• Progress in Superconductivity
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• v.13 no.3
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• pp.151-157
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• 2012

In this paper, we used E-J constitutive law and H-formulation to calculate magnetic field profile, current density, and magnetization of high temperature superconductor (HTS) placed in time varying applied magnetic field. Finite element method (FEM)-based software, Comsol Multiphysics 3.5a, was employed to simulate 2-dimensional model of a superconducting thin strip. The numerical results based on Kim's critical state model were compared with the case of strip in a perpendicular field in the Brandt's paper as well as experimental data observed by Scanning Hall Probe and SQUID.

• Korean Journal of Acupuncture
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• v.33 no.4
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• pp.213-220
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• 2016

Objectives : The aim of this paper is to develop acupuncture needle heating system by utilizing the new method which uses high frequency(HF) time-varying magnetic field. Also, it is possible to make an assessment for reliability and clinical significance of the system. Methods : We designed the system with solenoid coils for generation of HF time-varying magnetic field that oscillates at 150 kHz. Acupuncture needles are quickly magnetized and heated by 150 kHz. We assessed clinical significance of system, such as body temperature, pressure pulse waveform. Results : Temperature of acupuncture needle increased up to 60 degree. In the result for clinical significance of system, in case of manual acupuncture stimulation(MAS), body temperature change was $0.373^{\circ}C{\pm}0.224$(p<0.05), rate of pulse energy change increased about 7.6%. In case of warm acupuncture stimulation(WAS), body temperature change was $0.645^{\circ}C{\pm}0.281$(p<0.05), rate of pulse energy change remarkably increased about 35.9%. Conclusions : We confirm that the system is able to be applied clinically to various warm acupuncture needle therapy in the area of oriental medicine.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.05a
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• pp.559-564
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• 2004

This paper deals with the device for measuring the time-varying magnetic fields and induced voltages caused by lightning discharges. The two magnetic field measuring systems were designed and made. One consists of the loop-type magnetic field sensor with the active integrator operated by a differential amplifier. The other consists of the loop-type magnetic field sensor and Labview software. The loop-type magnetic field sensor detects the time derivative of the magnetic field being measured, and the signal detected is integrated by the Labview software. As a consequence, from the calibration experiments, the frequency bandwidth of the full measuring system ranges from 400 [Hz] to 1 (MHz) and the response sensitivity are 0.98 (mV/nT) and 22 (mV/nT) for the magnetic field sensor of 2 turns and 6 turns, respectively. Also, the results obtained by the two measuring devices well agreed with each other.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.6
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• pp.1001-1009
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• 1994

The present paper deals with a new developed sensor for measuring the time-varying magnetic fields and describes the experimental results of trasient magnetic field that takes place during the operations of electric appliance. The operation principle of the self-integrating magnetic field sensor by using coaxial cable is analyzed and a calibration investigation is carried out. The frequency bandwidth of the magnetic field measurement system is from 40 Hz to about 300 kHz. The magnetic field induced by the starting and/or operation of electric appliance mainly includes the odd harmonics such as the third, the fifth and the seventh harmonics. The magnetic field intensity caused during the operation of ultrasonic washer is inversely proportional to distance, this correspodns to induction component. As a result, it was known that the odd harmonics of magnetic field in the desing of electromagnetic shield employed for protecting electronic circuit and control devices have to be considered.

• Journal of electromagnetic engineering and science
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• v.15 no.3
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• pp.134-141
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• 2015

The effect of a 60 Hz time-varying electric field was studied using a facing-electrode device (FED) and a coplanar-electrode device (CED) for further investigation of the genotoxicity of 60 Hz time-varying magnetic field (MF) from preceding research. Neither a single 30-minute exposure to the CED or to the FED had any obvious biological effects such as DNA double strand break (DSB) and apoptosis in cancerous SCC25, and HeLa cells, normal primary fibroblast IMR90 cells, while exposures of 60 Hz time-varying MF led to DNA damage with induced electric fields much smaller than those used in this experiment. Nor did repetitive exposures of three days or a continuous exposure of up to 144 hours with the CED induce any DNA damage or apoptosis in either HeLa or IMR90 cells. These results imply that the solitary electric field produced by time-varying MF is not a major cause of DSBs or apoptosis in cancer or normal cells.

• Journal of Sensor Science and Technology
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• v.4 no.2
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• pp.14-21
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• 1995

This paper deals with the active magnetic field measuring system which can measure the time-varying magnetic fields generated by power installations and lightning discharges. The magnetic field measuring system consists of the loop-type magnetic field sensor and the active integrator operated by a differential amplifier. The theoretical principle and design rule of the time-varying magnetic field measuring device and the calibration apparatus are introduced. From the calibration experiments, the frequency bandwidth of the full measuring system ranges from 270 Hz to about 2.3 MHz and the response sensitivity for magentic field strength is 128 $mV/{\mu}T$, respectively, and the calculated B-field values in the center of the loop-type sensor versus the the applied current made with a region of ${\pm}3\;%$error. The actual survey experiments by using lightning impulse current and oscillating impulse current were performed, the results of comparision between the input current waveforms and the magnetic field waveforms are a good agreement with each others and their deviations are less than 0.5 %.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.45.1-45.1
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• 2016

Spatially rotating magnetic fields have been observed in the solar wind and in the Earth's magnetopause as well as in reversed field pinch (RFP) devices. Such field configurations have a similarity with extended current layers having a spatially varying plasma pressure instead of the spatially varying guide field. It is thus expected that magnetic reconnection may take place in a rotating magnetic field no less than in an extended current layer. We have investigated the spontaneous evolution of a collisionless plasma system embedding a rotating magnetic field with a two-and-a-half-dimensional electromagnetic particle-in-cell (PIC) simulation. In magnetohydrodynamics, magnetic flux can be decreased by diffusion in O-lines. In kinetic physics, however, an asymmetry of the velocity distribution function can generate new magnetic flux near O- and X-lines, hence a dynamo effect. We have found that a magnetic-flux-reducing diffusion phase and a magnetic-flux-increasing dynamo phase are alternating with a certain period. The temperature of the system also varies with the same period, showing a similarity to sawtooth oscillations in tokamaks. We have shown that a modified theory of sawtooth oscillations can explain the periodic behavior observed in the simulation. A strong guide field distorts the current layer as was observed in laboratory experiments. This distortion is smoothed out as magnetic islands fade away by the O-line diffusion, but is soon strengthened by the growth of magnetic islands. These processes are all repeating with a fixed period. Our results suggest that a rotating magnetic field configuration continuously undergoes deformation and relaxation in a short time-scale although it might look rather steady in a long-term view.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.73-76
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• 1999

Superconductors are dissipative when exposed to time-varying magnetic fields. To analyze the AC characteristics of the superconductor, one usually needs to know magnetization curves of it. A good magnetization curves can be obtained only in a homogeneous magnetic field. In this paper, we report the fabrication and test results of a homogeneous magnet, which aims to give background magnetic fields for the superconductor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.05a
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• pp.63-66
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• 1994

This paper describes the developed sensor for measuring the time-varying magnetic fields and presents the characteristics of the magnetic fields and presents the characteristics of the magnetic field generated by lighting a fluorescent lamp. The frequency bandwidth of magnetic field measurement system is kknown as 40 Hz∼100 kHz by means of calibration experiment. The magnetic field waveform which originates from the various lighting systems was measured and the frequency components were analyzed by fast Fourier transformation technique. The magnetic field generated during the operation of the fluorescent lamp mainly includes the odd harmonics, and in the case\ulcorner of push button switch and high frequency starter types the fast transient component is occurred in an instant of lighting.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.2
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• pp.314-319
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• 2008

In this paper, the electric field distribution induced inside the brain during Transcranial Magnetic Stimulation(TMS) has been thoroughly investigated in terms of tissue heterogeneity and anisotropy as well as different head models. To achieve this, first, an elaborate head model consisting of seven major parts of the head has been built based on the Magnetic Resonance(MR) image data. Then the Finite Element Method(FEM) has been used to evaluate the electric field distribution under different head models or three different conductivity conditions when the head model has been exposed to a time varying magnetic field achieved by utilizing the Figure-Of-Eight(FOE) stimulation coil. The results show that the magnitude as well as the distribution of the induced field is significantly affected by the degree of geometrical asymmetry of head models and conductivity conditions with respect to the center of the FOE coil.