• Progress in Superconductivity and Cryogenics
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• v.18 no.1
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• pp.46-49
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• 2016

The wireless power transfer (WPT) system using a magnetic resonance was based on magnetic resonance coupling of the transmission and the receiver coils. In these system, it is important to maintain a high quality-factor (Q-factor) to increase the transmission efficiency of WPT system. Our research team used a superconducting coil to increase the Q-factor of the magnetic resonance coil in WPT system. When the superconductor is applied in these system, we confirmed that transmission efficiency of WPT system was higher than normal conductor coil through a preceding study. The efficiency of the transmission and the receiver coil is affected by the magnetic shielding effect of materials around the coils. The magnetic shielding effect is dependent on the type, thickness, frequency, distance, shape of materials. Therefore, it is necessary to study the WPT system on the basis of these conditions. In this paper, the magnetic shield properties of the cooling system were analyzed using the High-Frequency Structure Simulation (HFSS, Ansys) program. We have used the shielding materials such as plastic, aluminum and iron, etc. As a result, when we applied the fiber reinforced polymer (FRP), the transmission efficiency of WPT was not affected because electromagnetic waves went through the FRP. On the other hand, in case of a iron and aluminum, transmission efficiency was decreased because of their electromagnetic shielding effect. Based on these results, the research to improve the transmission efficiency and reliability of WPT system is continuously necessary.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1258-1260
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• 2005

Superconducting synchronous motors and generators have the field coil composed of superconductor with almost zero resistance at superconducting state. Therefore, co or loss at the conventional field coil is eliminated and the superconducting machine gets higher efficiency. The armature coil of the superconducting machine is composed of cower wire and supported by non-magnetic material such as FRP(Fiber Reinforced Plastic). Although a fully-superconducting machine with superconducting armature coil has been researched, it was not developed toward industrial application because of AC transporting loss and difficulty in construction of the cooling structure and so on. This paper contains the design procedure of a 1 MW superconducting synchronous motor using high-temperature superconductor only for the field coil. Especially, the armature coil is designed by water-cooling in order to dissipate Joule heat easily. Moreover, 3-dimensional electromagnetic design is conducted to get a proper design result and reduce design errors from 2-dimensional approach.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.72-76
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• 2003

We developed a polarimetric fiber-optic current sensor using a length of twisted fiber and a Faraday rotator mirror which was used to suppress the linear birefringence effect. A gold coated mirror was also used as the sensor coil reflector, and the results were compared with the case of FRM. From the experimental results, it is clear that the FRM greatly enhances the stability of the fiber optic current sensor output..

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.419-427
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• 1996

Thermally-stabilized fiber-optic current sensors are proposed and demonstrated. The sensor head is made of two coil formers combined perpendicularly. In this sensor head, bending-induced birefringences can be reduced to the level much smaller than those of the single former type because the eigen-axes of the two perpendicular coil formers are made orthogonal to each other. Moreover, thermal variation of the birefringence is also expected to be minimized by the orthogonality of the two polarization eigen-axes. We changed the temperature slowly in the range of 20~45$^{\circ}C$ during 100 minutes. The overall linearity of the sensor is better than 1.2% in the range of 0~1000A. The long-term fluctuation of the sensor is less than 1% when measured for 3 hours at 500A and room temperature. Two orthogonally-polarized laser diodes are combined together to make the incident beam unpolarized. In the signal processing, the signals are separated by two parts and normalized respectively, which minimize the efects of optical fluctuations coming from sources, connectors, etc.

• Journal of Sericultural and Entomological Science
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• v.39 no.2
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• pp.186-196
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• 1997

The IR crystallinity index of Calcium nitrate treated silk fiber decreased proportionally to the concentration of calcium nitrate. A partial change of conformation was observed in the concentration of over 46.4-47.6% changing from $\beta$-sheet or to random coil in the crystalline region. This is in coincidence with the result of crystallinity index, which was started to be reduced in the concentration range of 46.4-47.6%. A same trend was observed for the X-ray order factor, birefringence, degree of orientation and surface structure. These structural parameters were remarkably changed on the treatment of silk fibers with concentration of 46.4-17, 6% calcium nitrate. Therefore, it seems that there exists a critical concentration of calcium nitrate in affection the structure and morphology of silk fibers. According to the examination of surface morphology, the fine stripe was observed in the direction of fiber axis at 46.4% concentration. However, the treated concentration was exceeded by 47.6%, the cracks were appeared severely on the fiber surface in the transverse direction as well as fiber axis direction. This result might be related to the tensile properties, specially a tenacity of silk fibers. As a result of quantitative analysis of a dilute acid hydrolysis, three different regions, which are known as a amorphous, semi-crystalline and crystalline region, could be obtained. The hydrolysis rate curves were different with various concentrations of treatment and the relative contents of each region could be calculated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.1
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• pp.31-36
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• 2014

This paper shows the feasibility of using carbon-fiber-reinforced polymer (CFRP) composite materials for manufacturing automotive coil springs. For achieving weight reduction by replacing steel with composite materials, it is essential to optimize the material parameters and design variables of the coil spring. First, the shear modulus of a CFRP beam model, which has $45^{\circ}$ ply angles for maximum torsional stiffness, was calculated and compared with the test results. The diameter of the composite spring was predicted to be 17.5 mm for ensuring a spring rate equal to that when using steel material. Finally, a finite element model of the composite coil spring with $45^{\circ}$ ply angles and 17.5 mm wire diameter was constructed and analyzed for obtaining the static spring rate, which was then compared with experimental results.

• Journal of the Optical Society of Korea
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• v.2 no.2
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• pp.74-79
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• 1998

The use of a fiber Fabry-Perot interferometer (FFPI) as an optical current transducer is demonstrated. A conventional inductive pickup coil converts the time-varying current I(t) being measured to a voltage waveform V(t) applied across a piezeolectric strip to which the FFPI is bonded. The strip experiences a longitudinal expansion and contraction, resulting in an optical phase shift ${\phi}(t)$ in the fiber proportional to V(t). This phase shift is measured using a frequency-modulated semiconductor light source, photodiodes to monitor the reflected light from the FFPI and the laser power, and a digital signal processor. Calibration routines compute V(t) and I(t) from the measured phase shift at a l KHz rate. Response to 60 Hz ac over the design range 0-1300A rms is characterized Transient response of the FFPI transducer is also measured.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.38-40
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• 2001

Fiber-optic current sensor was developed using the Faraday effect to measure the electrical current on high-voltage lines. A twisted single-mode optical fiber was used as a sensor coil to suppress birefringence effect, enhancing performance against environmental perturbations. In this paper, we report the basic design considerations and the preliminary experimental results carried out in the 1000 A input current range.

• Smart Structures and Systems
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• v.34 no.1
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• pp.41-50
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• 2024

The accurate measurement of temperature in the ground source heat pump system is crucial for assessing the thermal response of the system and validating the numerical model for parametric study, which is necessary for the thermal performance evaluation of the geothermal energy system. Conventional temperature sensors have some disadvantages such as they are difficult to install, and their position can be shifted during the backfill process of the ground heat exchanger. In this study, Fiber Bragg Grating (FBG) sensors were used to measure the temperature change of a recently developed ground heat exchanger (Coil Column Unit, CCU). FBG sensors were first calibrated in a thermal chamber alongside a correlation sensor (RTD sensor). The calibrated sensors were then mounted on the pipe surface at each spiral of the CCU to measure how temperature changes during the in-door mockup thermal response test. Finally, the measurement results of the FBG sensors were verified with a finite element coded program. The results indicated that the temperature difference between the numerical analysis and the experiment was less than 1%, which is significantly lower than that of the previous study using the RTD sensors. Therefore, it is feasible to apply FBG sensors for temperature measurement during the operation of the TRT of the geothermal energy system.

• Journal of Korea Society of Industrial Information Systems
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• v.24 no.2
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• pp.15-23
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• 2019

High temperature superconducting (HTS) generators for wind power systems are attractively researched with the advantages of high efficiency and smaller size compared with conventional generator. However, the HTS generators have high Lorentz force problem, which acts on HTS field coils due to their high current density and magnetic field. This paper deals with characteristic analysis of the modularized HTS field coil for a 750 kW superconducting wind power generator according to field coil structure. The modularized HTS field coil structure was designed based on the electromagnetic and mechanical analysis results obtained using a 3D finite element method. The electromagnetic force of the module coil was also analyzed. As a result, the perpendicular and maximum magnetic fields of the HTS coils were 2.5 T and 3.9 T, respectively. The maximum stress of the supports was less than the allowable stress of the glass-fiber reinforced plastic material, and displacement was within the acceptable range. The design specifications and the results of the HTS module coil structure can be effectively utilized to develop large-scale superconducting wind power generators.