• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1236-1238
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• 2003

The Earth's total magnetic field was extracted from on board TAM (Three Axis Magnetometer) observations of KOMPSAT-1 satellite between June 19th and 21st, 2000. In the pre-processing, the TAM's telemetry data were transformed from ECI (Earth Centered Inertial frame) to ECEF (Earth Centered Earth Fixed frame) and then to spherical coordination, and self-induced magnetic field by satellite bus itself were removed by using an on-orbit magnetometer data correction method. The 2-D wavenumber correlation filtering and quadrant-swapping method were applied to the pre-processed data in order to eliminate dynamic components and track-line noise, respectively. Then, the spherical harmonic coefficients are calculated from KOMPSAT-1 data. To test the validity of the TAM's geomagnetic field, Danish/NASA/French ${\phi}$rsted satellite's magnetic model and IGRF2000 model were used for statistical comparison. The correlation coefficient between ${\phi}$rsted and TAM is 0.97 and IGRF and TAM is 0.96. It was found that the data from on board magnetometer observations for attitude control of Earth-observing satellites can be used to determinate the Earth's total magnetic field and that they can be efficiently used to upgrade the global geomagnetic field coefficients, such as IGRF by providing new information at various altitudes with better temporal and spatial coverage.

• 지구물리와물리탐사
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• 제27권2호
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• pp.119-128
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• 2024

해양자력탐사는 다른 탐사법에 비해 측정이 간편하여 해저 지구조 및 광상자원 분포 등의 탐사에 개척자 탐사로 주요하게 사용되는 방법이다. 측정은 주로 해수면 견인 자력계와 선상 삼성분 자력계를 주로 사용하고 있다. 해수면 견인 자력계는 분해능이 높다는 장점이 있지만 독자적인 연구선을 사용해야 하고, 자기장의 세기 만 측정할 수 있는 반면, 선상 삼성분 자력계는 상대적으로 분해능이 낮지만 자기장의 벡터 삼성분을 측정할 수 있고 연구선을 단독으로 사용하지 않아도 자료를 획득할 수 있다는 큰 장점을 가지고 있다. 하지만, 선상 삼성분 자력계는 선박의 자성 영향으로 인해 측정된 자료의 까다로운 보정이 필요하다. 현재까지 다양한 방법론이 제시되었지만 점성자화의 영향으로부터 벡터 삼성분의 보정이 불가능하였다. 본 연구에서는 해수면 견인 총 자력계와 선상 삼성분 자력계를 동시에 획득하였을 경우, 회전행렬을 통하여 간단하게 선상 삼성분 자력계로 얻은 자료를 해수면 견인 자력계로 얻은 자료로 바꿔 줌으로써 선박의 점성자화 성분을 효과적으로 제거하여 벡터 삼성분 자력이상 자료를 근사하여 보정하는 방법을 고안하였다. 오차분석을 통해 약 7-25 nT의 오차가 발생한 것을 확인하였는데 이는 지자기 이상 벡터의 잔여성분과 이로부터 유도되는 점성자화의 영향으로 여겨진다. 이 방법은 해양지자기의 정확한 벡터성분을 제공함으로써 지자기 이상 벡터성분의 다양한 해석을 가능하게 할 뿐만 아니라, 판 이동 및 지질 구조 연구, 해양 자원 개발 등 탐사의 정확성 향상에 크게 기여할 것으로 기대된다.

• Progress in Superconductivity
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• 제1권1호
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• pp.68-72
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• 1999

Since the discovery of high Tc superconductors, great efforts have been focused to develop high performance HTS magnets for the ultimate applications to power system devices. Magnet designers, however, have had difficulties in the estimation of the maximum operating current of the designed magnet from the tested short sample data, due to the degradation of the critical current density in the magnet. Similar story applies to the HTS electrical bus bar. It has been found that the critical current of Bi-2223 stacked tapes is much less than the total summation of critical currents of each tape, which is mainly attributed to the self magnetic fields. Furthermore, since the critical current degradation of Bi-2223 tape is greater in the normal magnetic field (to the tape surface) than in the parallel one, detailed magnetic field configurations are required to reduce the self field effects. In this paper, we calculate the self field effects of a stacked conductor, defining self field factors of normal and parallel magnetic fields to the tape surface. Finally, the critical current degradations in the HTS magnet are explained by the introduced self field factors of the stacked conductor.

• 천문학회지
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• 제29권spc1호
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• pp.151-154
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• 1996

We examine the observations of large-scale magnetic fields in the Universe. We begin at the largest scale with clusters of galaxies and work our way down through galaxies and finally to the Milky Way. on which we concentrate in detail. We examine the observations of the Galactic magnetic field, and their interpretation, under the philosophy that the Galactic magnetic field is like that in other spiral galaxies. We use pulsar data. diffuse Galactic synchrotron emission, and starlight polarization data to discuss the Galaxy's global magnetic configuration and the uniform ($B_u$), random ($B_r$), and total ($B_t$) components of the field strength. We find disagreement among conclusions derived from the various data sets and argue that the pulsar data are not the best indicator for large-scale Galactic field. Near the Solar circle, we find that the azimuthal average of $B_t$ is 4.2$\mu$G and we adopt $B_u\~$2.2 and $B_r\~3.6{\mu}G$. $B_t$ is higher in spiral arms, reaching $\~5.9{\mu}G$. $B_t$ is higher for smaller $R_{Gal}$, reaching $\~8.0{\mu}G$ for $R_{Gal}$ = 4.0 kpc. The pattern of field lines is not concentric circles but spirals. The inclination of the magnetic spiral may be smaller than that of the Galaxy's spiral arms if our sample, which refers primarily to the interarm region near the Sun, is representative. However, it is not inconceivable that the local field lines follow the Galaxy's spiral pattern, as is observed in external galaxies.

• 전기학회논문지P
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• 제58권1호
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• pp.85-89
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• 2009

We investigated the quench characteristics in accordance with increase of turns number of trigger coil and shunt resistance of matrix-type superconducting fault current limiter (SFCL) with $2{\times}3$ array. The matrix-type SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit fault current. The fault current limiting characteristics according to the increase of magnetic field and applied voltage were nearly same. This is because the application of magnetic field hasn't an affect on total impedance of the SFCL. When turns number of a reactor increased, the voltage difference between two superconducting units in the current-limiting part according was decreased. The resistance difference generated in two superconducting units was also decreased. Therefore, we confirmed that the differences of the critical behaviors between superconducting units were reduced by application of magnetic field. By this results, we could decide the optimum turns number of reactor to apply magnetic field.

• 비파괴검사학회지
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• 제9권2호
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• pp.37-41
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• 1989

The purpose of this paper is to estimate the effect of wobble and nonconcentricity of tubes or rods in eddy current test with encircling test coils. Because the eddy current induced in a sample is related to the total magnetic flux linkages, the information about magnetic field distribution in a coil is important. In theoretical study, magnetic field distribution in a single turn coil was calculated and variation of impedance according to the difference of sample positions was presumed. Magnetic field intensity at inside of a solenoidal coil was measured and compared with the theoretical estimation. In experiment, impedance loci of a coil encircling an aluminum rod were measured at different sample positions. The effect of crack positions was examined at same sample positons.

• Journal of Magnetics
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• 제4권1호
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• pp.33-37
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• 1999

Unidirectional magnetic anisotropy field ($H_an$) was investigated for thin films of $CdCr{2-2x}In_{2X}Se_4 (0$\leq$x$\leq$0.2). This anisotropy originates from the microscopic anisotropic Dzyaloshinskii-Moriya (DM) interaction which arise from the spin-orbit scattering of the conduction electrons by the nonmagnetic impurities. This interaction maintains the remanent magnetization in the direction of the initial applied field. Then the single easy direction of the magnetization is parallel to the direction of the magnetic field. The anisotropy produced by field cooling is unidirectional I.e. the spins system deeps some memory of the cooling field direction. The chalcogenide spinel of$ CdCr_{2-2x}In){2X}Se_4$belongs to the class of the magnetic semiconductors. The magnetic disordered state is obtained when ferromagnetic structure is diluted by In. Then we have the mixed phase characterised by coexistence the magnetic long range ordering (IFN-infinite ferromagnetic network) and the spin glass order (Fc-finite clusters). The total magnetic anisotropy energy depends on the state of magnetic ordering. In our study we concentrated on the magnetic state with reentrant transition and spin glass state. The polycrystalline $ CdCr_{2-2x}In){2X}Se_4$ thin films were obtained by rf sputtering technique. We applied the ferromagnetic resonance (FMR) and M-H loop techniques for determining the temperature composition dependencies of Han. From the experimental data, we have found that Han decreases almost linearly when temperature is increased and in the low temperature is about three times bigger at SG state with comparison to the state with REE.

• Ocean and Polar Research
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• 제26권4호
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• pp.559-565
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• 2004

Total magnetic field measurements were performed to study paleomagnetism of three seamounts (OSM7, OSM8-1, and OSM8-2) to the northwest of the Marshall Islands in the western Pacific. The study area is located at the Ogasawara Fracture Zone which is a boundary between the Pigafetta and East Mariana basins. The magnetic parameters and paleopoles of three seamounts were derived from inversion of the measured magnetic field. The goodness-of-fit ratio of OSM7 is too low to be included to the estimation of parameters. The complex magnetic anomalies of center, scarcity of flank rift zones and steep slope at OSM7 suggest that the multiple intrusions of magma converge into the center of volcanic edifice. Inclination calculated from the magnetic anomalies of OSM8-1 and OSM8-2 is $-41.2^{\circ}$, and the paleolatitude calculated from the inclination is $23.6^{\circ}S$. The corresponding paleopoles for OSM8-1 and OSM8-2 are $(24^{\circ}42'W,\;48^{\circ}54'N)\;and\;(18^{\circ}18'W,\;48^{\circ}30'N)$, respectively. In comparison with the apparent polar wander path (APWP) of the Pacific plate, the paleopoles are close to 129-Ma pole. The paleopoles and paleolatitudes of OSM8-1 and OSM8-2 suggest that they were formed at similar time and location. The seamounts have drifted northward about $41^{\circ}$ from the paleolatitude to present latitude of seamounts.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 하계학술대회 논문집
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• pp.236-238
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• 1990

For improving magnetic properties of the amorphous Fe-B-Si alloy, we annealed in a magnetic field oriented in the plane of the ribbon longitudinal to its long axis. By field annealing, coercive force and total core loss are reduced from 0.04 Oe to 0.02 Oe, and from 0.25 watt/kg to 0.15 watt/kg respectively comparing with non-field annealed specimen. These reductions were caused by the formation of $180^{\circ}$ domains parallel to the annealing field due to the induced anisotorpy.

• Journal of Power Electronics
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• 제19권3호
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• pp.625-636
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• 2019

This paper proposes an active leakage magnetic field (LMF) suppression scheme, which uses the dual-transmitter (DT) topology, for EV wireless charging systems (EVWCS). The two transmitter coils are coplanar, concentric and driven by separate inverters. The LMF components generated by the three coils cancel each other out to reduce the total field strength. This paper gives a detailed theoretical analysis on the operating principles of the proposed scheme. Finite element analysis is used to simulate the LMF distribution patterns. Experimental results show that when there is no coil misalignment, 97% of the LMF strength can be suppressed in a 1kW prototype. These results also show that the impact on efficiency is small. The trade-off between LMF suppression and efficiency is revealed, and a control strategy to balance these two objectives is presented.