• Journal of Magnetics
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• v.14 no.1
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• pp.42-46
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• 2009

The measurement of external magnetic field orientation using Giant Magneto Impedance (GMI) sensors has been performed. A soft magnetic alloy of $Co_{30}Fe_{34}Ni_{36}$ was electroplated on a Si wafer with a CoFeNi seed layer. V-shaped microwire patterns were formed using a conventional photolithography process. An external magnetic field was generated by a rectangular AlNiCo permanent magnet. The reference direction was defined as the external magnetic field direction oriented in the middle of 2 GMI devices. As the orientation of the magnetic field deviated from the reference direction, variation in the field component along each device introduced voltage changes. It was found that, by taking the voltage difference between the left and right arms of the Vshaped device, the nonlinearity of each device could be significantly reduced. The fabricated angle sensor had a linear range of approximately $70^{\circ}$ and an overall sensitivity of approximately 10 mV.

• Korean Journal of Materials Research
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• v.12 no.4
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• pp.279-282
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• 2002

The effect of field annealing on the velocity changes of magneto surface acoustic wave (MSAW) devices has been investigated for deposited $(Fe_{1-x}Co_x)_{89}Zr_{11}$ (x = 0~1.0) amorphous films. By means of two step field annealing at $195^{\circ}C$ for 10 minute in the magnetic field of 130 Oe, the MSAW device with x=0.4 film among the devices showed the superior velocity change of 0.1 %. This gigantic value was obtained in the DC bias field of 40 Oe at the exciting frequency of 8.7 MHz. It was confirmed that such behavior was due to the variation of differential permeability caused by an optimal stress within the magnetic film.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.3
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• pp.14-21
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• 1998

In this paper, the measurements of ELF electric and magnetic fields due to double circuit 345[kV} transmission lines are made using planar-type electric field sensor and multitum loop-type magnetic field sensor, and the magnitudes of electric and magnetic fields are illustrated by a three-dimensional plot. Also, in order to predict the magnetic field strength with lad variation, a typical daily load current curves of the transmission lines are displayed because the magnetic field is changed with load current. experimental results of ELF electric and magnetic fields along center line versus lateral distance are compared with the theoretical values computed by using the FIELDS program. The electric field intensity in and around a transmission tower is lowered, and the greatest point of the magnetic field is shifted to the heavy load line but generally is given the trend that the peak value appear at the central part of the transmission tower. The magnitudes of the maximum electric and magnetic fields in the vicinity of a transmission tower are less than 3.5[kV/m] and $20[{\mu}T]$, respectively. The measured electric and magnetic fields are satisfied with limits and guidelines recommended by various authorized international institutes.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.2
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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.

• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2783-2785
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• 2003

In multi-dimensional magnetic resonance imaging, data is obtained in the spatial frequency domain. Since the signal variation in the spatial frequency domain is much larger than that in the spatial domain, analog-to-digital converts with wide conversion bits are required. In this paper, the quantization noise in magnetic resonance imaging is analyzed. The signal-to-quantization noise ratio(SQNR) in the reconstructed image is derived from the level of quantization in the data acquisition. Since the quantization noise is proportional to the signal amplitude, it becomes more dominant in high field imaging. Using the derived formula the SQNR for several MRI systems are evaluated, and it is shown that the quantization noise can be a limiting factor in high field imaging, especially in three dimensional imaging in magnetic resonance imaging.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.41.1-41.1
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• 2010

A bipolar magnetic field perturbation in the meridional plane was observed when the Polar spacecraft crossed the plasmapause near the midnight, which was identified by a clear jump in density and temperature, from the plasmasheet to the plasmasphere. The bipolar variation shows a negative-then-positive polarity. To examine the bipolar magnetic field perturbation at the plasmapause, we assume one-dimensional model with physical quantities varying along a direction normal to the plasmapause and employ two-fluid approach for the tangential plasmapause. That is, the magnetic fields on both sides are parallel. Considering Ampere's law and pressure balance relation, we have a perturbed magnetic field, which is consistent with the observation at the plasmapause.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.790-794
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• 1995

Differential equations governing dynamic behavior of toroid-shaped ferro-magnetic material having a small gap of uniform width were derived incorporating Maxwell equations of electromagnetic induction relevent to the system and Newtonian equation of motion. Once the external uniform magnetic field was applied within the material through dc-circuit around the toroid, gap begin to change which lead to the abrupt variation of field in the material and gap according to the differential equations already derived. Characteristics of current and electromotive force with respect to time in the circuit consisting of inductance and resistance in series could be predicted from numerical solutions of these equations. As current in the circuit increasesl, magnetic field in the material increases, thus, the gap starts to shrink due to increased attractive force between gap and elastic restoring force in the material. With an appropriate selection of elastic constant of toroidal ferromagnetic material and design of gap structure it is possible to obtain the specified in both linear and nonlinear magnetic characteristics, such as current dependent and independent inductance.

• Journal of the Korean Magnetic Resonance Society
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• v.22 no.2
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• pp.40-45
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• 2018

We report Optically-Detected Magnetic Resonance (ODMR) study on Nitrogen-Vacancy (NV) centers in diamond. The experiment can easily be conducted with basic optics and microwave components. A diamond crystal having a high-density NV center is suitable for the ODMR study. The magnetic field dependence of ODMR spectrum allowed us to determine the orientation of the diamond crystal. In addition, we measured the variation of the ODMR spectrum as a function of the excitation laser power. Thermal heating induced by optical absorption caused the monotonic decrease of zero field splitting. The contrast of the ODMR peak, however, increased and, then, began to decrease, indicating the optimal laser power for recording the ODMR spectrum.

• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.32-36
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• 2007

On the contrary of a conventional motor with very narrow air-gap. it is difficult to calculate the accurate magnetic field distribution and the performance of an air-cored superconducting motor by 2 dimensional analysis. which does not use high permeability material except outer machine shield. This paper aims to do analysis of magnetic field and force distribution from the 3 dimensional modelling of a 1MW class superconducting synchronous motor. Especially. the field coil composed of Bi-2223 high-temperature superconductor and the outer machine shield are modelled by finite element analysis software according to their structures and the self-inductance and Lorentz force are calculated based on the 3 dimensional magnetic field calculation. Moreover. the influence of an important parameter, synchronous reactance, has been analyzed on the machine performances such as voltage variation and output power.

• Journal of The Korean Astronomical Society
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• v.39 no.4
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• pp.129-138
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• 2006

A period study of the semi-detached eclipsing binary system W Delphini based on the extensive series of minimum timings covering more than a century(109 years) indicates a cyclic(O-C) variation of the system. This variation can be explained as due either to (1) stellar magnetic activity cycles of the cool subgiant G5 secondary component of the binary with a subsurface magnetic field equals to 3 kG, or (2) a long-term orbital period increases with a rate of $1.68{\times}10^{-8}$ day/cycle caused by a mass transfer rate of $4.9{\times}10^{-8}M_{\odot}yr^{-1}$ from the less to more massive component modulated by a light time effect due to a hypothetical third body with period of $53.4{\pm}1.06$ years. The former explanation is more recommended than the later one since the obtained third body mass value($M_3=1.58\;M_{\odot}$) is quite large but it can not manifest itself observationally and also it cannot be a white dwarf. In the contrary, from the magnetic activity point of view, the obtained characteristics are in good consistent when applying Applegate(1992) mechanism. However, further precise photometric and CCD observations for minima timings with brightness determinations are needed to confirm the present solution.