Contribution to laminar effects in magnetic yokes (original) (raw)
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Alternating electromagnetic field computation in laminated cores
IEEE Transactions on Magnetics, 1983
A finite element method is developed to compute alternating electromagnetic fields in laminated cores. The method is applied to a simplified model problem in order to evaluate power losses in mitered overlap joints. The influence of eddy currents on the magnetic field distribution in the neighborhood of the mitered joints is discussed, The power losses are evaluated for cores with different overlap lengths.
MAGNETIC FIELD IN MRI YOKELESS DEVICES: ANALYTICAL APPROACH
Progress In Electromagnetics Research, 2009
This paper presents a three-dimensional analytical expressions for studying the static magnetic field produced by Magnetic Resonance Imaging structures. This medical imaging technique uses a very high and uniform magnetic field produced by ring permanent magnets with rotating polarizations. However, the manufacturing of such ring permanent magnets is difficult to realize. Consequently, such ring permanent magnets are replaced by assemblies of tile permanent magnets uniformly magnetized. Unfortunately, the magnetic field produced by these tile permanent magnets uniformly magnetized is both less important and less uniform than the one produced by an idealized ring permanent magnet. We propose in this paper to study the influence of the number of tile permanent magnets used on the magnetic field properties.
Comparison of the field methods in homogenization of the laminated magnetic cores
International Journal of Applied Electromagnetics and Mechanics, 2020
The comparison of three field methods for homogenization of the laminated cores has been presented in this work. As a result, the equivalent electrical conductivity and magnetic permeability for the geometry of the core entire body were obtained for magnetic field 3D modelling. The first method is an iterative homogenization method (IHM) connected with the field solution, whereas the two others are based on analytical expressions arising from the Maxwell's equations. For 3D field solution, Finite Element numerical model including eddy currents under various frequency values was used in IHM. The model is based on a combination of the total and the reduced magnetic potentials. For comparison to our IHM, the two analytical approaches for core homogenization were used, as well. To calculate the stray losses in the homogenized laminated C-core these three approaches have been executed, as a case study. Applying suitable simplifications, according the methods of analytical homogenization, between the analytically calculated and measured values of the core losses high differences have been obtained. For the cores from amorphous strip, the analytical methods are inappropriate and our method, though iteratively implicit, gives significantly better equivalent parameters for the laminated C-core.
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IEEE Transactions on Magnetics, 1989
This paper presents a method for compensating for nonunifonnity of magnetization in a yokeless permanent magnet designed for clinical applications of nuclear magnetic resonance (NMR). The field generated by the magnet is confined within the magnetic material without the use of an external yoke. The method involves two steps: compensation in the individual magnet components and shiiruning of the assembled magnet. This paper discusses the first step, and, in particular, the compensation of the lowest hannonics of the field.
A Perturbative Method for Calculating the Impedance of Coils on Laminated Ferromagnetic Cores
A new set of formulas for calculating the self and mutual impedances of coils on straight and closed laminated ferromagnetic cores of circular cross-section has been derived. The obtained formulas generalize the well-known formulas for impedances of coils on homogeneous ferromagnetic cores, for the case of laminated cores, and improve the previously known formulas for laminated cores. The obtained formulas are fully consistent with Maxwell's equations and, therefore, offer an excellent accuracy. The perturbation theory and the average field technique are used to solve Maxwell's equations inside and outside the core. The solution inside the core can also be used in the analysis of thermal effects occurring inside the laminated core.
Effect of Geometrical Factors on Magnetic
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Eastern-European Journal of Enterprise Technologies, 2021
This paper reports the results of calculating the magnetic parameters for a direct dipole magnet in the system of vertical convergence-separation of particle beams of the upper and lower rings of the heavy-ion collider. An optimized variant of the yoke and superconducting winding structures has been obtained, providing for the assigned value of a homogeneous magnetic field inside the aperture at the minimized contributions of higher-order harmonics, average-integral along the length. The results from the analysis of the transverse projections of the magnetic induction obtained by 2D modeling of two variants of the design of the central cross-section of the dipole electromagnet are presented. The analysis results have established the dependence of the stability of magnetic parameters in the aperture of the electromagnet when the current in the winding changes on the volume of those yoke regions whose magnetization value is close to saturation. A 3D model of the magnetically active pa...
Effect of Laminated Core Body Size on Motor Magnetic Properties
Magnetism
The magnetic characteristics of electromagnetic steel sheets used for motors are evaluated under ideal sinusoidal excitation. However, in actual equipment driving, excitation by pulse-width modulation (PWM) waves is the mainstream method. Therefore, it is necessary to clarify how the magnetic properties used in motors are changed by sinusoidal excitation and inverter excitation. To clarify the magnetic properties of the laminated core by inverter excitation, samples with different core sizes were prepared and the effects on the magnetic properties were then investigated. The magnetic properties were measured by changing only the input voltage VDC while maintaining the carrier frequency and modulation factor constant. As the results, the iron loss values of the small, medium, and large samples with inverter excitation were 6.05, 9.58, and 11.62 W/kg, respectively. The iron losses of the small, medium, and large toroidal cores with inverter excitation increased by 124.9, 256.1, and 33...
A new support structure for high field magnets
IEEE Transactions on Appiled Superconductivity, 2002
Pre-stress of superconducting magnets can be applied directly through the magnet yoke structure. We have replaced the collar functionality in our 14 Tesla R&D Nb 3 Sn dipole magnets with an assembly procedure based on an aluminum shell and bladders. Bladders, placed between the coil pack and surrounding yoke inside the shell, are pressurized up to 10 ksi [70 MPa] to create an interference gap. Keys placed into the interference gap replace the bladder functionality. Following the assembly, the bladders are deflated and removed. Strain gauges mounted directly on the shell are used to monitor the stress of the entire magnet structure, thereby providing a high degree of pre-stress control without the need for high tolerances. During assembly, a force of 8.2x10 5 lbs/ft [12 MN/m] is generated by the bladders and the stress in the 1.57" [40mm] aluminum shell reaches 20.3 ksi [140 MPa]. During cool-down the thermal expansion difference between shell and yoke generates an additional compressive force of 6.85x10 5 lbs/ft [10 MN/m], corresponding to a final stress in the shell of 39.2 ksi [270 MPa]. Pre-stress conditions are sufficient for 16 T before the coils separate at the bore. Bladders have now been used in the assembly and disassembly of two 14 T magnets. This paper describes the magnet structure, assembly procedure and test results.