• Journal of Magnetics
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• 제18권3호
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• pp.245-249
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• 2013

A finite element model was built for MnBi/${\alpha}$-Fe nanocomposite permanent magnets, and the demagnetization curves of the magnets were simulated by micro-magnetic calculation. The microstructure of the cubic model is composed of 64 irregular grains with an average grain size of 20 nm. With the volume fraction of soft magnetic phase (t vol. %) ranged from 5 to 20 vol. %, both isotropic and anisotropic nanocomposite magnets show typical single-phase permanent magnets behavior in their demagnetization curves, illustrating good intergranular exchange coupling effect between soft and hard magnetic phases. With the increase of volume fraction of soft magnetic phase in both isotropic and anisotropic magnets, the coercive force of the magnets decreases monotonically, while the remanence rises at first to a peak value, then decreases. The optimal values of maximum energy products of isotropic and anisotropic magnets are 84 and $200kJ/m^3$, respectively. Our simulation shows that the MnBi/${\alpha}$-Fe nanocomposite permanent magnets own excellent magnetic properties and therefore good potential for practical applications.

• 한국기계가공학회지
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• 제13권5호
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• pp.70-75
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• 2014

Permanent magnets have recently been considered as device that can be used to control the behavior of mechanical systems. Neodymium magnets, a type of permanent magnet, have been used in numerous mechanical devices. These are permanent magnets made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. The magnetic selection, magnet core design and mechanical errors of the magnetic component can affect the performance of the magnetic force. In this study, the coercive force, residual induction, and the dimensions of the design parameters of the magnet core are optimized. The design parameters of magnet core are defined as the gap between the magnet and the core, the upper contact radius, and the lower thickness of the core. The force exercised on a permanent magnet in a non-uniform field is dependent on the magnetization orientation of the magnet. Non-uniformity of the polarization direction of the magnetic has been assumed to be caused by the angular error in the polarization direction. The variation in the magnetic performance is considered according to the center distance, the tilt of the magnetic components, and the polarization direction. The finite element method is used to analyze the magnetic force of an optimized cylindrical magnet.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.344-345
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• 2015

Various concentration of copper was dopped in Fe-35%Ni thin sheet by electroforming and their electromagnetic, surface properties were determined. Microstructure observation by scanning electron microscopy revealed that the thin sheet had columnar grains with about 150 nm long. Phase analysis by X-ray diffractometry revealed that the alloy thin sheets were fine crystalline. The average surface roughnesses measured by atomic force microscopy (AFM) were about 14.38 nm. Nano hardnesses determined by tribo-nano indenter were 4.13 GPa. The surface resistances were 2.28 ohm/sq. The maximum magnetization, residual magnetization and coercive force depended on the copper concentration.

• Strategy21
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• 통권30호
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• pp.236-262
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• 2012

Morgenthau claims that in international relations, there are the economic, political, and military powers that enable a nation to achieve its political and diplomatic goals. This paper explores the possibility of resolving international conflicts with naval power. First, the theoretical and historical perspective, naval power was used as a final resort to force a nation's political or diplomatic objective on an enemy nation when negotiations failed, and this was done through the physical and psychological destruction of the enemy by naval power. But as the use of military power has decreased because of the invention of the nuclear weapon, the existence of a large and capable navy deterrent has become one of the most useful military options among a nation's diplomatic measures. In other words, he focused on the political usefulness of naval power as a deterrent and coercive diplomatic tool for persuading other nations to acquiesce, rather than using naval power and actual military action as a final resort. The reason for this is that compared to army and air force, navy's flexibility, continuity, and the ability to deter are greater. The navy provides excellent accessibility through its wide mobility on the sea, and it has been shown through research that the navy possesses a political usefulness that facilitates the solution of conflicts through presence, naval intervention, and naval blockade. On the other hand, among the factors that could improve the influence of the navy are alliance relations, a reliable and powerful navy, carrots and sticks that it would have to deal with in the case of successful or unsuccessful negotiations, and support from international opinion. On this paper I introduce E.N.Luttwak's naval suasion theory. By the his theory, there are two mode of naval suasion. One is latent naval suasion the other is active suasion. Latent suasion there are deterrent mode and supportive mode. Active naval suasion there are coercive mode and supportive mode. Coercive mode has positive and negative. The limitations of naval suasion have been identified as follows. First, because the objective of the use of naval power is persuading enemy nations, the results are unpredictable. Second, the leaders of all countries possess limited understanding on the complexities of naval power and therefore lack understanding of the usefulness of naval power when choosing options. Third, in case of failure through naval suasion, prestige and reputation of a nation can be damaged. Finally, the following are additional possible research topic. First, a research on the decision making process of choosing naval power as a measure to resolve conflicts is needed. Lastly, research on the size of the navy and types of ships required for efficient naval suasion is needed. Today's world requires cooperative security regime so that middle class navy also requires political use of naval power in solving international conflicts. Therefore, additional research on this topic is needed.

• 전기학회논문지
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• 제59권4호
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• pp.715-721
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• 2010

This paper deals with the design and characteristic analysis of electro-magnet/permanent-magnet (EM-PM) hybrid levitation and propulsion device for high-speed magnetically levitated (maglev) vehicle. The machine requires PMs with high coercive force in order to levitate the vehicle by only PMs, and propulsion force is supplied by long-stator linear synchronous motor (LSM). The advantages of this configuration are an increasing levitation airgap length and decreasing total weight of the vehicle, because of the zero-power levitation control. Several design considerations such as machine structure, manufacturing, and control strategy are described. Moreover, the levitation and propulsion device for high-speed maglev vehicle has been designed and analyzed usign the electromagnetic circuit and FE analysis. In order to verify the design scheme and feasibility of maglev application, 3-DOF static force test set is implemented and tested. The obtained experimental data using the static tester shows the validity of the design and analysis approaches.

• Journal of Magnetics
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• 제13권1호
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• pp.19-22
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• 2008

ZnO nanotips, grown on c-$Al_2O_3$ and quartz, were implanted variously with 200 keV Fe or Mn ions to a dose level of $5{\times}10^{16}cm^{-2}$. The magnetic properties of these samples were measured using a superconducting quantum interference device (SQUID) magnetometer. Fe-implanted ZnO nanotips grown on c-$Al_2O_3$ showed a coercive field width of 209 Oe and a remanent field of 12% of the saturation magnetization ($2.3{\times}10^{-5}emu$) at 300K for a sample annealed at $700^{\circ}C$ for 20 minutes. The field-cooled and the zero-field-cooled magnetization measurements also showed evidence of ferromagnetism in this sample with an estimated Curie temperature of around 350 K. The Mn-implanted ZnO nanotips grown on c-$Al_2O_3$ showed superparamagnetism resulting from the dominance of a spin-glass phase. The ZnO nanotips grown on quartz and implanted with Fe or Mn showed signs of ferromagnetism, but neither was consistent.

• 열처리공학회지
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• 제10권4호
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• pp.246-254
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• 1997

The 6.5wt %Si-Fe alloy sheets were made by the twin roll process. The magnetic properties and microstructures of sheets annealed in the sulfur atmosphere were studied. In the as-prepared sheet, non-oriented columnar grains about $10{\mu}m$ in diameter were observed, which grew from the surface to the inner part of the sheet. When the annealing temperature was around $700^{\circ}C$, the primary recrystallization was formed around the middle part of the sheet thickness, and the grain size increased with increasing annealing temperature. At the annealing temperature of $900^{\circ}C$, the grain size became $30{\sim}40{\mu}m$. Around the annealing temperature, the motive force of the grain growth is the grain boundary energy. However, above $1000^{\circ}C$ the surface energy played an important role in the observed grain growth. When the sheet were annealed at $1200^{\circ}C$, the grains whose (100) planes were paralled to the thin plate surface grew, and all sheet surfaces were covered with these grains after 1 hour annealing. This phenomenon is called tertiary recrystallization. A difference in surface energy between (100) and (110) surfaces provides a driving force for growth of tertiary grains. The coercive force was 0.27 mOe and the AC core loss $W_{12/50}$ was 0.38w/kg for the 6.5wt%Si-Fe alloy.

• Journal of Advanced Marine Engineering and Technology
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• 제39권5호
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• pp.527-535
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• 2015

As a new technical approach, a hydraulic and magnetic clamp device was attempted to realize a magnetic clamp crane system that uses 8 simultaneously actuating individual hydraulic cylinders. Through this approach, a Sr type of ferritic permanent magnet ($SrO{\cdot}6Fe_2O_3$), not the previously employed electro-magnet, was utilized for the purpose of lifting and transporting the heavy weighted and oversized curved steel plates used for manufacturing the ships. This study is aimed at manufacturing and developing the hydraulic magnetic clamp prototype, which is composed of three main parts - the base frame, cylinder joint, and magnet joint - in order to safely transport such curved steel plates. Furthermore, this research was pursued to conduct a performance evaluation as to the prototype manufacture and acquire the planned quantity value and the development purpose items. The most significant item for a performance evaluation was estimated for the magnetic adhesive force (G) and in this process, a ferritic permanent magnet (Sr type) with 3700~4000 G of residual induction (Br) and 2640/2770 Oe of coercive force (Hc) was utilized. In addition, other relevant items such as hoist tension (kN), transportation time (sec), and the applied load (Kgf) exerted on the hydraulic cylinders were also evaluated in order to acquire the optimum quantity value. As a result of the evaluation, the relevant device turned out to be suitable for safely transporting the curved steel plates.

• Journal of Magnetics
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• 제2권1호
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• pp.16-21
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• 1997

Those were investigated, the crystallographic, morphological, and magnetic properties of barium ferrite film (SiO2/Si substrate) prepared by sol-gel dip coating. Appropriate sol was prepared by dissolvin barium and iron nitrate in ethylene glycol at 80$^{\circ}C$. To obtain the films, thermally oxidized p-type silicon substrate with (111) of crystallographic orientation were dipped into the sol, dried at 250$^{\circ}C$ to remove organic material, and heated at 800$^{\circ}C$ for 3 hours in air for the crystallization of barium ferrite. It was found that the particles of barium ferrite formed on the substrate exhibited needle-like shape placing parallel to the substrate and its c-axis is long axis direction. There was tendency that the coercive force in horizontal direction to the substrate was higher than that in vertical direction to it. This tendency was profound in large thickness.

• Journal of Magnetics
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• 제19권1호
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• pp.43-48
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• 2014

Magnetic materials with large coercive force and high squareness ratio are currently developing to meet an industrial demand. Since a ferromagnetic material has hysteresis characteristics, it is hard to demagnetize a ferromagnetic material precisely. In this paper, we describe deperm processes and conduct an analysis of residual magnetization of ferromagnetic material using the Preisach modeling with a two-dimensional finite elements method (FEM). From the results, it was shown that an exponential decrement form of deperm protocol is more efficient than a linear decrement form because of the demagnetizing field in the ferromagnetic material.