• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.337-345
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• 2000

The spontaneous Hall effect in amorphous Tb-Fe and Sm-Fe thin films, which possess excellent magnetic softness, is investigated in this work to seek a possibility of practical applications of these thin films as sensors. The resistivity of Tb-Fe thin films ranges from 180 to 250 Ωcm as the Tb content varies from 35 to 46 at. %. Tb-Fe thin films show negative Hall resistivity ranging from - 7.3 to - 5.0 Ωcm in the same composition range, giving the normalized resistivity ratio in the range of -4.1 to -2.0 %. On the other hand, the resistivity of Sm-Fe thin films ranges from 150 to 166 Ωcm as the Sm content varies from 22 to 31 at. %. Sm-Fe thin films show positive Hall resistivity which varies from 7.1 to 2.8 Ωcm in the same composition range, giving the normalized resistivity ratio in the range of 4.8 to 1.7 %. These values are significantly high compared with the values of other R-T alloys, Tb-Co alloys for example, where the highest reported value is 2.5 %. Between the two different sets of samples, Tb-Fe thin films with perpendicular anisotropy are considered to be more suitable for practical applications, since saturation is reached at a los magnetic field, approximately 2 kOe in a Tb$\sub$35.1/ Fe$\sub$64.9/ thin film, for example.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.33.3-34
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• 2008

As an activity of building Korean Space Weather Prediction Center (KSWPC), we has studied of radiation effect on the spacecraft components. High energy charged particles trapped by geomagnetic field in the region named Van Allen Belt can move to low altitude along magnetic field and threaten even low altitude spacecraft. Space Radiation can cause equipment failures and on occasions can even destroy operations of satellites in orbit. Sun sensors aboard Science and Technology Satellite (STSAT-1) was designed to detect sun light with silicon solar cells which performance was degraded during satellite operation. In this study, we try to identify which particle contribute to the solar cell degradation with ground based radiation facilities. We measured the short circuit current after bombarding electrons and protons on the solar cells same as STSAT-1 sun sensors. Also we estimated particle flux on the STSAT-1 orbit with analyzing NOAA POES particle data. Our result clearly shows STSAT-1 solar cell degradation was caused by energetic protons which energy is about 700 keV to 1.5 MeV. Our result can be applied to estimate solar cell conditions of other satellites.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.47 no.2
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• pp.1-7
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• 2010

This paper presents empirical equations indicating the high frequency performance characteristics of air-cored induction coil sensors with their constructional parameters. An air-cored induction coil sensor is widely used due to good linearity at low frequency ranges but the sensor has weakness of relatively low sensitivity to the magnetic field. At high frequency ranges, the sensitivity can be dramatically increased, largely depending on the frequency of the injected field, and this property can be a great asset to some electromagnetic inspections, since they utilize the interrogating current with a fixed frequency. The application of this property of the coil sensor requires the estimation of its high frequency performance. We made experiments on the frequency responses of the coil sensors under diverse constructional conditions and, on the basis of the experimental results, the high frequency performance, such as the resonant frequency and the sensitivity at the frequency, was estimated, as a function of the constructional parameters of the coil sensor. The good agreements between experimental and estimated data were reported.

• International Journal of Control, Automation, and Systems
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• v.1 no.2
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• pp.215-221
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• 2003

The education system in this paper is used to demonstrate and educate the effects of electromagnetic induction. Placing an aluminum ring over the core and switching on AC source causes the ring to jump in the air due to induced currents in the ring producing a magnetic field opposed to that produced in the core. To control the position of the ring by only the current, it is to require nonlinear control algorithm and control board that is composed of photo sensors, decode circuit, computer communication, and power electronics circuit. This paper provides the development for education system in detail and the effects of dynamic neural networks for nonlinear control with on line is studied.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.4
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• pp.393-399
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• 2009

Historically, industrial condition monitoring has been performed by costly hard-wired sensors or infrequent checks by maintenance personnel equipped with hand held monitoring equipment. Self- powered wireless condition monitoring systems provides on-line monitoring of critical plant and machinery providing major operating cost benefits. A vibration energy harvester(VEH) is a device that converts kinetic energy occurred by machine vibration into useable electrical energy. Using VEHs to power wireless monitoring systems can yield significant benefits: increased reliability, lower life time costs and no battery disposal issues, etc. This paper proposes the novel prototype design and manufacturing of a VEH that can eliminate the effect by failed batteries.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1169-1181
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• 1994

Vibration isolation of mechanical systems, in general, is achieved through passive or active vibration isolators. Passive vibration isolator has an inherenrt performance limitation. Whereas, active vibration isolator provides significantly superior vibration-isolation performance at the cost of energy sources and sensors. Recently, in many cases, such as suspension system, precision machinery ... etc, active isolation system outweighs its limitation. Therefore, many studies, researches, and applications are carried out in this field. In this study, vibration-isolation characteristics of an active vibration control system using electromagnetic force actuator are investigated. Several control algorithms including optimal, feedforward are used for active vibration isolation. From the experimental results of each algorithm, effective control algorithms for this active vibration-isolation system are proposed.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.241-243
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• 1999

This paper describes a series of experiments investigating the operational characteristics of high-Tc superconducting synchronous motor of five to six hundred watts capacity. In this experiment, ac 220V stator phase voltage and DC 4A excitation current are used, and the synchronous speed runs at 1800rpm. Hall Sensors are installed on the pole face and at the side of the Ag/Bi-2223 high-Tc superconducting tape in order to analyze the effect of the time-varying magnetic field on the motor performance when the load changes its value. The experimental observations are compared with the theoretical predictions.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.230-231
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• 2002

고주파전류가 통전되고 있는 연자성체에 외부자계가 인가되면 자성체의 표피효과(Skin effect)에 의해서 임피던스가 변화하게 된다. 따라서 고주파의 정전류를 통전시키면 자성체의 양단에서 전압의 크기는 외부에서 인가되는 자계에 따라 변화하게 되는데, 이 때의 전압을 자계로 환산함으로써 자계의 검출이 가능하다. 이러한 현상을 이용하여 자계를 검출하는 소자를 자기임피던스 센서(Magneto-Impedance sensor)라고 한다$^{1.2}$ . 자기임피던스 센서는 주로 연자성이 우수한 아몰퍼스 자성체를 이용하여 구성되고, 구조가 간단하며, 극히 우수한 자계 검출능력을 나타내므로, 차세대의 고감도 자계센서로서 주목을 받고 있다. (중략)

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1997.10a
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• pp.70-73
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• 1997

This paper describes the technique for detecting failure symptom of mold transformer. This study uses the vibration signal analysis method and FEM as the technique. A loading back method is constructed for experiment, accelation sensors are adhered for measurement of vibration signal. Vibration signal measured by this method is analyzed into variation trend of measurement variables by control of control variables. Magnetic field distribution of molded winding is also acquired by FEM considering the design specfication and the characteristics of insulation material, in conclusion, he relation of results between vibration signal and FEM is studied by these methods.

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.26.2-26.2
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• 2008