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Magnetisation reversal in exchange biased spin-valvesGoodman, Andrew M. January 1999 (has links)
No description available.
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Snímače proudu / Current sensorsVaculík, Vlastimil January 2012 (has links)
This diploma theisis deals with the theoretical analysis of the known types of current sensors, including for example, current transformers, shunts, and advanced sensors using Hall sensor or Rogowski coil. Subsequently, the rest of the work deals with the issue of current transducers with Hall sensors, without using a ferromagnetic circuit. For optimal currnet measure and overall precision, several possible options are designed and calculated. This includes number of sensing elements and distribution of sensors around the wires. Based on calaculation of magnetic intensity, related 3D charts ale plotted unsing Excel software. These charts illustrate the theoretical calculations of field distribution around conductors for various number of sensor. In the last part, components ale designed for practical implementation and scheme of electrical wiring. According to this scheme there is PCB designed as well. Whole current meter ir practically build and its results are compared with theoretical assumtions that are discussed in conclusion part of this theisis.
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Vórtices magnéticos em materiais nanoestruturados: experimento e simulaçãoSofia de Oliveira Parreiras 01 March 2012 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo de discos magnéticos com a configuração de vórtices magnéticos tem atraído grande interesse científico recentemente. Nessa estrutura os spins formam circuitos fechados no plano e, próximo ao centro do disco, se alinham perpendicularmente ao plano de forma a reduzir a densidade de energia de troca. O grande potencial de aplicação de vórtices magnéticos como, por exemplo, em memórias magnéticas e nanopartículas para o tratamento de câncer, chama a atenção para a investigação das condições de estabilidade e o controle de suas propriedades. Neste trabalho, estudamos a alteração que dois tipos diferentes de anisotropia provocam nas propriedades de vórtices através de medidas de Microscopia de Força Magnética (MFM) e simulações micromagnéticas utilizando o código OOMMF (NIST) que aplica a equação de Landau-Lifshitz-Gilbert para simular a configuração de spin e calcular a energia e a magnetização de microestruturas.
A primeira parte do trabalho envolveu o estudo da influência da anisotropia magnetocristalina planar na estabilidade de vórtices magnéticos em discos de Co60Fe40 em relação a discos de permalloy, que possui anisotropia magnetocristalina nula. Os resultados de simulação micromagnética para discos com diâmetros entre 0,5 e 8 m mostraram que a anisotropia favorece o alinhamento dos spins e a divisão da estrutura em domínios, reduzindo a estabilidade do vórtice. Os resultados foram comprovados experimentalmente em medidas de MFM de discos de Co60Fe40 com diâmetros entre 2 e 8 m.
Na segunda parte do trabalho foi estudada a influência do fenômeno de exchange bias na dinâmica de vórtices magnéticos. Para isso foram realizadas simulações de discos de Permalloy/Fe50Mn50 com diâmetro de 0,5 m variando o acoplamento magnético entre as camadas. As simulações de curvas de histerese mostraram que o acoplamento aumenta a estabilidade dos vórtices. Nas simulações de relaxação foi observado que devido ao exchange bias o movimento girotrópico do núcleo apresenta uma frequência variável que aumenta com o tempo, o que não acontece na ausência de exchange bias. Já nas simulações em que os discos estão sujeitos a um campo magnético girante foi observado que a velocidade crítica em que a polaridade do vórtice é invertida aumenta com o aumento do acoplamento e com o aumento da frequência do campo. Essa velocidade pode ser escolhida em uma ampla faixa escolhendo os valores do acoplamento magnético e da frequência de oscilação. Portanto é possível controlar a velocidade crítica de inversão da polaridade de vórtices magnéticos através do fenômeno de exchange bias. / The study of magnetic dots with magnetic vortex spin configuration has recently attracted great scientific interest. In this structure, the spins form closed circuits in the plane of the magnetic dot and, near the center, align perpendicularly to the plane in order to reduce exchange energy density. The great potential of applications of magnetic vortices (as for example magnetic memories and nanoparticles for cancer treatment) draws attention for the investigation of the stability conditions for the vortex configuration. In the case of soft ferromagnetic materials in micron and submicron scales, small changes in shape, size and materials anisotropy can modify the energy equilibrium. In this work, we studied the change of vortex proprieties in microsized dots due to two different types of anisotropy using the code OOMMF (NIST) that applies the Landau-Lifshitz-Gilbert equation to simulate the spin configuration and compute the energy and magnetization of microstructures. These results were compared to Magnetic Force Microscopy (MFM) investigations of the magnetic configuration in microsized dots prepared by lithographic process.
In the first part, we studied by numerical simulation the influence of planar magnetocrystaline anisotropy in Co60Fe40 disks and compare to permalloy disks, material that shows zero magnetocrystalline anisotropy. The results for disks with diameters between 0.5 and 8 m showed that the anisotropy favors spins alignment and domains division, reducing vortex stability. The results for Co60Fe40 disks with diameters between 2 and 8 m were verify experimentally by MFM measurements.
In the second part, we studied the influence of exchange bias in the magnetic vortex dynamics. A series of micromagnetic simulations for Permalloy/Fe50Mn50 disks with 0.5 m of diameter was done varying the magnetic coupling constant between the layers. The hysteresis simulations showed that the vortex stability increases with the coupling constant. In relaxation simulations we observed that the gyrotropic movement has a variable frequency that increases with time, which is not observed when exchange bias is absent. Under a rotating magnetic field, the critical velocity for vortex polarity reversion increases with the coupling constant and frequency. Our results show that the critical velocity can be adjusted in a wide range by selecting the magnetic coupling constant and the oscillating frequency, i.e., it is possible to control the critical velocity for vortex polarity inversion through the exchange bias coupling.
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Design of a field-intensified interior permanent magnet synchronous machine for electric vehicle applicationPrins, Michiel Hendrik Albertus 04 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The focus of this thesis is on the optimal design and evaluation of FI-PM machines to be used
with a MG transmission drive-train for EV application.
The machines presented are optimised using a gradient-based optimisation algorithm of
the VisualDoc software together with FE software and Python scripts. Each machine is
optimised for its own objective function. The focus is to reduce expensive rare earth material.
High torque ripple issues of the optimised machines are solved by implementing a relatively
new topology where the rotor poles/barriers are made asymmetric. The asymmetric rotor
topology implemented is effective and can be used as an alternative for rotor stack skewing.
PM demagnetisation and rotor deformation studies are conducted on the optimum designed
machines to ensure that no PM demagnetisation on the surface of the PMs and critical
rotor deformation occur.
The FE performance results of the optimum designed machines are shown and discussed.
One of the optimum designed FI-PM machines is manufactured and tested in the laboratory.
The FE and measured results of the machine are compared and shows good correlation.
The saliency performance of the optimum designed machines are evaluated as it determines
its position sensorless control capability. It is shown that the saliency ratios increase
linearly with load, making it favourable for position sensorless control. It is also shown that
the asymmetric rotor topologies introduced a larger mutual inductance compared to their
symmetric counterparts, thus higher cross-coupling is present in these rotors and therefore a
higher saliency shift, which is undesirable. Two case studies are performed in order to improve
saliency performance. The objective of the first case study is to improve the saliency shift
by reducing the flux leakage paths in the rotor. The objective of the second case study is to
optimise a FI-PM machine in order to improve the saliency ratio and -shift. The results of
the two case studies are compared with the saliency performance of the other machines. / AFRIKAANSE OPSOMMING: Die fokus van hierdie tesis is op die optimale ontwerp en evaluering van veld versterking
permanente magneet masjiene vir veelvoudige-rat elektriese voertuig toepassings.
Die masjiene teenwoordig is geoptimeer met behulp van ’n helling-gebaseerde optimering
algoritme. Elke masjien is geoptimeer vir sy eie doel funksie. Die fokus is om duur seldsame
permanent magneet materiaal te verminder.
Hoë wringkrag-rimpeleffek van die optimale masjiene word opgelos deur die implementering
van ’n relatief nuwe topologie waar die rotor pole/vloedbarrière asimmetries gemaak word.
Die asimmetriese rotor topologie wat geimplementeer is, is effektief en kan dus as ’n alternatief
vir die rotor stapel skeef metode gebruik word.
Permanent magneet demagnetisering en rotor vervorming studies is ook uitgevoer op die
optimum ontwerpte masjiene om te verseker dat geen demagnetisering plaasvind nie en ook
geen kritiese rotor vervorming nie.
Die eindige-element resultate van die optimum ontwerpte masjiene word getoon en bespreek.
Een van die optimum ontwerpte veld versterking permanente magneet masjiene is
vervaardig en getoets in die laboratorium . Die eindige-element en gemete resultate van die
masjien word vergelyk en toon goeie korrelasie.
Die speek prestasie van die optimum ontwerpte masjiene word geëvalueer aangesien dit die
sensorlose posisie beheer vermoë bepaal. Daar word getoon dat die speek koëffisiënt verhoog
lineêr met vrag wat dit gunstig maak vir posisie sensorlose beheer . Daar word ook gewys dat
die asimmetriese rotor topologie ’n groter wedersydse induktansie het in vergelyking met hul
simmetriese eweknieë, dus is daar hoër kruis-koppeling teenwoordig in die rotors en dus ’n ho¨er
speek skuif, wat ongewens is. Twee gevallestudies om speek prestasie te verbeter is uitgevoer.
Die doel van die eerste gevallestudie is om die speek skuif te verbeter deur die vermindering
van die vloed lekkasie paaie in die rotor. Die doel van die tweede gevallestudie is om ’n veld
versterking permanente magneet masjiene te optimeer ten einde die speek koëffisiënt en - skuif
te verbeter. Die resultate van die twee gevallestudies word vergelyk met die speek prestasie
van die ander masjiene.
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Desenvolvimento de um focalizador magnético utilizando um arranjo periódico de ímãs permanentes para aplicaçãao em dispositivos de microondas de potênciaPERIGO, ELIO A. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:50:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:24Z (GMT). No. of bitstreams: 1
11097.pdf: 8468953 bytes, checksum: 884442a7a2e945eacad452d3697f2149 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Desenvolvimento de um focalizador magnético utilizando um arranjo periódico de ímãs permanentes para aplicaçãao em dispositivos de microondas de potênciaPERIGO, ELIO A. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:50:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:24Z (GMT). No. of bitstreams: 1
11097.pdf: 8468953 bytes, checksum: 884442a7a2e945eacad452d3697f2149 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Snímače proudu / Current SensorsVaculík, Vlastimil January 2012 (has links)
This diploma theisis deals with the theoretical analysis of the known types of current sensors, including for example, current transformers, shunts, and advanced sensors using Hall sensor or Rogowski coil. Subsequently, the rest of the work deals with the issue of current transducers with Hall sensors, without using a ferromagnetic circuit. For optimal currnet measure and overall precision, several possible options are designed and calculated. This includes number of sensing elements and distribution of sensors around the wires. Based on calaculation of magnetic intensity, related 3D charts ale plotted unsing Excel software. These charts illustrate the theoretical calculations of field distribution around conductors for various number of sensor. In the last part, components ale designed for practical implementation and scheme of electrical wiring. According to this scheme there is PCB designed as well. Whole current meter ir practically build and its results are compared with theoretical assumtions that are discussed in conclusion part of this theisis.
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Magnetic Sensor for Nondestructive Evaluation of Deteriorated Prestressing StrandWade, James David 14 June 2010 (has links)
No description available.
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Experiments with and modelling of explosively driven mangetic flux compression generatorsAppelgren, Patrik January 2008 (has links)
This thesis presents work performed on explosively driven magnetic flux compression generators. This kind of devices converts the chemically stored energy in a high explosive into electromagnetic energy in the form of a powerful current pulse. The high energy density of the high explosives makes flux compression generators attractive as compact power sources. In order to study these devices a generator was designed at FOI in the mid-90ies. Two generators remained unused and became available for this licentiate work. The thesis reports experiments with, and simulations of, the operation of the two remaining generators. The aim was to fully understand the performance of the generator design and be able to accurately simulate its behaviour. The generators were improved and fitted with various types of diagnostics to monitor the generator operation. Two experiments were performed of which the first generator was operated well below its current capability limits while the second was stressed far above its limits. Since the generator generates a rapidly increasing current, a current measurement is the most important diagnostic revealing the current amplification of the generator and its overall performance. Further it is important to measure the timing of various events in the generator. With a common time reference it is possible to combine data from different probes and extract interesting information which cannot be directly obtained with a single measurement. Two types of numerical simulations have been performed: Hydrodynamic simulations of the high explosive interaction with the armature were used to verify the measured armature dynamics. A zero-dimensional code was used to perform circuit simulations of the generator. The model takes into account the inductance reduction due to the compression of the generator as well as the change in conductivity due to heating of the conductors in the generators. / QC 20101103
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Theoretical magnetic flux emergenceMacTaggart, David January 2011 (has links)
Magnetic flux emergence is the subject of how magnetic fields from the solar interior can rise and expand into the atmosphere to produce active regions. It is the link that joins dynamics in the convection zone with dynamics in the atmosphere. In this thesis, we study many aspects of magnetic flux emergence through mathematical modelling and computer simulations. Our primary aim is to understand the key physical processes that lie behind emergence. The first chapter introduces flux emergence and the theoretical framework, magnetohydrodynamics (MHD), that describes it. In the second chapter, we discuss the numerical techniques used to solve the highly non-linear problems that arise from flux emergence. The third chapter summarizes the current literature. In the fourth chapter, we consider how changing the geometry and parameter values of the initial magnetic field can affect the dynamic evolution of the emerging magnetic field. For an initial toroidal magnetic field, it is found that its axis can emerge to the corona if the tube’s initial field strength is large enough. The fifth chapter describes how flux emergence models can produce large-scale solar eruptions. A 2.5D model of the breakout model, using only dynamic flux emergence, fails to produce any large scale eruptions. A 3D model of toroidal emergence with an overlying magnetic field does, however, produce multiple large-scale eruptions and the form of these is related to the breakout model. The sixth chapter is concerned with signatures of flux emergence and how to identify emerging twisted magnetic structures correctly. Here, a flux emergence model produces signatures found in observations. The signatures from the model, however, have different underlying physical mechanisms to the original interpretations of the observations. The thesis concludes with some final thoughts on current trends in theoretical magnetic flux emergence and possible future directions.
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