• Journal of the Korean Magnetics Society
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• v.26 no.3
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• pp.86-91
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• 2016

The cogging torque of a brushless dc (BLDC) motor results from the interaction between permanent magnets and iron core, and it causes noise and induce vibrations. During a manufacturing process, assembly tolerances lead to the change of the electromagnetic structure of a BLDC motor where permanent magnets are not properly glued to the surface of rotor core. In this paper, the effect of magnet separation from the surface of rotor core on the cogging torque is investigated due to assembly tolerance. The relationship with key design parameters is considered such as separation between magnets and rotor core, the number of magnets having separation, as well as the several types of arrangements among neighboring magnets. Finite element method (FEM) has been used to analyze a BLDC motor, and the allowable assembly tolerance is proposed to prevent generating noise and vibrations. Within proposed assembly tolerance, it is concluded that the cogging torque of a BLDC motor is decreased, and hence noise and vibrations.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.1
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• pp.13-19
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• 2005

The performance of two designs of permanent magnet brushless motor, by having self-shielding magnetized magnets or sinusoidally shaped parallel-magnetized magnets with essentially sinusoidal airgap flux distributions, are compared. It is shown that the parallel-magnetized motor with shaped sintered NdFeB magnets can result in a higher airgap flux density and torque density than that of a self-shielding magnetized motor equipped with an anisotropic injection moulded NdFeB ring magnet.

• Journal of Aerospace System Engineering
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• v.3 no.2
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• pp.39-43
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• 2009

Eddy currents are generated when a moving conductor is exposed to a stationary magnetic field, or vice-versa. These currents create their own magnetic field, causing a repulsive force between the magnetic material and the conductor. Using this concept, a magnetic brake system can be established by the permanent magnets and a conductive material. In this paper, the eddy current effects on a magnetic brake system which consists of 2 pairs of magnets and a conductor are investigated by using a electromagnetic software, and the results of simulations are compared with experiments. It can be concluded how the arrangement of magnets effects on the dynamic characteristics of the eddy current brake system.

• Journal of Magnetics
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• v.22 no.2
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• pp.250-256
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• 2017

The article presents the principle of a relatively small device that makes it possible to generate a strong magnetic field in an air gap without electrical energy consumption. It describes the implemented design of this device, the method of the assembly of opposing linear arrays from two NdFeB magnet layers, its advantages, the possible ways of increasing the parameters further and its application in various areas.

• Archives of Metallurgy and Materials
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• v.65 no.4
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• pp.1293-1296
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• 2020

NdFeB anisotropic sintered permanent magnets are typically fabricated by strip casting or melt spinning. In this study, the plastic deformability of an NdFeB alloy was investigated to study the possibility of fabricating anisotropic sintered magnets using gas atomized powders. The results show that the stoichiometric composition Nd₁₂Fe₈₂B₆ softens at high temperatures. The aspect ratio and orientation factor of Nd₁₂Fe₈₂B₆ billets after plastic deformation were found to increase with increasing plastic deformation temperature, particularly above 800℃. This confirms that softening at high temperatures can lead to plastic deformation of Nd₂Fe₁₄B hard magnetic phases.

• Journal of Power Electronics
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• v.6 no.4
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• pp.290-297
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• 2006

Various methods have been discussed to reduce detent force in a tubular permanent magnet type linear single phase AC generator. In particular, the proposed methods depend on variations of the permanent magnet construction. These methods include two approaches in the form of sloped magnets, and conical magnets in addition to the conventional method of optimizing the magnet length. The undesired detent force ripples were calculated by a two dimensional Finite Element Method (FEM). Moreover, the generated electromotive force in the stator coils was calculated for each configuration of the permanent magnet. The experimental results agreed well with those obtained from the FEM-based simulations. Sufficient reduction in the detent force was achieved over the range of 40% while the root mean square of the output voltage was maintained. It was found that sloping the permanent magnet decreased the detent force and at the same time increased the generated rms voltage of the AC generator. The performance of the designed linear AC generator was evaluated in terms of its efficiency, total weight, losses, and power to weight ratio.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.8
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• pp.370-376
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• 2005

The single-phase induction motor is simple and durable, but the efficiency is low. Therefore, electric motors like HLDC and LSPM(line-start permanent magnet motor) that use the permanent magnet have been studied. The most advantages of single-phase LSPM is having the same stator as the stator of the single-phase induction motor and permanent magnets are just inserted in the squirrel cage rotor of the single-phase induction motor. But the characteristics of single-phase LSPM synchronous motor has very complex characteristics until the synchronization and if the design is not suitable, the single-phase LSPM synchronous motor cannot be synchronized. We designed a single-phase LSPM using the same stator and winding as the conventional single-phase induction motor, but newly designed the permanent magnets considering air gap magnetic flux density. The transient characteristics of the single-phase LSPM is not good because of a magnetic breaking torque, however, it can be improved by redesigning the rotor bars. We are proposed the design method of rotor bar for the single-phase LSPM to start softly and to make synchronization easily.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.938-948
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• 2009

In this paper, permanent magnets were used to remove magnetic sludge in the condenser of the power plant. To obtain the flow characteristics and magnetic information that are needed for determining a proper design of the magnetics sludge removal apparatus, numerical simulations were performed through the use of two commercial codes, ANSYS Workbench-Emag and CFX. Experiments were also performed on various kinds and sizes of magnets to obtain the magnetic information through a gauss meter. By analyzing the results of simulations and experiments, the minimum magnetic force that is able to remove the any size of the magnetic sludge in the condenser was calculated, and the design of the removal apparatus was confirmed. The test model which was confirmed by simulations and experiments was made. After testing, the test results were compared with those of numerical simulations and have good agreements.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.4
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• pp.225-230
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• 2004

An electromagnetic actuator has been designed and fabricated for Probe-based data storage applications. The actuator consists of permanent magnets(SmCo) housing and a media Platform which is connected to the Si frame by four couples of Si leaf springs. In order to generate electromagnetic force, Cu coils were electroplated under the media platform. The magnetic field distribution was calculated with 3D Finite Element Method of Maxwell 3D program. The field strength felt by Cu coils was estimated to be about 0.33T when the distance between the media platform and permanent magnets is $200\mu\textrm{m}$. The static and dynamic motions of the actuator were analyzed by FEM method with ANSYS 5.3. The measured displacements of the actuator were about $\pm$$92\mu\textrm{m}$ for input current of $\pm$40㎃ and the resonance frequency was 100Hz. The proposed electromagnetic actuator can be utilized for media driver of probe-based data storage system.

• Journal of Korean Medical Ki-Gong Academy
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• v.5 no.1
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• pp.22-39
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• 2001

This study is designed to compare the effect of a needle with the magnet on body. We took the skin temperature of the belly with digital infrared thermographic imaging while we sticked needle and apply magnets on L14. We made experiments on 40 healthy male volunteers for one month. We classified control group not acupuncture or magnet adhering(CON). acupuncture group on left and right L14(LA). and the permanent magnet group adhering to left and right(LM). And LM is divided into S-polar permanent magnet group(LMS) and N-polar permanent magnet group adhering to left and right L14(LMN). When we observed that temperature changed with time, the skin temperature of th belly in CON descended significantly but LM, LMS and LMN is not changed significantly. As mentioned above. we observed that the needles on L14 affected the change of temperature on the belly, and conjectured that the appliance of magnets had the same results. If the mechanism depends on the meridian of body and energy. we suppose that the appliance of magnets and needles has same effects.