• 한국자기학회지
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• 제18권2호
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• pp.54-57
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• 2008

Magnetic torquer하는 인공위성의 초기 자세제어에 사용 되는 부품으로 지구자기장하에서 자기 쌍극자 모멘트가 받는 비틀림력을 이용하여 인공위성의 회전을 방지하고 특정 방향으로 인공위성의 자세가 안정되게 한다. 본 연구에서 개발 한 magnetic torque는 소형위성에 사용되는 것으로, magnetic torque거 자기적 특성뿐만 아니라 위성 발사 시 및 인공위성 궤도에서의 환경에서도 그 특성이 보장될 수 있게 환경시험을 하였다. 개발한 magnetic torquer는 포화 자기 쌍극자 모멘트가 $15Am^2$, 선형도 특성을 보이는 구간이 ${\pm}12Am^2$이고 선형도가 0.3% 미만이면서 질량이 0.46 kg이고 소비전력이 자기 쌍극자 모멘트가 $10Am^2$에 1 Watt 이였다.

• Journal of Magnetics
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• 제11권2호
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• pp.87-89
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• 2006

CoFeV thin film alloys were fabricated by electrodeposition, and the dependences of their magnetic properties on the current density were investigated using an X-ray diffractometer and a vibrating sample magnetometer. The deposited Co increased from about 45 to 60 wt.% with increasing current density until $25mA/cm^2$ whereas the deposited Fe decreased from about 55 to 40 wt.% with increasing current density until $25mA/cm^2$. The deposited V, about 2 wt.%, was independent of the current density. The current efficiencies of electrodeposition decreased linearly from about 40 to 29% with increasing current density. The X-ray diffraction measurement showed that all peaks of the CoFeV films were consistent with those of a typical Co hcp and Fe bcc mixed phase. An increase in the current density decreased the grain size and increased the lattice constant. The saturation magnetization increased from about 2.2 to 2.5 T with increasing current density. The coercivity measured in the perpendicular direction decreased from 260 to 120 Oe with increasing current density; a drastic drop of 60 Oe occurred at $5mA/cm^2$. The coercivity measured in the in-plane direction remained almost unchanged, at about 20 Oe, with increasing current density.

• Journal of Magnetics
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• 제19권1호
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• pp.1-4
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• 2014

We report the correlation between the magnetic properties and lattice parameter of $Fe_xCo_{100-x}$ alloys as a function of constituent concentration. The saturation magnetization increases with Fe content and has a maximum value at approximately x=70 at.%. However, collapse in relative saturation magnetization is observed at approximately 30 at.% to 70 at.% of Fe in $Fe_xCo_{100-x}$ alloys. The collapse is due to the formation of Co-Co and Fe-Fe antibonding states instead of Fe-Co bonds. The lattice parameter also shrinks at approximately 30 at.% to 70 at.% of Fe. This shrinkage is due to an increase in the number of nearest neighbor antisite atoms, which then leads to a decrease in the long range order parameter.

• 한국전기전자재료학회논문지
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• 제27권7호
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• pp.462-467
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• 2014

In this paper, we studied the magnetic composite sheets for electromagnetic wave noise absorber of quasi-microwave band by using soft magnetic FeSiCr and Fe50Ni flakes with the thickness of about $1{\mu}m$ and polymer. The magnetic hysteresis curve including saturation magnetization and residual magnetization and the complex permeability characteristics of the composite sheets were investigated to clarify the mixing effect on electromagnetic wave absorption properties. The saturation magnetization was decreased about 10% while the residual magnetization was increased about 15% and the real parts of complex permeability at below 500 MHz were increased 0.6~4 while those values at above 500 MHz were decreased 0.4~2.5 according to the change of contents of FeSiCr and Fe50Ni powders. As a result, the reflection loss can be moved to the lower frequency from 2~3 GHz to 1~1.5 GHz as the contents of Fe50Ni flaky powder into FeSiCr flaky powder was increased up to 50%.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2284-2291
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• 2018

This paper deals with optimum design of surface mounted permanent magnet synchronous motor (SPMSM) for automotive component. For a compact system structure, it was designed as a motor with a 14-pole 12-slot concentrated winding and hollow shaft. The motor is a thin type structure which stator outer diameter is relatively large compared to its axial length and is designed to have a high magnetic saturation for increasing the torque density. Since the high magnetic saturation in the stator core increases the axial leakage flux, a 3-dimensional (3-D) finite element analysis (FEA) is indispensable for torque analysis. However, optimum designs using 3-D FEA is inefficient in terms of time and cost. Therefore, equivalent 2-D FEA which is able to consider axial leakage flux is applied to the optimization to overcome the disadvantages of 3-D FEA. The structure for cost reduction is proposed and optimum design using equivalent 2-D FEA has been performed.

• 한국분말재료학회지
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• 제6권1호
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• pp.27-35
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• 1999

A study was made on the fabrication of nanostructured Fe-Co powders by mechanical alloying and their magnetic properties. Microstrural development during the process of MA was inverstigated by means of X-ray diffraction, differential thermal analyzer, scanning electron microscopy and transmission electron microscopy. The magnetic properties of NS Fe-Co powders were evaluated through the measurements of the saturation magnetization $(M_s)$ as well as the coercivity $(H_c)$. The average grain size calculated from line braodening in XRD peak was about 10nm or less and confirmed by TEM. In this experiment, two different milling methods (cycle opertion and conventional milling) were used. Cycle operation had an advantage over the conventional milling method in that more refined powders can be obtained. Solid state alloying of the components was confirmed from both the change of the saturation magnetization and the change of lattice parameter with Co contentration. Maxium $M_s$ was obtained at the composition of 30at.%Co. Relatively high coercivities of 10~150e were obtained for the compositions investigated, and this seems to be due to the high amount of internal strain introduced during milling.

• Journal of Magnetics
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• 제12권3호
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• pp.129-132
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• 2007

Bismuth-substituted yttrium iron garnet (Bi:YIG, $Bi_{0.5}Y_{2.5}Fe_5O_{12}$) films were deposited with aerosol deposition method and their magnetic and optical properties were investigated as a function of annealing temperature. Since the ceramic films deposited with aerosol deposition method have not a perfect crystal structure due to non-uniform internal stress occurred by mechanical collision during their deposition, the post annealing could be a key process to release its internal stress and to improve its micro structure for optimizing the magnetic and magneto-optic properties of films. The crystallinity of Bi: YIG film was improved with increase of annealing temperature, and the saturation magnetization increased up to 87 emu/cc at $800^{\circ}C$. The Faraday rotation increased up to $1.4deg/{\mu}m$ by annealing at $700^{\circ}C$ around the wavelength of $0.5{\mu}m$. The optical transmittance of the Bi:YIG film was also improved in visible region.

• Journal of Magnetics
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• 제5권4호
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• pp.111-115
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• 2000

Ultrafine $Co_{0.9}Mn_{0.1}Fe_2O_4$ powders have been fabricated by a sol-gel method. Structural and magnetic properties of the powders were investigated by x-ray diffractometry, transmission electron microscopy (TEM), Mossbauer spectroscopy, and vibrating sample magnetometry (VSM). Co-Mn ferrite powders that were fired at and above 773 K contained only a single spinel phase and behaved ferrimagnetically. Powders fired at 673 and 723 K had a spinel structure and were mixed paramagnetic and ferrimagnetic in nature. The magnetic behavior of Co-Mn ferrite powders fired at and above 873 K showed that an increase of the firing temperature yielded a decrease in the coercivity and an increase in the saturation magnetization. The maximum saturation magnetization and coercivity of Co-Mn ferrite powders were 66.7 emu/g and 1523 Oe, respectively, Mossbauer spectra of the powder fired at 923 K were taken at various temperatures ranging from 13 to 850 K. The iron ions.at both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Nel temperature $T_N$ was found to be 850 $\pm$ 2 K. Debye temperatures far A and B sites were found to be $\Theta_A = 757 \pm$5K and $Theta_B = 282 \pm$5 K, respectively.

• Journal of Magnetics
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• 제16권1호
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• pp.74-76
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• 2011

Interior permanent-magnet synchronous motors (IPMSMs) produce both magnetic and reluctance torques. The reluctance torque is due to the difference between the d- and q-axis inductances based on the geometric rotor structure. The steady-state performance analysis and precise control of the IPMSMs greatly depend on the accurate determination of the parameters. The three essential parameters of the IPMSMs are the armature flux linkage of the permanent magnet, the d-axis inductance, and the q-axis inductance. In the basic design step of an IPMSM, the inductance parameters are very important for determining the motor characteristics, such as the input voltage, torque, and efficiency. Thus, it is very important to accurately estimate the values of the motor inductances. The inductance parameters of IPMSMs have nonlinear characteristics along the magnet size because the iron core is saturated by the magnet and armature reaction fluxes. In this study, the inductance parameters were calculated using both the magnetic-equivalent-circuit method and the finite-element method (FEM). Then the calculated parameters were compensated by the saturation coefficient function, which was also calculated via the magnetic-equivalent-circuit method and FEM.

• 한국임상수의학회지
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• 제37권6호
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• pp.317-323
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• 2020

The aims of this study were to describe the appearance and size of the normal canine prostate using magnetic resonance (MR) imaging and to calculate the apparent diffusion coefficient (ADC) values. MR images were obtained from seven intact male beagle dogs using a 1.5 T MR unit. The sequences included pre- and post-contrast T1- and T2-weighted imaging with and without fat saturation. The signal intensity of the prostate was compared with the adjacent musculature, fat, and urine in the urinary bladder. We recorded the mean prostatic length, width, and height and the length of the sixth lumbar vertebral body (L6). In addition, the prostatic length (rL), width (rW), and height (rH) ratios to L6 were calculated. Diffusion-weighted images of the prostate were obtained and ADC values were calculated. The prostate was bilobed and oval-shaped, homogenous on T1-weighted images, and heterogeneous with radiating lines on T2-weighted images. Post-contrast T1-weighted sequences showed contrast enhancement of the central and radiating striations. The prostatic capsule was clearly identified on post-contrast T1-weighted images with fat saturation. The ADC values were 1.72-2.04 × 10-3mm2/sec (mean, 1.88 × 10-3mm2/sec). Knowledge of the normal appearance of the prostate on MR images is essential to assess prostatic diseases in dogs.