• Current Optics and Photonics
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• v.3 no.4
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• pp.285-291
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• 2019

We have studied the behavior of light in the intermediate regime between a single nanoslit and an infinite nanoslit array. We first calculated the optical characteristics of a small number of nanoslits using finite element numerical analysis. The phase variance of the proposed nanoslit model shows a gradual phase shift between a single nanoslit and ideal nanoslit array, which stabilizes before the total array length becomes ${\sim}0.5{\lambda}$. Next, we designed a transmission-enhanced Fresnel zone plate by applying the phase characteristics from the small-number nanoslit model. The virtual-point-source method suggests that the proposed Fresnel zone plate with phase-invariant nanoslits achieves 2.34x higher transmission efficiency than a conventional Fresnel zone plate. Our report describes the intermediate behaviors of a nanoslit array, which could also benefit subwavelength metallic structure research of metasurfaces.

• Nuclear Engineering and Technology
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• v.52 no.11
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• pp.2491-2498
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• 2020

The paper concentrates on an experimental study of the pressure drop in double-layered packed beds formed by glass spheres, having the configuration of horizontal and vertical stratification. Both single-phase and two-phase flow tests are performed. The pressure drop during the test is recorded and the measured data are compared with those of homogeneous beds consisting of mono-size particles. The results show that for the horizontally stratified bed with fine particles atop coarse particles, the pressure drop in top layer is found higher than those of homogenous bed consisting of the same smaller size particles, while the measured pressure drop of bottom part is similar with those of similar homogenous bed. But for the homologous bed with upside-down structure, the stratification has little or no effect on the pressure drop of the horizontally stratified bed, and the pressure drop of each layer is almost same as that of homogeneous bed packed with corresponding spheres. Additionally, in vertically stratified bed, the pressure drops on the left and right side is almost equal and between those in homogeneous beds. It is speculated that vertically stratified structure may lead to lateral flow which redistributes the flow rate in different parts of packed bed.

• Korean Journal of Materials Research
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• v.27 no.7
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• pp.369-373
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• 2017

Unidirectionally solidified TiAl alloys were prepared by optically-heated floating zone method at growth rates of 10 to 70 mm/h in flowing argon. The microstructures and tensile properties of these crystal bars were found to depend strongly on the growth rate and alloy composition. TiAl alloys with composition of 47 and 50 at.%Al grown under the condition of 10 mm/h showed $Ti_3Al({\alpha}_2)/TiAl({\gamma})$ layer structures similar to single crystals. As the growth rate increased, the alloys with 47 and 50 at.%Al compositions showed columnar-grain structures. However, the alloys fabricated under the condition of 10 mm/h had a layered structure, but the alloy with increased growth rate consisted of ${\gamma}$ single phase grains. The alloy with a 53 at.%Al composition showed a ${\gamma}$ single phase regardless of the growth rate. Room-temperature tensile tests of these alloys revealed that the columnar-grained material consisting of the layered structure showed a tensile ductility of larger than 4 % and relatively high strength. The high strength is caused by stress concentration at the grain boundaries; this enhances the secondary slip or deformation twinning across the layered structure in the vicinity of the grain boundaries, resulting in the appreciable ductility.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.960-962
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• 2005

In this paper, we investigated the quench characteristics of high-Tc superconducting(HTSC) elements in the integrated three-phase flux-lock type superconducting fault current limiter(SFCL) according to fault types such as the single-line-to-ground fault, the double-line-to-ground fault, the line-to-line fault and the triple-line-to-ground fault. The integrated three-phase flux-lock type SFCL is an upgrade version of single-phase flux-lock type SFCL. The structure of the integrated three-phase flux-lock type SFCL consisted of a three-phase flux-lock reactor wound on an iron core with the ratio of the same turn between coil 1 and coil 2 in each phase. When the SFCL is under the normal condition, the flux generated in the iron core is zero because the flux generated between two coils of each single phase is canceled out. Therefore, the SFCL's impedance is zero, and the SFCL has negligible influence on the power system. However, if a fault occurs in any single one of three phases, the flux generated in the iron core is not zero any more. The flux makes HTSC elements of all phases to quench irrespective of the fault type, which reduces the current in fault phase as well as the current of sound phase. It was obtained that the fault current limiting characteristics of the suggested SFCL were dependent on the quench characteristics of HTSC elements in all three phases.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.2
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• pp.46-52
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• 2012

This paper proposes a novel single-phase ac-ac converter topology based on the Z-source concept. The converter provides buck-boost function and plays the role of frequency changer. Compared to the traditional ac-dc-ac converter, it uses fewer devices, realizes direct ac-ac power conversion, and has a simpler circuit structure, so as to have higher efficiency and better circuit characteristics. Compared to the traditional matrix converter, it provides a wider voltage regulation range. The circuit topology, operating principle, control method and simulation results are given in this paper, and the rationality and feasibility is verified.

• Proceedings of the KIEE Conference
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• 2004.04a
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• pp.3-5
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• 2004

The single phase SRM has some demerits that has a torque ripple, noise and vibration because of being excited by switching pulse power source. Therefore, to make up for these demerits, it is realized many studies for the structure design used by computer and the operating methods by power electronic technique. On this paper, we will measure the accurate torque characteristics of the disk type single phase SRM, which is designed and manufactured for fan drive through the previous studies. With this results, we'll find the control elements to reduce the torque ripple and then design and manufacture the optimal drive circuit.

• Journal of Advanced Marine Engineering and Technology
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• v.17 no.5
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• pp.86-98
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• 1993

The application of A.C. motor for servo system is rapidly increased according to the recent advance of power electronics and digital control techniques. The induction motor which has a simple structure and needs less maintenance has become to be used widely in the industrial field for the speed and position control recently. In this paper, the full-bridge resonant inverter is applied to the speed control of single phase inducting motor. The digital PID control algorithm is used and the control parameter is determined by the Zigler-Nichols transient response method. The speed control is carried out by the one chip micro-processor(intel EV 8097BH) and control program is developed by the assembly language. By the experimental result, it is confirmed that the speed of single phase induction motor driven by full bridge series inverter can be smoothly controlled by a digital PID controller.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.2
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• pp.311-317
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• 2010

This paper deals with operation characteristics of a written-pole motor (WPM), having that of a permanent magnet (PM) synchronous motor and induction motor at once. The WPM also has a magnet layer on the surface of the rotor and the exciter pole that is a device to make the magnet layer magnetized during the operation. This study, introducing a fundamental structure and operation characteristics of a single-phase WPM, proposes a initial design method. With those ground, a 130W, single-phase WPM that is designed for a home appliance is presented and verified with a performance through the experiment.

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.1996-2003
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• 2018

In this paper, the design and characteristic analysis of a novel single-phase hybrid switched reluctance motor (HSRM) for the purpose of replacing the universal motor in commercial blenders are presented. The proposed motor is easy to manufacture due to its simple yet robust structure with minimized power switches and no torque dead-zone. Moreover, the proposed HSRM is able to deliver a high starting torque as a requirement for blending hard food or even ice. The stator has permanent magnets (PMs) mounted on its inner surface and the rotor has a wide pole arc and salient poles that contribute to its high starting torque profile and the elimination of the torque dead-zone. Finite element method (FEM) is used to analyze the characteristic of the proposed motor. Finally, the prototype is manufactured and its performance is verified through experiments.

• Journal of Power Electronics
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• v.14 no.3
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• pp.458-467
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• 2014

In this paper, a single-phase current-source bidirectional converter topology for V2G applications is proposed. The proposed converter consists of a single-phase current-source rectifier (SCSR) and an auxiliary switching network (ASN). It offers bidirectional power flow between the battery and the grid in the buck or boost mode and expands the output voltage range, so that it can be compatible with different voltage levels. The topology structure and operating principles of the proposed converter are analyzed in detail. An indirect control algorithm is used to realize the charging and discharging of the battery. Finally, the semiconductor losses and system efficiency are analyzed. Simulation and experimental results demonstrate the validity and effectiveness of the proposed topology.