• 한국초전도ㆍ저온공학회논문지
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• 제9권2호
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• pp.7-10
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• 2007

Persistent mode HTS pancake coil has been fabricated using a coated conductor by a "wind-and-flip" method. A coated conductor with the length of 1.2 meters was divided at the center along the length. The sliced coated conductor was wound on a pair of bobbins with a diameter of around 4 cm and two pancake coils connected superconductively without a resistive joint were prepared. By flipping one of the pancake coils, the magnetic field generated by each coil is to be aligned to the same direction and generate meaningful magnetic field while the magnetic fields of two spit coils are canceled without flipping. Permanent current was induced by flowing current to the coil immersed in liquid nitrogen pool using a power supply. A magnetic field of 48.8 Gauss was generated when 20 A of current was flowing in the pancake coils. The "Wind and flip" method can be applied for the fabrication of a long solenoid magnet by winding a sliced coated conductor on a cylindrical bobbin. It is also introduced that the construction of multiple sets of pancake (or solenoid) coils is possible by a "wind-and-flip" method using a wide coated conductor.

• 에너지공학
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• 제20권3호
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• pp.185-190
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• 2011

본 논문은 초전도 에너지 저장장치(SMES)용 전도냉각형 고온초전도 자석의 설계, 제작 및 평가에 대해 기술한다. 고온초전도 자석은 황동 안정화재를 갖는 2개의 Bi-2223 다심 선재가 적층된 4-ply 도체로 제작된 22개의 double pancake coil(DPC)로 구성된다. 그리고, 각 DPC는 내경과 외경이 각각 500 mm, 691 mm이고 높이가 10 mm인 2개의 single solenoid coil로 구성된다. 코일 내부의 전기적 손실에 의해 발생된 열의 냉각을 위하여 DPC 사이에 두께 3 mm의 알루미늄 판이 내재된다. 고온초전도 자석은 2단 Gifford McMahon 냉동기에 의해 5.6 K까지 냉각된다. 충전전류가 증가할수록 방전시 고온초전도에서의 최대 온도가 증가 하였다. 충전전류가 360 A일 때 ��치 없이 고온초전도 자석에 1 MJ의 자기에너지가 성공적으로 저장되었다. 본 연구에서는 SMES용 전도 냉각형 고온초전도자석에 대한 열적, 전자기적 특성을 보이고, 본 연구를 통해 얻어진 결과는 전도냉각형 고온초전도자석의 최적설계 및 안정도 평가에 활용될 것이다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.363-367
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• 2005

발사체 자세제어용 추력기로 하이드라진 단일 추진제 방식이 널리 적용되며, 발사체 자세제어용 추력기 시스템은 신뢰성을 높이는 것이 중요한 요구조건의 하나다. 이를 위해 추력기 시스템에서 연료저장 탱크로부터 공급되는 하이드라진을 추력기들로 공급 또는 차단하는 밸브로 래칭 밸브를 적용한다. 래칭 밸브를 적용함으로서 밸브의 특성상 전원이 공급되지 않을 경우에도 공급(열림) 또는 차단(닫힘)의 상태를 계속하여 유지할 수 있으므로 여러 경우에 있어 신뢰성 있게 사용할 수 있다. 즉 래칭 밸브는 개폐명령에 대하여 솔레노이드 밸브와 같이 동작함과 아울러, 전원이 꺼진 상태에서도 마지막 작동 상태를 유지할 수 있는 기능이 추가된 형태이며, 이러한 래칭 메커니즘을 구현하기 위해서는 적절한 메커니즘이 구현되어야 한다. 본 논문에서는 45N급 하이드라진 래칭 밸브의 개발을 목표로 지상시험용 래칭 밸브의 설계 및 시험내용을 기술하였다. 밸브를 구성하기 위한 기본 구성품과 래칭 기능을 위한 메커니즘 등을 제시하였으며, 특히 밸브의 래칭 기능을 구현하기 위한 메커니즘으로 판스프링을 이용한 기계식 방식이 아닌 영구자석을 활용한 자기잠금 방식에 대해 상세하게 기술하였다. 또한 기밀시험, 작동시험, 사이클 시험 등을 통해 개발된 래칭 밸브의 설계요구 조건 부합여부를 확인하였으며, 본 하이드라진 추력기 시스템 래칭 밸브 시제품 개발을 통해 추력기의 국산화 개발 안정성 향상할 수 있었다.

• 한국정밀공학회지
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• 제19권12호
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• pp.109-119
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• 2002

In this paper, mechanism design of optical pickup actuator for fast access is proposed. This actuator is composed of moving magnet type actuator and moving coil type actuator for tracking and fine motion, respectively. Moving magnet type tracking actuator is configurated by two permanent magnets and four air-core solenoids. Additional damper by induced current in tracking actuator can reduce the transient vibration between the coarse seeking servo and fine seeking servo. Variable stiffness can be acquired by applying current to air-core solenoid simply. This actuator can achieve fast access by these additional damper and stiffness. Performance of this actuator is predicted through the FEM, simulation and simple experiment. Settling time for transient vibration is reduced to 14.7% according to simulation result.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권4호
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• pp.159-164
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• 2002

This paper presents the design and fabrication of a high-Tc superconducting (HTS) power supply for charging of the HTS magnet load, and its characteristics have been analyzed through experiments. HTS power supply consists of two heaters, an electromagnet, a Bi-2223 solenoid and a Bi-2223 pancake magnet load. In this experiment, 331 mH electromagnet and 0.8 A dc heater current were used, and 8.5 sec and 17 sec were used for pumping period. Mechanism of the superconducting switch is used for heater-trigger. In order to measure the pumping-current with respect to the magnet flux changes, hall sensor was installed at the center of the Bi-2223 pancake load. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping-current has reached about 1.2 A. In computer simulation, the maximum pumping-current of the system has been predicted to be about 2.7 A.

• Journal of Electrical Engineering and Technology
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• 제8권6호
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• pp.1320-1327
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• 2013

In this paper, two different electromagnetic energy harvesters using bulk micromachined silicon spiral springs and Polydimethylsiloxane (PDMS) packaging technique have been fabricated, characterized, and compared to generate electrical energy from ultra-low ambient vibrations under 0.3g. The proposed energy harvesters were comprised of a highly miniaturized Neodymium Iron Boron (NdFeB) magnet, silicon spiral spring, multi-turned copper coil, and PDMS housing in order to improve the electrical output powers and reduce their sizes/volumes. When an external vibration moves directly the magnet mounted as a seismic mass at the center of the spiral spring, the mechanical energy of the moving mass is transformed to electrical energy through the 183 turns of solenoid copper coils. The silicon spiral springs were applied to generate high electrical output power by maximizing the deflection of the movable mass at the low level vibrations. The fabricated energy harvesters using these two different spiral springs exhibited the resonant frequencies of 36Hz and 63Hz and the optimal load resistances of $99{\Omega}$ and $55{\Omega}$, respectively. In particular, the energy harvester using the spiral spring with two links exhibited much better linearity characteristics than the one with four links. It generated $29.02{\mu}W$ of output power and 107.3mV of load voltage at the vibration acceleration of 0.3g. It also exhibited power density and normalized power density of $48.37{\mu}W{\cdot}cm-3$ and $537.41{\mu}W{\cdot}cm-3{\cdot}g-2$, respectively. The total volume of the fabricated energy harvesters was $1cm{\times}1cm{\times}0.6cm$ (height).

• 한국초전도ㆍ저온공학회논문지
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• 제17권2호
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• pp.31-35
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• 2015

Mapping is a useful tool in the magnetic field analysis and design. In some specific research area, such as the nuclear magnetic resonance (NMR) or the magnetic resonance imaging (MRI), it is important to map the magnetic field in the interesting space with high accuracy. In this paper, an indirect mapping method in the center volume of an air-core solenoid is presented, based on the solution of the Laplace's equation for the field. Through the mathematical analysis on the mapping calculation, we know that the condition number of the matrix, generated by the measurement points, can greatly affect the error of mapping result. Two different arrangement methods of the measurement points in field mapping are described in this paper: helical cylindrical line (HCL) method and parallel cylindrical line (PCL) method. According to the condition number, the HCL method is recommended to measure the field components using one probe. As a simple example, we mapped the magnetic fields in a MRI main magnet system. Comparing the results in the different methods, it is feasible and convenient to apply the condition number to reduce the error in the field mapping calculation. Finally, some guidelines were presented for the magnetic field mapping in the center volume of the air-core solenoid.

• 대한의용생체공학회:의공학회지
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• 제35권4호
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• pp.105-110
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• 2014

For the combination of MRI and magnetic particle hyperthermia(MPH), we investigated the relative heating efficiency with respect to the strength of the static magnetic field under which the magnetic nanoparticles are to be heated by RF magnetic field. We performed nanoparticle heating experiments at the fringe field of 3T MRI magnet with applying the RF magnetic field perpendicularly to the static magnetic field. The static field strengths were 0T, 0.1T, 0.2T, and 0.3T. To prevent the coil heat from conducting to the nanoparticle suspension, we cooled the heating solenoid coil with temperature-controlled water with applying heat insulators between the solenoid coil and the nanoparticle container. We observed significant decrease of heat generation, up to 6% at 0.3T(100% at 0T), due to the magnetic saturation of the nanoparticles of 15 nm diameter under the static field. We think MPH is still feasible at low magnetic field lower than 0.3T if stronger RF magnetic field generation is permitted.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.318-321
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• 2002

Superconductivity has various applications in the whole industry such as the generation of high magnetic field for medical care and diagnosis, the lossless power transmission, environment-friendly vehicles and clean energy storage systems. This paper deals with the High-Tc superconducting(HTS) power supply using heater-triggered switch for the charging of the superconducting magnets. HTS superconducting power supply consists of two heaters, an electromagnet, and Bi-2223 solenoid and Bi-2223 pancake is used as a superconducting load, similar to real HTS magnet. The timing sequential control of two heaters and an electromagnet is an important factor to generate pumping- current in the Bi-2223 load. The thermal analysis of switching parts of the Bi-2223 solenoid according to the heater input was carried out. Based upon the analysis, the 0.8A of heater current were optimally derived. The maximum pumping current reached 1.7A.

• 대한기계학회논문집A
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• 제24권5호
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• pp.1166-1174
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• 2000

In this paper, we introduce a positioner based on magnetic levitation to eliminate the friction which is the most severe effect to limit high resolution on the micro level. Differently from existing electromagnetic device, the proposed positioner consists of air core solenoid and permanent magnet. Although the combination produces small magnetic force, it is suitable for realizing micro motion repeatedly without the accumulation of error because there is no hysteresis caused by ferromagnetic materials, no eddy current loss, no flux saturation. First, the approximate modeling of stiffness and damping effects between the magnetic elements is made and verified experimentally. Then, we have formulated the dynamic equation of one d.o.f magnetic levitation positioner using linear perturbation method and discussed the necessity of optimization for the chief design parameters to maximize the stability performance.