frequency is presented.

  • 350.
    Forssén, Cecilia
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Partial discharges in a cavity at variable applied frequency part 2: Measurements and modeling2008In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 15, no 6, p. 1610-1616Article in journal (Other academic)
    Abstract [en]

    In this paper partial discharges (PD) in a disc-shaped cavity are measured at variable frequency (0.01 - 100 Hz) of the applied voltage. The measured PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, changed with the varying frequency. A charge consistent model is presented and used to dynamically simulate the sequence of PDs in the cavity. The simulation results show that the properties of the cavity surface, mainly the surface conductivity and the surface emission of electrons, change with the varying applied frequency. This is interpreted as an effect of the difference in time between consecutive PDs at different applied frequencies. This is the second of two papers addressing the frequency dependence of PD in a cavity. The first paper described how the PD frequency dependence changes with the applied voltage amplitude, the cavity size and the cavity location.

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