• Progress in Superconductivity and Cryogenics
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• v.17 no.2
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• pp.45-49
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• 2015

It has been well known that a toroid is the inevitable shape for a high temperature superconducting (HTS) coil as a component of a large scale superconducting magnetic energy storage system (SMES) because it is the best option to minimize a magnetic field intensity applied perpendicularly to the HTS wires. Even though a perfect toroid coil does not have a perpendicular magnetic field, for a practical toroid coil composed of many HTS pancake coils, some type of perpendicular magnetic field cannot be avoided, which is a major cause of degradation of the HTS wires. In order to suggest an optimum design solution for an HTS SMES system, we need an accurate, fast, and effective calculation for the magnetic field, mechanical stresses, and stored energy. As a calculation method for these criteria, a numerical calculation such as an finite element method (FEM) has usually been adopted. However, a 3-dimensional FEM can involve complicated calculation and can be relatively time consuming, which leads to very inefficient iterations for an optimal design process. In this paper, we suggested an intuitive and effective way to determine the maximum magnetic field intensity in the HTS coil by using an analytic and statistical calculation method. We were able to achieve a remarkable reduction of the calculation time by using this method. The calculation results using this method for sample model coils were compared with those obtained by conventional numerical method to verify the accuracy and availability of this proposed method. After the successful substitution of this calculation method for the proposed design program, a similar method of determining the maximum mechanical stress in the HTS coil will also be studied as a future work.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.9
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• pp.72-80
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• 2009

When the magnet wheel rotates over a conducting plate, it generates the traction torque as well as the repulsive force on the conducting plate. Partially-cut traction torque results in the linear force into the tangential direction. To cut the traction torque, the concept of magnetic shield is introduced. The direction change of the linear force is realized varying the shielded area of magnetic field. That is, the tangential direction of non-shielded open area becomes the direction of the linear thrust force. Specially a shape of permanent magnets composing the magnet wheel leads to various pattern of magnetic forces. So, to enlarge the resulting force density and compensate its servo property a few simulations are performed under various conditions such as repeated pattern, pole number, radial width of permanent magnets, including shape of open area. The theoretical model of the magnet wheel is derived using air-gap field analysis of linear induction motor, compared with test result and the sensitivity analysis for its parameter change is performed using common tool; MAXWELL. Using two-axial wheel set-up, the tracking motion is tested for a copper plate with its normal motion constrained and its result is given. In conclusion, it is estimated that the magnet wheel using partial shield can be applied to a noncontact conveyance of the conducting plate.

• Progress in Superconductivity and Cryogenics
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• v.18 no.3
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• pp.21-24
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• 2016

Recently, production technique and property of the High-Temperature Superconductor (HTS) tape have been improved. Thus, the study on applying an HTS magnet to the high magnetic field application is rapidly increased. A Nuclear Magnetic Resonance (NMR) spectrometer requires high magnitude and homogeneous of central magnetic field. However, the HTS magnet has fabrication errors because shape of HTS is tape and HTS magnet is manufactured by winding HTS tape to the bobbin. The fabrication errors are winding error, bobbin diameter error, spacer thickness error and so on. The winding error occurs when HTS tape is departed from the arranged position on the bobbin. The bobbin diameter and spacer thickness error occur since the diameter of bobbin and spacer are inaccurate. These errors lead magnitude and homogeneity of central magnetic field to be different from its ideal design. The purpose of this paper is to investigate the effect of winding error, bobbin diameter error and spacer thickness error on the central field and field homogeneity of HTS magnet using the virtual NMR signals in MATLAB simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.6
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• pp.872-877
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• 2015

The Permanent Magnet (PM) machine used at speed control using field-weakening control method. But the field-weakening current, which reduces the field flux for high speeds, causes significant copper and core losses. Therefore, this paper deals with the PM performance evaluations in a pole changing memory motor (PCMM). The PCMM can change the number of magnetic poles and produce two types of torque. When the motor operates with eight poles, it produces a magnetic torque at low rotational speeds. When the motor changes to four poles, it produces both magnetic torque and reluctance torque at high speeds. The paper explain the principle and basic characteristics of the motor by using a finite element method magnetic-field analysis, which consists of a PM magnetized by a pulse d-axis current of the armature winding. The results of our experiment show that the proposed motor reduces core loss by 10% and 55% under no-load and load conditions, and doubles the speed range of the motor.

• Journal of the Korean Society of Safety
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• v.30 no.4
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• pp.8-13
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• 2015

The magnetic shape memory alloys have recently received a lot of attention due to the considerable progress achieved in understanding the particular importance and the development of the factors. Among these alloys, the ferromagnetic Co-Ni- alloys have been concerned specially because of the thermoelastic character of the fcc (g) - bct (a) martensitic transformation which exhibits under the action of the temperature (shape memory effect), the stress (superelasticity) and the magnetic field (magnetoelasticity). The morphological, the crystallographical, and the thermal characteristics of thermally induced martensite in Co-35.3Ni-11.3Al(wt.%) and Co-28.1Ni-47.4Fe-3.3Ti (wt.%) alloy have been investigated by the scanning electron microscope (SEM), the X-ray Diffraction (XRD), and the differential scanning calorimeter (DSC).

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.10
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• pp.545-553
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• 2002

This paper is about the analysis of 3-dimensional magnetic field distribution in CPM(Convergence Purity Magnet) considering magnetization vector and the optimum design of CPM. The magnetization vector of CPM is obtained using 2-dimensional magnetization FEA(Finite Element Analysis) coupled with Priesach model. Using this magnetization vector of CPM, we analysed the 2-dimensional and 3-dimensional magnetostatic field of CPM and know that these analysis results are not equal. From experimental result, we know that the 3-dimensional analysis is accurate because the magnetic field distribution in CPM cannot be considered correctly by 2-dimensional analysis because of the shape of CPM. Finally, the optimum designing of CPM which control accurately the electron beam deflection in CRT(Cathode Ray Tube) was possible using 3-dimensional magnetic field analysis result.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.696-699
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• 2003

In the semiconductor and the optical industry a new transport system which can replace the conventional sliding system is required. There systems are driven by magnetic field and conveyer belt. The magnetic field damages semiconductor and contact force scratches the optical lens. The ultrasonic wave driven system can solve these problem. In this paper, the object transport system using the excitation of ultrasonic wave is proposed. The experiments for finding the optimal excitation frequency, finding phase-difference between two ultrasonic wave generators are performed. The relationship of transporting speed according to the change of flexural beam shape is verified and the system performance for practical use is evaluated.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.25-29
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• 2003

In the semiconductor and the optical industry a new transport system which can replace the conventional sliding system is required. These systems are driven by magnetic field and conveyer belt. The magnetic field damages semiconductor and contact force scratches the optical lens. The ultrasonic wave driven system can solve these problem. In this paper, the object transport system using the excitation of ultrasonic wave is proposed. The experiments for finding the optimal excitation frequency, finding phase-difference between two ultrasonic wave generators are performed. The relationship of transporting speed according to the change of flexural beam shape is verified and the system performance for practical use is evaluated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.262-270
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• 2004

Basic experiments were carried out using the THT-IV low-power Hall thruster to examine the influences of magnetic field shape and strength, and acceleration channel length on thruster performance and to establish guidelines for design of high-performance Hall thrusters. Thrusts were measured with varying magnetic field and channel structure. Exhaust plasma diagnostic measurement was also made to evaluate plume divergent angles and voltage utilization efficiencies. Ion current spatial profiles were measured with a Faraday cup, and ion energy distribution functions were estimated from data with a retarding potential analyzer. The thruster was stably operated with a highest performance under an optimum acceleration channel length of 20 mm and an optimum magnetic field with a maximum strength of about 150 Gauss near the channel exit and with some shape considering ion acceleration directions. Accordingly, an optimum magnetic field and channel structure is considered to exist under an operational condition, related to inner physical phenomena of plasma production, ion acceleration and exhaust plasma feature. A new Hall thruster was designed with basic research data of the THT-IV thruster. With the thruster with many considerations, long stable operations were achieved. In all experiments at 200-400 V with 1.5-3 mg/s, the thrust and the specific impulse ranged from 15 to 70 mN and from 1100 to 2300 see, respectively, in a low electric power range of 300~1300 W. The thrust efficiency reached 55 %. Hence, a large map of the thruster performance was successfully made. The thermal characteristics were also examined with data of both measured and calculated temperatures in the thruster body. Thermally safe conditions were achieved with all input powers.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.522-522
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• 1996

An investigation of the effects of transverse magnetic field and Peltier effect on melt convection and macrosegregation in vertical Bridgman crystal grosth of Te doped InSb was been carried out by means of microstructure observation, Hall measurement, electrical resistivity measurement and X-ray analysis. Before the experiments, Interface stability, convective instability and suppression of convection by magnetic field were calculated theoretically. After doping 1018, 1019 cm-3 Te in InSb, the temperature of Bridgman furnace was set up at $650^{\circ}C$. The samples were grown in I.D. 11mm, 100mm high quartz tube. The velocity of growth was about 2${\mu}{\textrm}{m}$/sec. In order to obtain the suppression of convection by magnetic field in the middle of growth, 2-4KG magnetic field was set on the melt. For searching of the shape of solid-liquid interface and the actual velocity of crystal growth, let 2A current flow from solid to liquid for 1second every 50seconds repeatedly (Peltier effect). The grown InSb was polycrystal, and each grain was very sharp. There was no much difference between the sample with and without magnetic field at a point of view of microstructure. For the sample with Peltier effect, the Peltier marks(striation) were observed regularly as expected. Through these marks, it was found that the solid-liquid interface was flat and the actual growth velocity was about 1-2${\mu}{\textrm}{m}$/sec. On the ground of theoretical calculation, there is thermosolutal convection in the Te doped InSb melt without magnetic field in this growth condition. and if there is more than 1KG magnetic field, the convection is suppressed. Through this experiments, the effective distribution coefficients, koff, were 0.35 in the case of no magnetic field, and 0.45 when the magnetic field is 2KG, 0.7 at 4KG. It was found that the more magnetic field was applied, the more convection was suppressed. But there was some difference between the theoretical calculation and the experiment, the cause of the difference was thought due to the use of some approximated values in theoretical calculation. In addition to these results, the sample with Peltier effect showed unexpected result about the Te distribution in InSb. It looked like no convection and no macrosegregation. It was thought that the unexpected behavior was due to Peltier mark. that is, when the strong current flew the growing sample, the mark was formed by catching Te. As a result of the phenomena, the more Te containing thin layer was made. The layer ruled the Hall measurement. The values of resistivity and mobility of these samples were just a little than those of other reference. It was thought that the reason of this result was that these samples were due to polycrystal, that is, grain boundaries had an influence on this result.