• Journal of electromagnetic engineering and science
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• v.11 no.3
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• pp.143-151
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• 2011

This paper presents a survey of recent wireless power transfer systems. The issue of wireless power transfer is to achieve a highly efficient system with small positioning errors of the facilities setting. Several theories have been presented to obtain precise system design. This paper presents a summary of design theory for short range power transfer systems and detailed formulations based on a circuit model and an array of infinitesimal dipoles. In addition to these theories, this paper introduces a coil array scheme for improving the efficiency for off axis coils. In the microwave range, tightly coupled resonators provide a highly efficient power transfer system. This paper present san-overlay resonator array consisting of half wavelength microstrip line resonators on the substrate with electromagnetically coupled parasitic elements placed above the bottom resonators. The tight couplings between the waveguide and the load resonator give strong power transmission and achieve a highly efficient system, and enables a contact-less power transfer railroad. Its basic theory and a demonstration of a toy vehicle operating with this system are presented. In the last topic of this paper, harmonic suppression from the rectenna is discussed with respect to acircular microstrip antenna with slits and stubs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.7
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• pp.566-569
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• 2018

A power line coupler that can apply high-frequency power to a railway overhead line structure was analyzed. It is difficult to supply auxiliary power to an overhead line in a high-voltage environment, and doing so requires a long-distance transfer. A method is proposed that utilizes the resonance on the Rogowski coil, which does not use a magnetic core. A simple overhead line structure was fabricated that consisted of a contact wire, messenger wire, and dropper. Couplers of various sizes were fabricated and deployed on the messenger wire, and the transfer characteristics of the two couplers were compared at a distance. As a result of applying the matching circuit to the coupler, the transmission efficiency was 53% at a distance of 2.5 m. The proposed method shows that it is possible to apply the auxiliary power by using the existing conductor in a special structure, such as the overhead line.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.5
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• pp.359-365
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• 2018

Herein, electromagnetic shielding structures to reduce the external noise coupling to printed spiral coils (PSCs) and a design method for improving the bandwidth of shielded PSCs have been proposed. It has been demonstrated that the bandwidth of shielded PSCs is limited due to the parasitic capacitance between the coils and the shielding structures and is confirmed by the transfer function simulation of the shielded PSCs with a transmission line as the radio-frequency interference noise source. A design method for the bandwidth improvement of the shielded PSCs has been proposed based on the equivalent circuit model analysis and the case studies depending on PSC designs with a three-dimensional field simulation. With the design method, an optimized shielded PSC design has been presented and successfully confirmed by experimental verification in that the optimized design results in a significant bandwidth improvement.

• Investigative Magnetic Resonance Imaging
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• v.24 no.3
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• pp.95-122
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• 2020

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). High-quality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B₁|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B₁| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B₁|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.717-719
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• 2001

This paper deals with simulation of the three-phase dc reactor type fault current limiter(FCL). This is a preliminary step to develop the FCL's faculties for an application to high voltage transmission line. A three-phase dc reactor type FCL consists of transformers, diodes, and a superconducting coil. By this simulation for the short-circuit test we can investigate the safety of FCL's elements. And, result of simulation will contribute parameter toward optimal design.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.68-71
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• 2001

This paper deals with the operational characteristics of the three-phase modified bridge type fault current limiter(FCL) for 3.3kV/200A power system. This is a preliminary step to develop the FCL's faculties for an application to high voltage transmission line. A three-phase modified bridge type FCL consists of transformers, diodes, and a high-Tc superconducting coil. As the results of simulations, when the FCL of 1.5H inductance was installed in the power system. the fault current was reduced to be about 90% of that without FCL.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.990-992
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• 1993

Studies have been made to establish what coil design parameters have an important influence on the amplitude of interturn voltages developed in a machine winding subject to steep-fronted surges. The studies are based on a lattice-diagram model of multi conductor transmission line in a machine winding energised by a simple ramp function. Variations in interturn voltages produced by changes in insulation thickness, insulation permittivity, surge wave-front are examined and certain guidelines for avoiding high interturn voltages are evaluated.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.285-290
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• 2002

Power systems are becoming larger and larger for meeting electric power demand. Therefore, the over-currents resulting from contingencies such short circuits are increasing higher. The Maximum short circuit current of modern power system is becoming so large that circuit breaker are not expected th be able to shut down the current in the future. In order to cut over-currents, a system composed of a superconducting fault current limiter(SFCL) and traditional breaker seems to provide a promising solution for future power operation. In present paper, three line-to-ground fault is assumed to happen at the center of 345kV transmission lines in a large capacity electric power system The superconducting fault current limiter was represented using a commutation type, which consists of a non-inductive superconducting coil and current limiting element(resistor or reactor). The introduction merits of the SFCL were investigated quantitatively by RTDS/EMTDC from the viewpoint of current limiting performance, the prevention of the voltage drop at the load bus and comparison characteristics for two type SFCL. Desired design specification and operation parameters of SFCL were also given qualitatively by the performance evaluation of the two type SFCL in the power system.

• Progress in Medical Physics
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• v.15 no.1
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• pp.54-58
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• 2004

The aim of this study was to develop special birdcage resonators for small objects including the human wrist, hand and small animals, using 3T MRI/MRS. Before substantial development, different types of parameters were arranged, based on theoretical analysis, through lumped element transmission line theory. The primary analysis was peformed with a network analyzer (HP 4195A) and the final experimental analysis was carried out with 3T MRI (Medinus, Korea). The manufactured birdcage resonator is typically composed of 12-element structures to which a low-pass filter is fundamentally applied. The diameter and length of each element of the birdcage resonator were as follows: (1) diameter 12 cm, length of element 22 cm, (2) diameter 15 cm, length of element 22 cm, and (2) diameter 17 cm, length of element 25 cm. Copper tape with a width of 1 cm was used for the coils. MRI acquisition parameters were TR=500 ms, TE=17 ms, and Ave=2 for T1-WT images, and TR=4,000 ms, TE=96 ms, and Ave=2 for T2-WT images. The ratio of the samples diameter to the birdcage resonators diameter was approximately 55%, 63% and 70%, respectively, for the three elements. This study determined that the best image quality and S/N ratio were obtained when the ratio of the object's diameter was approximately 50∼80%. A general theoretical analysis of the birdcage coil differs in many respects from the experimental results which were influenced by many factors that were not considering when the general theoretical analysis of the birdcage coil was peformed. The induced resistance may be considered as part of the resistive loss if the quantitative value can be determined using a radiation resistance approach.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.3
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• pp.74-83
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• 2002

The maximun short circuit current of modern power system is becoming so large that circuit breaker is not expected to be able to shut down the current in the future In order cut over-currents, a system composed of a superconducting fault current limiter(SFCL) and traditional breaker seems to provide a promising solution for furture power operation. In present paper, three line-to-ground fault is assumed to happen at the center of 345kV transmission lines in a large capacity electric power system. The superconducting fault current limiter was represented using a commutation type, which consists of a non-inductive superconducting coil and current limiting element (resistor or reactor). from the viewpoint of current limiting performance, the prevention of the voltage drop at the load bus and comparision characteristics for two type SFCL. Desired design specification and operation parameters of SECL were also given qualitatively by the performance.