• 대한기계학회논문집A
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• 제21권9호
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• pp.1392-1399
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• 1997

In order to determine the Mode I stress intensity factor ($K_1$) experimentally by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a ferromagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effect of the magnetic flux on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. To remove the magnetic flux, a new measuring system was made by utilizing the characteristic of coaxial transmission line. The change in potential drop in the case without magnetic flux in the air was caused by the change in electromagnetic properties near the crack tip due to magnetization. The relationship between the change in potential drop and the change in $K_I$ was linealized by demagnetization and was found to be independent of the crack length.

• 한국자기학회지
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• 제13권3호
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• pp.103-108
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• 2003

미시자기모델과 Stoner-Wohlfarth 모델을 이용하여 미크론 크기로 패터닝(patterning) 된 퍼멀로이 박막의 자기소거장 효과를 분석하였다. 또한 20 $\mu\textrm{m}$$\times$(40 $\mu\textrm{m}$~200 $\mu\textrm{m}$) 크기의 퍼멀로이 박막 시료를 DC 마그네트론 스퍼터링과 광 리소그라피(photo littlography)로 제작하였고, 제작된 시료의 자기저항 특성과 전산시늉에 의한 결과를 비교하였다. 미시자기모델에 의한 결과가 Stoner-Wohlfarth모델에 의한 결과보다 측정 데이터에 더 잘 일치하였다. 전산시늉 결과 미크론 크기로 패터닝 된 자기박막 시료의 경우 Stoner-Wohlfarth 모델에서의 자기소거장 근사식이 수정되어야함을 제안하였다.

• 한국군사과학기술학회지
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• 제14권3호
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• pp.359-363
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• 2011

An orthogonal magnetic field is often used for a military vessel in the deperm process such as Flash D deperm protocol and Anhysteretic deperm protocol. The effect of the orthogonal magnetic field on a deperm performance was investigated for a sample with strain-induced magnetization and field-induced magnetization given to different direction. A 70mm wide, 110mm long and 0.25mm thick rectangular steel plate was bent to have U-shape and to generate a strong strain on the bottom region of U-shaped steel plate. Field-induced magnetization was attached by NdFeB permanent magnet. Demagnetization was performed by applying magnetic field with a step decrement from the first field(the first shot) under the action of DC bias field.

• 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.

• 한국자기학회지
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• 제11권6호
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• pp.262-266
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• 2001

본 연구에서는 dc 마그네트론 스터링법으로 CoSm 박막을 제작하여 자기적 성질의 자성층 두께 의존성을 조사하였다. 고밀도 자기기록 매체의 여러 가지 성질 중 자기역전부피는 자기기록 매체에 저장된 정보의 열적 안정성, 자화반전기구 및 잡음을 이해하는 데 매우 중요한 자료가 된다. 따라서 자기화 감쇄의 시간 의존성과 직류 demagnetization remanence 곡선 측정결과로부터 각각 점성계수와 비가역 자화율을 구한 다음 최대 점성계수 및 비가역 자화율을 이용하여 최대 자기역전부피의 두께 의존성을 조사하였다. 자기역전부피와 보자력은 CoSm의 두께가 48 nm와 24 nm에서 각각 최대를 보이다가 오히려 감소하였으나 자기이방성은 계속 증가하는 경향을 보였다. 이와 같은 현상은 자성층의 두께가 증가함에 따라 결정립 또는 nanocrystallites 사이의 자기적 교환 상호작용이 증가하기 때문인 것으로 해석된다.

• Journal of Magnetics
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• 제16권4호
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• pp.398-402
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• 2011

A novel laminate composite of FeCuNbSiB/FeNi /PZT is proposed, where FeCuNbSiB has a permeability of around 100000, which is much larger than that of FeNi. The high-permeability FeCuNbSiB was laminated with piezomagnetic FeNi rather than attached to its ends. It is expected that the effect produced by the high permeability will act on the whole of the piezomagnetic layer. While a FeNi layer was laminated with a FeCuNbSiB layer, the strong demagnetization produced by the latter was expected to be imposed on the FeNi layer as well as the applied fields. The distribution of applied fields was altered by the high-permeability material (both bias and ac field) and the field variation positively contributed to the ME effect in piezomagnetic/piezoelectric composites. Thus the ME voltage coefficient along with the field sensitivity were improved.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권2호
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• pp.123-128
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• 2005

This paper presents an analysis of the permanent magnet overhang effect for the permanent magnetic actuator. Generally, the overhang is often used to increase the force density in permanent magnet machineries. The overhang is particularly profitable in reducing the volume after increasing the force density per volume when using the overhang effect of the permanent magnet. Therefore, the 3D Equivalent Magnetic Circuit Network Method (3D EMCN) has been used in this paper. According to the plunger position, the flux distribution per overhang length and the holding force are quantitatively compared. Furthermore, an appropriate length of the overhang has been proposed. To confirm the accuracy of the analysis method, the results of 2D FEM and 3D FEM are compared for the basic model.

• 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.

• Journal of Magnetics
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• 제20권4호
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• pp.421-426
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• 2015

This paper presents a practical method for estimation of average temperature in the permanent magnet (PM) of electric machine by using finite element analysis (FEA) and dynamo load experiment. First of all, the temperature effect of PM to the torque has been employed by FEA in order to evaluate the Temperature-Torque characteristic curve. The 1st order polynomial equation which is torque attenuation coefficient is derived by the FEA result of the Temperature-Torque curve. Next, torque saturation test with constant current condition is performed by dynamo load experiment. Then, the temperature trend can be estimated by adding the initial starting temperature using the torque attenuation coefficient and torque saturation curve. Lastly, estimated temperature is validated by infrared thermometer which measures temperature of PM surface. The comparison between the estimated result and experimental result gives a good agreement within a deviation of maximum $8^{\circ}C$.

• 전기학회논문지
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• 제64권11호
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• pp.1558-1563
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• 2015

In this paper, temperature characteristic analysis was performed by using a thermal equivalent circuit. To suppress the temperature rising, the cooling fan was installed in rotor. The temperature of permanent magnet was reduced from 66[$^{\circ}C$] to 55[$^{\circ}C$] by installing the fan. The temperature of the permanent magnets is difficult to measure. Therefore the temperature of end winding was measured directly by the thermo couple. The validity of this study was demonstrated as compared the calculated results with experimental ones.