• Journal of Sensor Science and Technology
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• v.6 no.4
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• pp.258-264
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• 1997

$YBa_{2}Cu_{3}O_{7}$ single layer dc SQUID magnetometers, prepared on $1\;cm^{2}\;SrTiO_{3}$ substrates, have been fabricated and characterized. Based on the analytical description, a SQUID magnetometer design having a 8.5 mm pickup coil with 2.6 mm linewidth, and a SQUID inductance Ls = 50 pH with $3\;{\mu}m$ Josephson junctions is presented. The devices showed a maximum modulation voltage depth of $65\;{\mu}V$ and a magnetic field noise of 0.6 pT /$\sqrt{Hz}$ at 1 Hz. Clear traces of human magnetocardiogram could be obtained with the SQUID magnetometer operating at 77 K.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.84-88
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• 2015

In this paper, we present that design and implementation of digital extreme-low-frequency (ELF) magnetic meter including wireless monitoring feature. In our lifetime, it is necessary to study how much magnetic field effects to human body. In this paper, we use 3-axis coil-type magnetic sensor, magnetic measurement range is 0.03~10uT and frequency range is 40~180Hz. As magnetic sensor characteristic, frequency loss is occurred that compensated using digital equalize based on DSP processor. Measurement value can be monitored on PC through Wifi communication and measurement error is observed within 6%.

• Journal of the Korean Magnetics Society
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• v.7 no.6
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• pp.327-333
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• 1997

We designed and constructed the high frequency magnetic characteristics measurement system to measure core loss, B-H curve, permeability of toroidal ferrite core, amorphous core and various materials for high frequency application. The system consists of universal equipments such as digitizing oscilloscope, signal generator, power amplifier, PC in order to make upgrade easily. The power source is composed of waveform synthesizer and power amplifier ranging from DC to 20 MHz, and output signal H and B from sample core are digitized by oscilloscope with sampling rate 1 GS/ s per channel. Computer controls power source and oscilloscope, reads data from oscilloscope, displays analyzed waveform and saves data with file. The entire procedures finishes within few seconds.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.84-92
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• 2001

Commercial eddy current dynamometers control the torque of rotating body, power supply machine, with the field coil current being operated as a braking force. In this paper, we studied the relation between field coil current and torque load of eddy current dynamometer. By the torque measuring analysis of eddy current dynamometer it is linear relation between the brake force measured from a torque meter which is installed at the case of dynamometer and the multiplied shaft rpm by the squares of field coil current (N$\times$I$^2$). To prove the relation, it was experimented and showed that the torque operated by the rotating body can be measured with the shaft rpm and the field coil current of the eddy current dynamometer. This result shows a possibility that eddy current dynamometer can measure the torque of rotating body without a torque measuring device. such as load cell.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.4
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• pp.51-58
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• 2008

This paper presents a new design of the precision stage for the reticle in lithography process and a low hunting control method for the stage. The stage has three axes for X, Y, ${\theta}_z$ those actuated by three voice coil motors individually. The designed reticle stage system has three gap sensors and voice coil motors, and supported by four air bearings and the forward/inverse kinematics of the stage were solved to get an accurate reference position. When a stage is in regulating control mode, there always exist small fluctuations(stage hunting) in the stage movement. Because the low stage hunting characteristic is very important in recent lithography and nano-level applications, a special regulating controller for ultra low hunting is proposed in this paper. Also this research proposed the 2-step transmission system for preventing the noise infection from environmental devices. The experimental results showed the proposed regulating control system reduced hunting noise as 35nm(rms) when a conventional PID generates 77nm(rms) in the same mechanical system. Besides the reticle stage has 100nm linear accuracy and $1{\mu}rad$ rotation accuracy at the control frequency of 8kHz.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.97-97
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• 2012

반도체 및 디스플레이 공정등에서 고진공 및 급 배기 환경을 제공하기 위하여 사용되는 터보분자펌프 (Turbomolecular Pump, TMP)는 다층의 회전깃을 갖는 로터를 회전시켜 분자를 배출시키는 방식을 사용하는 진공펌프이다. 또한 최근에는 디스플레이 및 반도체 공정에서 높은 진공도뿐만 아니라, 높은 배기속도를 요구하는 추세에 따라, 터보 펌프와 드래그 펌프부분을 동시에 가지고 있어 상대적으로 작동 진공도 영역이 넓은 복합 분자펌프(Compound Turbomolecular Pump, CMP)의 활용도가 넓어지고 있다. 이러한 분자펌프가 장시간의 고속회전에 적합하고, 베어링에서의 오염을 없앨 수 있는 비접촉 방식인 자기부상 방식이 주로 적용된다. 자기베어링 시스템은 하드웨어와 소프트웨어로 나누어질 수 있는데, 하드웨어는 회전하게 되는 블레이드 로터 및 자기베어링 로터, 모터 로터 등이 포함된 축과 고정되어 있는 자기베어링 코어와 코일, 변위센서 등의 펌프 하우징 부분, 또한 이를 제어하기 위한 전력 증폭 시스템 등의 기전적인 요소들이 이루어져 있다. 소프트웨어라 할 수 있는 제어시스템에 있어서 자기 베어링이 불안정한 특성을 갖는 개루프계를 갖고 있으므로 안정화를 위한 능동제어 시스템이 필수적이며 진동제어 등의 기능을 갖도록 적용된다. 따라서 이러한 복합분자펌프의 성능은 이러한 시스템을 구성하는 개별 요소의 성능과 이를 통합한 제어시스템의 성능이 결정한다고 할 수 있다. 본 논문에서는 현재 개발중인 2,500 l/s급의 자기부상형 고진공 복합분자펌프의 시작품에 대하여 고속회전의 안정성에 대한 연구를 수행한 내용을 보고하고 있다. 디지털 제어시스템을 적용한 시작품의 최대 26,000 rpm까지의 고속회전시의 회전 응답 및 진동 특성을 측정 분석하였으며, 로터의 고유진동수 및 진동 모우드를 분석하였다. 또한 연속 작동시의 발열특성과 각 부분의 온도와 회전 안정성과의 관계를 평가하였다.

• Progress in Superconductivity
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• v.13 no.2
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• pp.105-110
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• 2011

SQUID sensor-based ultra low-field magnetic resonance apparatus with ${\mu}T$-level measurement field requires a strong prepolarization magnetic field ($B_p$) to magnetize its sample and obtain magnetic resonance signal with a high signal-to-noise ratio. This $B_p$ needs to be ramped down very quickly so that it does not interfere with signal acquisition which must take place before the sample magnetization relaxes off. A MOSFET switch-based $B_p$ coil driver has current ramp-down time ($t_{rd}$) that increases with $B_p$ current, which makes it unsuitable for driving high-field $B_p$ coil made of superconducting material. An energy cycling-type current driver has been developed for such a coil. This driver contains a storage capacitor inside a switch in IGBT-diode bridge configuration, which can manipulate how the capacitor is connected between the $B_p$ coil and its current source. The implemented circuit with 1.2 kV-tolerant devices was capable of driving 32 A current into a thick copper-wire solenoid $B_p$ coil with a 182 mm inner diameter, 0.23 H inductance, and 5.4 mT/A magnetic field-to-current ratio. The measured trd was 7.6 ms with a 160 ${\mu}F$ storage capacitor. trd was dependent only on the inductance of the coil and the capacitance of the driver capacitor. This driver is scalable to significantly higher current of superconducting $B_p$ coils without the $t_{rd}$ becoming unacceptably long with higher $B_p$ current.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.518-525
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• 2001

As steam generator (SG) tubes have aged, new and subtle flaws have appeared. Most of them start growing from outside the tubes. Since signals from outer diameter (OD) defects are very weak compared to those from inner diameter (ID) defects in the conventional eddy current testing due to skin effect, this paper studies the feasibility of using remote field eddy current (RFEC) technique, which has shown equal sensitivity to ID and OD defects in the ferromagnetic pipe inspection. Finite element modeling studies show that the operating frequency needs to be increased up to a few hundred kHz in order for RFEC effects to occur in the nonmagnetic SG tube. The proper distance between exciter and sensor coils is also found to be about 1.5 OD, which is half the distance used in the ferromagnetic pipe inspection. Defect signals obtained by the designed RFEC probe show equal sensitivity to ID and OD defects and the existence of linear relationship between defect depth and phase signal strength. These results tell us that RFEC inspection is feasible even in nonmagnetic steam generator tubes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.6
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• pp.599-607
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• 2011

In this paper, a reaction-force compensation system for an XY linear motion stage, without an additional external isolation structure or extra motors, is developed. This system consists of a movable magnet track, a spring, a dummy weight, and a dedicated sensor module that measures the relative positions of the movable magnet track with respect to the motor coil. The reaction force compensation system is modeled, and simulations are carried out to optimize design parameters such as the moving distance of the magnet track, the transmission force, the dummy weight, and the allowed size of the mechanism. An XY linear motion stage is built, incorporating the reaction force compensation system, and the performance of the system is verified experimentally. For acceleration and deceleration values of 10 m/$s^2$, 85% of the reaction force is absorbed by the reaction force compensation system.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.89-89
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• 2011

반도체 공정 등에서 $10^{-6}{\sim}10^{-8}$ mbar의 고진공 환경을 제공하기 위하여 사용되는 고진공 터보분자펌프 (Turbomolecular Pump, TMP)는 다층의 회전깃을 갖는 로터를 회전시켜 분자를 배출시키는 방식을 사용하는 진공펌프이다. 또한 최근에는 디스플레이 및 반도체 공정에서 높은 진공도뿐만 아니라, 높은 배기속도를 요구하는 추세에 따라, 터보 펌프와 드래그 펌프부분을 동시에 가지고 있어 상대적으로 작동 진공도 영역이 넓은 복합 분자펌프(Compound Turbomolecular Pump, CMP)의 활용도가 넓어지고 있다. 이러한 분자펌프가 장시간의 고속회전에 적합하도록 비접촉 방식인 자기부상 방식의 적용이 최근 거의 표준화 되어 있다. 자기베어링 시스템은 전자기력을 이용하여 자성체인 회전축을 부상지지 함으로써 비접촉 고속 회전이 가능하여 윤활이 용이하지 않은 진공 환경 등 가혹한 환경에 적합하며, 터보분자펌프는 자기베어링이 가장 널리 사용되고 있는 분야이기도 하다. 자기베어링 시스템의 설계는 크게 하드웨어와 소프트웨어로 나누어질 수 있는데, 하드웨어의 경우 전체 로터 시스템의 특성을 고려하여 설계되어야 하며, 주로 자기베어링 코어와 코일, 변위센서 및 전력 증폭 시스템 등의 기전적인 요소들이 이루어져 있다. 하드웨어 설계와 함께 제어시스템의 설계도 매우 중요하며, 이는 자기베어링 시스템이 불안정한 특성을 갖는 개루프계를 갖고 있으므로 안정화를 위한 능동제어 시스템이 필수적이며 진동제어 등 여러 가지 기능이 요구되기 때문이다. 본 논문에서는 이러한 자기부상형 고진공 복합분자펌프의 제어를 위한 선형제어시스템의 구성을 실제 시스템의 적용을 통하여 설명하였다. 각 제어기는 DSP 를 이용한 디지털 제어시스템으로 구성되었으며, 2,500 l/s 급의 복합 분자펌프 시작품에 적용하여 25,000 rpm 까지의 기본 성능시험을 수행하였으며, 발열 특성의 개선을 위한 비선형 제어기의 설계 사례에 대한 시뮬레이션 결과를 나타내었다.