• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.3
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• pp.181-187
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• 2020

In this study, we propose a spherical flux concentration structure for omnidirectional wireless power transfer. Omnidirectional wireless power transfer technology is a method that can transmit power to a transmitter located in an arbitrary position in a two-dimensional or three-dimensional space. However, to improve the power transfer distance in a wireless power transfer system, the diameter of the coil or the number of windings must increase, thereby increasing the size of the transmitter. The proposed transmitter structure adds a ferrite core inside the transmitter coil so that the magnetic flux generated by the transmitter is directed toward the position of the receiver. As a result, the flux linkage and the mutual inductance increase. By implementing the omnidirectional wireless power transfer system using the proposed structure, the power transfer distance can be improved by 65% compared with the conventional system without increasing the size of the transmitter. Simulation shows that the proposed spherical flux concentration structure increases the mutual inductance of the omnidirectional wireless power transmission system.

• Progress in Superconductivity and Cryogenics
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• v.9 no.2
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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.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.210-212
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• 1996

A nonlinear optimization method for the shape optimization of actively shielded superconducting MRI magnet is presented. The presented design method can optimize both main coil and shielding coil simultaneously by setting constraints on stray field intensity at a specified distance from the magnet center. A 1 Tesla actively shielded superconducting MRI magnet, with 30cm bore diameter, is designed using the presented method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1712-1720
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• 2016

AC and DC insulation breakdown voltage was studied for magnet wire coated with double layers of high flexural PAI layer and high anti-corona PAI/nanosilica (15 wt%) layer. The specimens were prepared at various drying temperatures (T/D): $22^{\circ}C$, $240^{\circ}C$, and $260^{\circ}C$, respectively. The increase effects of nanosilica on AC and DC insulation breakdown voltage were not so significant compared to that of magnet wire coil coated with original PAI. And the AC and DC insulation breakdown voltage was improved by decreasing diameter of winding coil. As T/D temperature increased, AC and DC insulation breakdown voltage decreased.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2000.04a
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• pp.201-207
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• 2000

This study was carried out to optimize burner and heat exchanger of the condensing gas boiler which can save energy by utilizing latent heat of combustion gas and reduce pollutant in exhaust gas. The heat exchanger of the gas boiler was composed of three parts, which were an upper. lower , and coil heat exchanger . The upper heat exchanger was placed outside of the premixed burner and a lower heat exchanger was located under the upper heat exchanger. And, coil heat exchanger rounded the outer surface of an upper and lower heat exchanger. The boiler designed by this research reaches turn-down ratio 4 : 1 in the domain of equivalence ratio 0.75-0.8 and thermal efficiency of 97% . Emission of NOx and CO concentration was under 20ppm and 140ppm at equivalence ratio 0.8 . When diameter of the burner replace 60mm by 50mm. emission of CO was reduced about 50ppm remarkably.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.1
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• pp.24-29
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• 1996

Magnetic field theories for the design of highly homogeneous magnet are introduced and a nonlinear optimization method for the design of actively shielded superconducting magnet is presented. The presented design method can optimize both main coil and shielding coil simultaneously by setting constraints on stray field intensity at a specified distance from the magnet center. A 2-Tesla actively shielded superconducting magnet, with 90cm bore diameter, is designed using the presented method. The field homogeneity is 2ppm/30cm DSV and the 5 gauss stray field contour is within 4m axially and 3m radially from the magnet center. (author)., 7 refs., 6 figs., 3 tabs.

• The Journal of the Korea Contents Association
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• v.12 no.7
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• pp.247-254
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• 2012

This study presents the assessment results of coil length characteristics according to the volume of cerebral artery among the inpatients that received angiography and coil embolization following intracranial aneurysm from March, 2010 to September 2011. The volume rendering method was applied to the patients that received embolization to their cerebral arteries to obtain volume measurements. After coil embolization, the volume ratios were calculated with the volumes and lengths of coils. The embolic volume ratios were $43.11{\pm}3.11%$, $36.07{\pm}2.03%$, 40.91%, and 38.25% when the aneurysm sizes were 6mm or less, 6~10mm, 10~15mm and 20mm or more, respectively, being similar to the recommended volume ratios. Regardless of the types of aneurysm, the coil length according to volume was 0.65cm per $1mm^3$ of 20~$100mm^3$ when one type of 0.25mm diameter coil was used. They were 0.62cm per $1mm^3$ of 20~$150mm^3$ when one type of coil was used in the aneurysm volume of the saccular type and 0.60cm per $1mm^3$ of 20~$90mm^3$ when one type of coil was used in the aneurysm volume of the multi-lobulated type.

• Clinical and Experimental Pediatrics
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• v.48 no.2
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• pp.158-164
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• 2005

Purpose : We reviewed the therapeutic results of various Duct-Occlud coils(pfm AG, $K{\ddot{o}}ln$, Germany) to evaluate the efficacy of the most-recently modified Duct-Occlud coil(Nit-Occlud) in the transcatheter closure of patent ductus arteriosus(PDA), including large defects more than 4 mm in diameter. Methods : Two hundred and five patients who underwent percutaneous PDA occlusion using Duct-Occlud devices from March 1996 to December 2003 were enrolled and four types of Duct-Occlud [Standard(S), Reinforced(R), Reinforced reverse cone(RR) and Nit-Occlud(N)] were used in this study. The patients were followed up by echocardiogram and physical examination before discharge, one month, six months and 12 months after the procedure. Results : The rate of residual shunt according to the type of Duct-Occlud were as follows : S-54%, R-72%, RR-50%, N-14%(P<0.05 compared with other devices) at one month, S-25%, R-44%, RR-37%, N-0%(P<0.05 compared with other devices) at six months, S-8%, R-8%, RR-4%, N-0%(P<0.05 compared with S and R) at 12 months and later. Nit-Occlud coil showed the complete occlusion of PDA after six months of follow-up, even in 12 patients with relatively large PDA(>4 mm). Conclusion : The transcatheter closure of PDA using Duct-Occlud was an effective treatment and our study revealed that a Nit-Occlud coil which showed higher rate of occlusion even in PDA with large diameters over than 4 mm, was a more effective modality compared to previous devices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1492-1499
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• 2001

In order to develop the compact and flexible heat exchangers, we made the helically coiled heat exchangers. They can be manufactured with small diameter copper tubes without the need for fins; inner diameter=1.0 mm, straight tube length=1.5 m. The experiments were carried out with the following conditions; evaporation pressure=0.6 MPa, air velocity=0.7 ∼ 1.7 m/s, and working fluid=R-22. Pressure drop and heat transfer coefficient of heat exchangers were experimented according to the air velocity. The results of heat transfer coefficient show a 35% beneficial increase fur these heat exchangers over the other covered fin-tube heat exchangers. A cooling capacity of about 3 kW was obtained with an air velocity of 1.5 m/s. The distribution header has also been designed fur efficient distribution of refrigerant flow.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.650-657
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• 2001

This paper explains the process of designing a shielded encircling remote field eddy current (RFEC) probe to inspect nuclear fuel cladding tubes and investigates resulting signal characteristics. To force electromagnetic energy from exciter coil to penetrate into the tube, exciter coil is shielded outside by laminations of iron insulated electrically from each other. Effects of shielding and the proper operating frequency are studied by the finite element analysis and the location for sensor coil is decided. However, numerically simulated signals using the designed probe do not clearly show the defect indication when the sensor passes a defect and the other indication appeared as the exciter passes the defect is affected by the shape of shielding structure, which demonstrates that the sensor is directly affected by exciter fields. For this reason, the sensor is also shielded outside and this shielding dramatically improves signal characteristics. Numerical modeling with the finally designed probe shows very similar signal characteristics to those of inner diameter RFEC probe. That is, phase signals show almost equal sensitivity to inner diameter and outer diameter defects and the linear relationship between phase signal strength and defect depth is observed.