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  • 1.
    Abrahamsson, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ögren, Jim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 9, article id 8101809Article in journal (Refereed)
    Abstract [en]

    Brushless dc coreless electric machines with double-rotor and single-stator configuration have very low losses, since the return path of the magnetic flux rotates with the permanent magnets. The eddy-current loss in the stator is additionally very small due to the lack of iron, making it ideal for kinetic energy storage. This paper presents a design for self-bearing rotor suspension, achieved by placing the stator windings skewed on a conical surface. A mathematical analysis of the force from a skewed winding confined to the surface of a cone was found. The parametric analytical expressions of the magnitude and direction of force and torque were verified by finite-element method simulations for one specific geometry. A dynamic model using proportional-integral-differential control was implemented in MATLAB/Simulink, and the currents needed for the self-bearing effect were found by solving an underdetermined system of linear equations. External forces, calculated from acceleration measurements from a bus in urban traffic, were added to simulate the dynamic environment of an electrical vehicle.

  • 2.
    Danielsson, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Flux Distribution in Linear Permanent-Magnet Synchronous Machines Including Longitudinal End Effects2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 7, p. 3197-3201Article in journal (Refereed)
    Abstract [en]

    We investigated the longitudinal ends' influence on the flux distribution in a permanent-magnet linear synchronous machine with an analytic model and with numeric finite-element methods. We derived a general analytic expression, on closed form, from a linear reluctance model. The model reveals that the flux in a linear machine differs from that in a rotating machine in several aspects. The longitudinal ends introduce a pairwise coupled flux pattern, which will behave differently in circuits with odd or even numbers of magnets. In linear machines with an even number of magnets the pairwise coupled flux will spread throughout the whole machine, whereas in linear machines with an odd number of magnets it will be transformed into an equally distributed flux in the middle. The latter case will give rise to a nonsymmetric air gap flux distribution, where every second pole has larger flux. We confirmed the pairwise coupled flux and the nonsymmetric air gap distribution predicted by the analytic model by finite-element simulations. We noted additional effects when nonlinear behavior of the steel is taken into account. We conclude that saturation counteracts the pairwise coupled flux pattern at the longitudinal ends. Again, a nonsymmetric air gap flux distribution occurs as the pairwise coupled flux is transformed into an equally coupled flux. The pairwise coupling of the flux and the nonsymmetric air gap flux distribution give rise to a number of secondary effects, which we discuss.

  • 3. Dumas, Randy K.
    et al.
    Sani, Sohrab R.
    Mohseni, S. Majid
    Iacocca, Ezio
    Pogoryelov, Yevgen
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Muduli, Pranaba K.
    Chung, Sunjae
    Durrenfeld, Philipp
    Akerman, Johan
    Recent Advances in Nanocontact Spin-Torque Oscillators2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 6, p. 4100107-Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive review of the most recent advances in nanocontact spin torque oscillators (NC-STOs). NC-STOs are highly tunable, with both applied magnetic field and dc, broadband microwave signal generators. As opposed to the nanopillar geometry, where the lateral cross section of the entire device has been confined to a typically <100 nm diameter, in NC-STOs, it is only the current injection site that has been laterally confined on top of an extended magnetic film stack. Three distinct material combinations will be discussed: 1) a Co/Cu/NiFe pseudospin valve (PSV) where both the Co and NiFe have a dominant in-plane anisotropy; 2) a Co/Cu/[Co/Ni](4) orthogonal PSV where the Co/Ni multilayer has a strong perpendicular anisotropy; and 3) a single NiFe layer with asymmetric non-magnetic Cu leads. We explore the rich and diverse magnetodynamic modes that can be generated in these three distinct sample geometries.

  • 4. Durr, Hermann A.
    et al.
    Eimueller, Thomas
    Elmers, Hans-Joachim
    Eisebitt, Stefan
    Farle, Michael
    Kuch, Wolfgang
    Matthes, Frank
    Martins, Michael
    Mertins, Hans-Christoph
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Plucinski, Lukasz
    Schneider, Claus M.
    Wende, Heiko
    Wurth, Wilfried
    Zabel, Hartmut
    A Closer Look Into Magnetism: Opportunities With Synchrotron Radiation2009In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 45, no 1, p. 15-57Article, review/survey (Refereed)
    Abstract [en]

    The unique properties of synchrotron radiation, such as broad energy spectrum, variable light polarization, and flexible time structure, have made it an enormously powerful tool in the study of magnetic phenomena and materials. The refinement of experimental techniques has led to many new research opportunities, keeping up with the challenges put up by modern magnetism research. In this contribution, we review some of the recent developments in the application of synchrotron radiation and particularly soft X-rays to current problems in magnetism, and we discuss future perspectives.

  • 5. Ludwig, Frank
    et al.
    Kazakova, Olga
    Fernandez Barquin, Luis
    Fornara, Andrea
    Trahms, Lutz
    Steinhoff, Uwe
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Wetterskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Pankhurst, Quentin A.
    Southern, Paul
    Morales, Puerto
    Hansen, Mikkel Fougt
    Frandsen, Cathrine
    Olsson, Eva
    Gustafsson, Stefan
    Gehrke, Nicole
    Luedtke-Buzug, Kerstin
    Gruettner, Cordula
    Jonasson, Christian
    Johansson, Christer
    Magnetic, Structural, and Particle Size Analysis of Single- and Multi-Core Magnetic Nanoparticles2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 11, article id 5300204Article in journal (Refereed)
    Abstract [en]

    We have measured and analyzed three different commercial magnetic nanoparticle systems, both multi-core and single-core in nature, with the particle (core) size ranging from 20 to 100 nm. Complementary analysis methods and same characterization techniques were carried out in different labs and the results are compared with each other. The presented results primarily focus on determining the particle size-both the hydrodynamic size and the individual magnetic core size-as well as magnetic and structural properties. The used analysis methods include transmission electron microscopy, static and dynamic magnetization measurements, and Mossbauer spectroscopy. We show that particle (hydrodynamic and core) size parameters can be determined from different analysis techniques and the individual analysis results agree reasonably well. However, in order to compare size parameters precisely determined from different methods and models, it is crucial to establish standardized analysis methods and models to extract reliable parameters from the data.

  • 6.
    Lundin, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bolund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Poynting Vector Analysis of Synchronous Generators Using Field Simulations2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 9, p. 3601-3606Article in journal (Refereed)
    Abstract [en]

    The Poynting vector has been used to gain an understanding of energy flow in rotating electrical machines. Previous studies of energy flow in rotating electrical machines have used the Poynting vector in crude formulas to obtain a qualitative picture. In this paper, we present a study based on numerically calculated fields and quantities entering the Poynting vector. We obtained a detailed understanding of how energy flows in the air gap and into the winding of a synchronous generator. In particular, we found that, at no-load, energy is flowing both to and from the stator as a result of cogging, while for normal load cases the energy flow is unidirectional.

  • 7.
    Lundin, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wolfbrandt, Arne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Method for modeling time-dependent nonuniform rotor/stator configurations in electrical machines2009In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 45, no 7, p. 2976-2980Article in journal (Refereed)
    Abstract [en]

    Nonuniform air gaps in electrical machines cause problems with forces and noise. There are a number of analytical and numerical methods to calculate the response due to nonuniform air gaps. In this paper, we present an efficient method based on an effective air gap permeability. Our unified method enables all nonuniform rotor-stator configurations to be simulated. We provide some results from simulations of static and dynamic eccentricity as well as irregularity.

  • 8.
    Marcusson, Birger
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Loss Model and Finite Element Analyses of the Influence of Load Angle Oscillation on Stator Eddy Current Losses in a Synchronous Generator2017In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069Article in journal (Refereed)
    Abstract [en]

    The load angle of a synchronous generator connected to a power grid has an eigenfrequency that depends on the operating conditions. The existence of an eigenfrequency can make the generator sensitive to electrical and mechanical disturbances and motivates the use of damper windings and power stabilizing systems. The eddy current losses in the stator core and clamping structure increase as a consequence of the load angle oscillations. This is shown both with transient finite element analyses and analytically via a loss model derived from a steady state phasor model of the eddy current loss density. The model is also applicable to the quasi-steady states occurring during load angle oscillations.

  • 9.
    Marcusson, Birger
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Axial Magnetic Fields at the Ends of a Synchronous Generator at Different Points of Operation2015In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, no 2, article id 8100208Article in journal (Refereed)
    Abstract [en]

    Axial magnetic fields leaking out at the ends of a conventional rotating synchronous machine cause losses. Therefore, it is important to be able to predict the axial magnetic fields. A linear steady-state model for the axial magnetic flux density phasor in the end regions of non-salient synchronous generators has previously been verified experimentally. This paper describes an extension of the model to salient pole synchronous generators and a method for calculating the coefficients. Experiments and 3-D finite element simulations justify a distinction between axial flux density contributions from the d and q components of the stator current. How the coefficients and the axial magnetic fields in the ends of a small synchronous generator change with steady-state operation conditions is here shown with measurements and to some extent with 3-D finite element simulations.

  • 10. Mertins, Hans-Christoph
    et al.
    Legut, Dominik
    Tesch, Marc
    Jansing, Christine
    Gilbert, Markus
    Gaupp, Andreas
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Buergler, Daniel E.
    Schneider, Claus M.
    Berges, Ulf
    Detection of the Magnetocrystalline Anisotropy in X-Ray Magnetic Linear Dichroism Reflection Spectra Across the Fe 3p and 2p Edges2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 11, article id 2104704Article in journal (Refereed)
    Abstract [en]

    The magnetocrystalline anisotropy of X-ray magnetic linear dichroism (XMLD) reflection spectra measured on single-crystalline bcc Fe films across the 3p and 2p edges are presented. The XMLD spectra were obtained from a series of reflection spectra by aligning the electric field vector of linearly polarized undulator radiation with respect to the crystal axes. Our results show the presence of a huge magnetocrystalline anisotropy in the XMLD reflection spectra. The XMLD signal is further investigated as a function of the Fe film thickness in Au/Fe/Ag/GaAs layered systems. Simulations of the reflection spectra reveal the influences of interference effects, which can enhance or diminish the XMLD signals. The measured spectra are in good agreement with ab initio calculated spectra.

  • 11. Owens, Frank J.
    et al.
    Gupta, Amita
    Rao, K. V.
    Iqbal, Zafar
    Guillen, J. M. Osorio
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Guo, J. -H
    Unusual room temperature ferromagnetism in bulk sintered GaP doped with copper2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 6, p. 3043-3045Article in journal (Refereed)
    Abstract [en]

    Robust room temperature ferromagnetism is obtained in single phase Gallium Phosphide doped with Cu2+ prepared by simple solid state reaction route. The saturation magnetization at 300 K is 1.5 x 10(-2) emu/g and the coercivity was found to be 125 Oe. A strong ferromagnetic resonance signal confirms the long range magnetic order which persists to temperatures as high as 739 K. X-ray absorption spectroscopy (XAS) indicate that Cu is in a +2 state. Ab initio calculations also show that the ferromagnetic ordering is energetically favorable in Cu doped GaP. When the spin-orbit coupling is included we get an enhanced total magnetic moment of 0.31 mu(B) with a local moment on Cu 0.082 and on P 0.204 mu(B). per atom.

  • 12.
    Perers, Richard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saturation Effects on Unbalanced Magnetic Pull in a Hydroelectric Generator With an Eccentric Rotor2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 10, p. 3884-3890Article in journal (Refereed)
    Abstract [en]

    We report an investigation of saturation effects on the unbalanced magnetic pull in a hydroelectric generator with 20% static eccen-tricity. We determine the magnetic pull force by the finite-element method in parallel with a simple analytical model for various no-loadvoltages and loads. Saturation significantly affects the magnitude of the unbalanced magnetic pull for high voltages and large loads.

  • 13.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Riddar, Frida
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ericson, Fredric
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ga Implantation in a MgO-based Magnetic Tunnel Junction With Co60Fe20B20 Layers2011In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 1, p. 151-155Article in journal (Refereed)
    Abstract [en]

    A Co60Fe20B20-based tunneling magnetoresistance multilayer stack with an MgO barrier has been exposed to 30 keV Ga ions at doses corresponding to ion etching and metal deposition in a focused ion beam (FIB) instrument, to study the applicability of these processes to magnetic tunnel junction (MTJ) fabrication. MTJs were fabricated and irradiated to investigate how the exposures affected their coercivity and magnetoresistance. Elemental depth profiles, acquired using electron spectroscopy for chemical analysis, showed that Ga gathered in and around the two Co60Fe20B20 layers. Correlated with the results of the magnetic measurements, this Ga presence was found to cause a reduction of magnetoresistance and an increase in coercivity. Quantitatively, a dose of 1014 Ga+cm-2 reduced the magnetoresistance by 60%, whereas a dose of 1015 Ga+cm-2 reduced the magnetoresistance by 67% and also increased the coercivity by 2 mT and changed the dipole coupling between the sensing and the pinning layers by 1.6 mT. The latter was attributed to an imbalance in the synthetic antiferromagnetic structure, where the stack's Ru spacer served as an implantation barrier. The magnetoresistance was lost at a dose of 1016 Ga+cm-2. Annealing reduced the content of Ga around the magnetic layers but also caused diffusion of Cu from one of the layers in the stack. Apart from the observation and explanation of implantation damages in the multilayer, this work concludes on the applicability of FIB processes for prototyping of MTJs.

  • 14.
    Qejvanaj, F.
    et al.
    NanOsc AB, S-16440 Kista, Sweden.;KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Mazraati, H.
    NanOsc AB, S-16440 Kista, Sweden.;KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Jiang, S.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Sani, S. R.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Chung, S.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Magnusson, F.
    NanOsc AB, S-16440 Kista, Sweden..
    Åkerman, J.
    NanOsc AB, S-16440 Kista, Sweden.;KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Planar Hall-Effect Bridge Sensor With NiFeX (X = Cu, Ag, and Au) Sensing Layer2015In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, no 11, article id 4005404Article in journal (Refereed)
    Abstract [en]

    This paper presents a new material alloy for planar Hall-effect bridge (PHEB) sensors and the accurate analysis of the resistance and sensitivity of these materials. The sensing layer is based on NiFeX (X = Cu, Ag, and Au). These alloys have a lower resistance without a significant loss of sensitivity. The presented PHEB sensors with NiFeX sensing layer show a coercivity of 1.7 Oe, lower than that of PHEB sensors with NiFe sensing layers, which have coercivities of 2.2 Oe.

  • 15. Qejvanaj, Fatjon
    et al.
    Zubair, M.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Mohseni, S. M.
    Fallahi, V.
    Sani, S. R.
    Chung, S.
    Le, Tuan
    Magnusson, F.
    Akerman, J.
    Thick Double-Biased IrMn/NiFe/IrMn Planar Hall Effect Bridge Sensors2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 11, article id 4006104Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a new material stack for planar Hall effect bridge (PHEB) sensors and a detailed investigation of the sensitivity and noise properties of PHEB sensors made from these. The sputter deposited material stack was based on a ferromagnetic (FM) NiFe sensing layer surrounded by two layers of anti-FM IrMn. This material stack enables implementation of a thick NiFe layer without loss of sensitivity. We present an improvement in detectivity in the PHEB by changing the shape and the materials of the corners between the sensors in a meander shape. A significant reduction of noise also comes from the thick NiFe layer, due to the reduced resistance of the sensor.

  • 16.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wolfbrandt, Anna
    Lidenholm, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Core Loss Prediction in Large Hydropower Generators: Influence of Rotational Fields2009In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 45, no 8, p. 3200-3206Article in journal (Refereed)
    Abstract [en]

    In this paper, we discuss the accuracy of several core loss models as compared to experimental data obtained from measurements on commercial hydropower generators. Our aim in this paper is twofold. First, we emphasize the problem of total core loss prediction by comparing the core loss figures obtained by different loss prediction schemes with measured no-load losses. Second, we examine the predicted net effect of bidirectional flux, i.e., the rotational loss. We show that the average degree of rotation in the stator core, and hence the rotational loss, is closely related to the stator slot geometry.

  • 17.
    Sjökvist, Stefan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental Verification of a Simulation Model for Partial Demagnetization of Permanent Magnets2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 12, article id 7401105Article in journal (Refereed)
    Abstract [en]

    This article aims to verify a FEM simulation model for demagnetization of permanent magnets. The model is designed to determine the remaining magnetization within the permanent magnet after it has been exposed to high demagnetizing fields and/or temperature. An experimental setup was built and a permanent of SmCo type was experimentally tested and the results have been compared to simulation results. The results show a good agreement between results from simulationand results from experiments. A maximal deviation of 3 % of the simulation results in relation to the experimental results were achieved for most part of the magnet. During the calibration of the simulation model it was found that the coercivity had to be significantly lowered compared to the permanent magnets reference value to match simulation results to the experimental results.

  • 18. Vock, Silvia
    et al.
    Sasvari, Zoltan
    Bran, Cristina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Rhein, Fabian
    Wolff, Ulrike
    Kiselev, Nikolai S.
    Bogdanov, Alexei N.
    Schultz, Ludwig
    Hellwig, Olav
    Neu, Volker
    Quantitative Magnetic Force Microscopy Study of the Diameter Evolution of Bubble Domains in a (Co/Pd)(80) Multilayer2011In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 10, p. 2352-2355Article in journal (Refereed)
    Abstract [en]

    The evolution of bubble domains in a (Co/Pd)(80) multi-layered thin film with perpendicular anisotropy has been studied by Magnetic Force Microscopy in varying magnetic fields. As expected, the bubble domains show a continuous increase of their size with decreasing field. The diameters have been quantitatively evaluated by means of signal deconvolution. To that end the MFM tip was previously calibrated on the same multilayer in zero field state. The resulting bubble diameters and the values for bubble strip-out and collapse fields agree well with the theoretically predicted values for this system, proving the validity of the applied micromagnetic model.

  • 19.
    Wallin, Mattias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bladh, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Damper winding influence on unbalanced magnetic pull in salient pole generators with rotor eccentricity2013In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 49, no 9, p. 5158-5165Article in journal (Refereed)
    Abstract [en]

    The influence of three different damper winding configurations on unbalancedmagnetic pull (UMP) in salient pole synchronous machines with rotor eccentricity has been investigated. Continuous and noncontinuous damper windings resulted in different damperwinding currents, but their effect on the UMP was found to be very similar. Measurements of the UMP, damper bar currents, and air gap flux density were performed on a 12-pole generator witha static eccentricity under no-load conditions. Finite-element simulations of the different configurations detailing the damper winding induced flux changes are also presented.

  • 20.
    Wallin, Mattias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ranlöf, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Reduction of unbalanced magnetic pull in synchronous machines due to parallel circuits2011In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 12, p. 4827-4833Article in journal (Refereed)
    Abstract [en]

    This paper describes an analysis of the damping of unbalanced magnetic pull (UMP) in salient pole synchronous machines due to parallel stator circuits. Measurements of the UMP and currents in the parallel circuits have been performed on a 12-pole generator with the stator displaced relative to the rotor, creating a static eccentricity, and the stator winding connected as one circuit or two parallel circuits. Experiments were done at no-load conditions. Two numerical studies of the force reduction are also presented, one using a finite-element code and one using a permeance model. A good correspondence between measured and simulated forces is obtained. Results indicate that the reduction of UMP is strongly dependent on the direction of unbalance relative to the line of separation of the stator circuits. Eddy currents induced in the rotor during operation were found to reduce the standstill UMP with more than 20%.

  • 21.
    Wolfbrandt, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Automated Design of a Linear Generator for Wave Energy Converters - A Simplified Model2006In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 42, no 7, p. 1812-1819Article in journal (Refereed)
    Abstract [en]

    An encouraging way to convert ocean wave energy into electricity through direct drive is by using a linear, synchronous, longitudinal-flux permanent-magnet machine (LFM), where the piston is driven by a buoy. In this paper, the speed of the piston is assumed to be constant or sinusoidal. The paper presents an automated method for optimizing the design variables of an LFM with a rectifier, using time-stepping finite-element analysis. The method yields feasible LFM designs tailored to a given ocean wave climate, assuming constant or sinusoidal piston speed. The method will help to avoid a large amount of field calculations to obtain an optimal LFM driven by a buoy. The systematic approach results in a transparent investigation, giving the engineer an easy way to determine the best design. The paper presents LFM designs for a calm site in the Baltic Sea as examples.

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