Optimization of Magnetic Field Uniformity of NMR Multiphase Flow Permanent Magnets
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Keywords:
Electropermanent magnet
Magnetostatics
Pole piece
Halbach array
Force between magnets
Electromagnet
This paper presents an analytical model of magnetic field of a permanent magnet synchronous motor (PMSM) with a trapezoidal Halbach permanent magnet array (THPMA). Compared with conventional Halbach array, the shape of each magnet in THPMA is transformed from rectangle to trapezium in polar coordinates. The THPMA is delaminated indefinitely radially and each layer is approximately considered to be a conventional Halbach array. The air-gap magnetic field of each layer is analyzed with the scalar magnetic potential. Then, the air-gap magnetic field of the THPMA is obtained by superposing magnetic fields of all layers. The validity of the analytical model is verified by a finite-element model (FEM). The air-gap flux density is optimized by adjusting the center angle coefficients of the THPMA, and a no-load phase back electromotive force (EMF) with the harmonic distortion rate (THD) of 0.75% is obtained by FEM. The back EMF is basically consistent with the measured result of a prototype motor.
Halbach array
Counter-electromotive force
Electropermanent magnet
Scalar potential
Electromotive force
Pole piece
Synchronous motor
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Halbach array is effective in forming a strong magnetic field. However, the conventional model is difficult to control the magnetic field because all the rectangular shaped permanent magnets are strongly fixed. Proposal Halbach array is constructed with cylinder shaped permanent magnets and rotating all magnets to control the magnetic field. The magnetic flux distribution of the Halbach array using cylinder shaped permanent magnets has been measured actually and simulated to provide the details on the magnetic performance of the proposal model. In the Halbach array using cylinder shaped permanent magnets, by synchronized rotation in the same direction with of all magnets, the slide of the magnetic field distribution has been confirmed. In this paper, it reveals that the features of the proposal model by comparing the detailed measurement and simulation results.
Halbach array
Electropermanent magnet
Electrodynamic suspension
Force between magnets
Pole piece
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The damping force of the magnetic damper in this paper is based on Lorentz force by Fleming's left-hand rule. That is to say, the force acts on the conductor in the opposite direction of the movement of the conducting disk. Generally, a magnetic damper has a weak point that damping performance is relatively weak. In the present work, we propose Halbach magnet array or another magnet array system to apply to the higher performance magnetic damper. In the case of Halbach magnet array, the five cubic magnets are glued in the different special direction of the magnetic pole each other. We fabricated the magnetic damper using one Halbach magnet array made of 5 ferrite magnet cubes and calculated damping ratios experimentally, and compared them with analytical results. As a result, it was found that we need to use plural Halbach magnet array or special magnet array made of neodymium magnets in order to gain the higher damping ratios.
Halbach array
Electropermanent magnet
Pole piece
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A novel 2-D permanent magnet array for a planar actuator was proposed, in which the portion between adjacent magnetic poles was divided to four small rectangular solids. Magnetic fields of the permanent magnet array were analyzed systematically by 3D finite element method. The analysis results show that, compared with the well-known Halbach magnet array, the proposed array has higher permanent magnet utilization. Keeping the whole permanent magnet volume constant, the arrays with several improved structures were put forward. The magnetic field analyze results prove that the utilization is best, when the ratio between the height of the magnetic poles magnetized vertically and the height of the portion magnetized horizontally is about 2.
Halbach array
Electropermanent magnet
Pole piece
Planar array
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In order to improve the output force characteristics of permanent magnet linear motor (PMLM), studied from permanent magnets (PMs) structure that is the key component of PMLM, different magnetization methods of single PM and different array structures of multiple PMs are compared, and a novel PMLM magnetized alone the external field force lines using 8 pieces tegular Halbach magnet array with air gaps is proposed as well. The analysis on magnetic field of PMLM shows that the force between the coil and the single PM increases by more than 40%, and the average magnetic induction in coil centre generated by the 8 pieces Halbach magnet array arrives at the maximum value, 10% higher than that of 1 piece structure.
Halbach array
Electropermanent magnet
Pole piece
Air gap (plumbing)
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Electromagnet
Halbach array
Electropermanent magnet
Dipole magnet
Pole piece
Magnetic circuit
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Halbach array
Electromagnet
Electropermanent magnet
Dipole magnet
Pole piece
Force between magnets
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The damping force of a magnetic damper is based on the Lorentz force. That is to say, the magnetic damping force is generated in the direction opposite to the relative motion of a conductor with respect to a magnet. Normally, a magnetic damper uses two conducting plates facing the opposite sides of a magnet. If only one side of the magnet is used, the magnetic damping force is less. In the present work, a new magnetic damper composed of Halbach magnet arrays arranged in three parallel lines is proposed. A basic Halbach magnet array consists of five magnet cubes that are glued in the specific directions relative to each other, and is characterized as having a strong magnetic field on one side and a weak field on the other. For this reason, it is possible to realize a high-performance magnetic damper using only one side of a magnet. The magnetic fields of the Halbach magnet arrays of the new magnetic damper we are proposing, together with other magnet arrays, were investigated analytically using Biot-Savart’s Law. Furthermore, the proposed magnetic damper was fabricated and tested. The experimental results were compared with the analytical results. As a result, the effectiveness of the new magnetic damper was confirmed.
Halbach array
Electropermanent magnet
Pole piece
Force between magnets
Electrodynamic suspension
Lorentz force
Magnetic circuit
Spin-stabilized magnetic levitation
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The mathematical model of magnetic field produced by the permanent magnet is a key problem on magnetic localization of micro-medical devices in human body.Magnetic dipoles model and equivalent magnetic monopoles model are two often used models for obtaining static magnetic field distribution.The two models were used to simulate the magnetic field of cylinder magnet used in the drug delivery capsule.The calculation results of the two models are very close when the distance between the field point and the magnet is larger as 10 times of the magnet's size.The real experiments on the experimental device approved the simulation results,which mean that the magnetic dipoles model is suitable for magnetic localization of micro-medical devices in human body when the distance between the magnet and the magnetic sensor is larger as 10 times of the magnet's size.
Force between magnets
Dipole magnet
Electropermanent magnet
Pole piece
Electrodynamic suspension
Electromagnet
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Based on the basic model of the permanent motor with the inside rotor of Halbach magnet array structure,compare Halbach magnet structure with ordinary magnetic pole of the permanent magnet motor.The air-gap flux density distribution of Halbach magnet structure has been analyzed to get the air-gap flux density of the magnet structure,changing laws of the flux with the thickness of the permanent magnet.It shows that Halbach array has characteristic of magnetic single side and fine sine characteristic.
Halbach array
Electropermanent magnet
Air gap (plumbing)
Pole piece
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