• 한국항행학회논문지
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• 제22권2호
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• pp.148-153
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• 2018

본 논문에서는 복수 수신기에 전력을 전송하기 위한 SIMO (single-input multiple-output) 자기공진방식 무선전력전송 시스템을 제안하고, 이에 따른 시뮬레이션 및 측정결과를 제시하였다. 지름 600 mm 의 송신 단일루프 및 송신 헬리컬 공진 코일, 외경 900 mm 스파이럴 수신 공진 코일을 사용하고, $80{\times}60mm^2$ 평판 사각 코일을 수신으로 활용하여 600mm 떨어진 테이블 형태 구조로 무선전력전송 시스템을 구성하였다. 최적의 특성을 위해 무선전력전송 코일을 설계하고 3차원 전자계해석 및 등가회로 해석 시뮬레이션을 진행하고 이를 제작하여 전송 특성을 측정하였다. 스파이럴 공진코일의 중심부에서 거리에 따른 효율변화를 해석하였으며, 구성한 시스템의 측정결과 수신기가 1개일 경우의 효율은 57 % 이며, 2개로 수신될 경우 각각 37 %의 전송 효율을 나타내었다.

• 한국자동차공학회논문집
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• 제23권4호
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• pp.436-443
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• 2015

In order to develop the PHEV(plug-in hybrid electric vehicle), the specific power transmission systems considering the PHEV system characteristics should be applied. A PHEV applied to series-parallel type hybrid power transmission system is a typical example. In this paper, the novel hybrid power systems are proposed by analyzing the existing PHEV system. The backward simulation program is developed to analyze the fuel efficiency of hybrid power system. Quasi-static models for each components such as engine, motor, battery and vehicle are included in the developed simulation program. To obtain an optimal condition for hybrid systems, an optimization approach called the dynamic programming is applied. The simulation is performed in various driving cycles. A weakness for the existing system is found through the simulation. To compensate for a discovered weakness, novel hybrid power systems are proposed by adding or moving the clutch to the existing system. Comparing the simulation results for each systems, the improved fuel efficiency for proposed systems are verified.

• Journal of electromagnetic engineering and science
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• 제11권3호
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• pp.156-160
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• 2011

We have proposed and analyzed an equivalent circuit for a magnetically coupled wireless power transmission (WPT) system between two loop resonators by considering its coupling coefficient and radiation-related parameters. A complete formulation is provided for all the necessary circuit parameters. The mechanism of radiation loss is sufficiently explained. The circuit and electromagnetic (EM) simulation results have been shown to be in good agreement. Based on the proposed circuit formulation, a specific load impedance for maximum WPT efficiency was found to exist. The proposed modeling of the WPT in terms of circuit characterizations provides sufficient insight into the problems associated with WPT.

• Journal of electromagnetic engineering and science
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• 제10권4호
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• pp.219-223
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• 2010

Based on a provided closed-form wireless power transmission (WPT) efficiency formula, which may be used for any value of load, we have analyzed the WPT efficiencies between two metamaterial-inspired loop antennas in various aspects. Due to the modeling based on low frequency circuit theory, the provided formula at the center resonant frequency has been found to be accurate until when the distance between the two loop antennas increases to 15 cm (about $\lambda_0/6$ at 300 MHz). When the two loops get closer, the resonant frequency has been found to split into two in theory, simulations, and measurements. The EM-simulated and measured efficiencies at new resonant frequencies are 60.9 % and 46.3 %, respectively, at d=15 cm. With two extra rings around the loops, the maximum efficiency is enhanced to 93.7 % at d=15 cm. The effect of the additional two rings is about 30 %.

• 한국전자파학회논문지
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• 제23권5호
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• pp.624-631
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• 2012

본 논문은 Guanella의 1:1 transmission-line transformer와 harmonic filtering 방식을 이용한 13.56 MHz 고효율 전류 모드 D급(CMCD) 전력증폭기를 제안한다. 출력 정합 네트워크에 기존의 D급 전력증폭기의 부하 네트워크를 변형하여 harmonic filtering 방식을 포함시킴으로써 낮은 2차와 3차 고조파 특성을 얻었다. 제작된 CMCD 전력증폭기는 13.56 MHz의 CW 입력 신호를 사용하여 측정하였을 때, 13.4 dB의 전력 이득을 가지며, 44.4 dBm의 출력에서 84.6 %의 높은 PAE 특성을 나타내었다. 같은 출력에서 2차 3차 고조파는 각각 -50.3 dBc와 -46.4 dBc를 나타냈다.

• 전기학회논문지
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• 제64권4호
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• pp.623-628
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• 2015

In this paper, the shield plate was applied to the wireless power transfer (WPT) system. Then we compared transmission efficiency of WPT system between transmitter and receiver coils. The superconductor coil was applied to transmitter and receiver coils in order to increase the transmission efficiency of WPT. The superconductor coil was more effective to power transmission as its current density was higher than normal conductor coil. Efficiency of WPT between transmitter and receiver coils was changed by a quality of shielding. We used the shielding materials such as glass, iron, steels, aluminum etc. The efficiency of WPT system was depended on the shielding materials of transmitter and receiver coils. As a result, magnetic material such as aluminum, iron reduced the magnetic flux density and the efficiency of WPT. remarkably, but in non-magnetic material such as glass and plastic, the efficiency of WPT was unaffected.

• Tribology and Lubricants
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• 제12권3호
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• pp.107-114
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• 1996

MoS$_{2}$ bonded film was applied to reduction gears, and its lubricating properties were experimentally evaluated in terms of the power transmission efficiency and the frictional noise with a dynamo-typed gear test rig. Tests were performed in both oil lubrication and dry condition where the rotating velocity and loading torque were varied. In dry condition, MoS$_{2}$ bonded films effected the power transmission efficiency to increase about 5%, and the frictional noise level to decrease about 6 dB under the test operating conditions. It well proved that MoS$_{2}$ bonded films were a very effective solid lubricant for reduction gears. In oil lubricating conditions, the frictional properties of the coated gears were mainly governed by the lubricating oil, and lubricating effects of MoS2 bonded films were not evident. The result suggested that lubricating effect of MoS$_{2}$ bonded films would be limited to prevent a damage of reduction gears in the initial run when they were used in oil lubrication conditions.

• 한국전자파학회논문지
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• 제25권3호
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• pp.304-310
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• 2014

본 논문에서는 두 루프(공진체)를 이용한 자계 결합 무선 전력 전송 방식의 결합계수(k)와 공진기의 Q 값 그리고 수신부의 최적 부하($R_{L,opt}$)에 대하여 제한되는 전송 효율의 문제점을 극복하기 위해 메타 물질(SRR 또는 RR), 도체, Relay 방법 등을 무선 전력 전송 시스템에 삽입 또는 시스템 주변에 위치시켜 전송 효율 증가하는 방법을 연구하였다. 위 방법을 통해 각 Case 결과에 따라 11~60 % 이상의 효율 증가를 확인할 수 있었다. 각기 다른 물질을 이용하여 전송 효율이 증가되는 최적의 방법을 관찰하였으며, EM 시뮬레이션을 이용하여 검증 및 분석하였다.

• 한국통신학회논문지
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• 제34권11C호
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• pp.1059-1066
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• 2009

In this paper, we propose the precoder with superimposed pilots for orthogonal frequency-division multiple access (OFDMA) systems in order to enhance the transmission efficiency of the system and reduce peak-to-average power ratio (PAPR) which is the problem in OFDMA uplink. In wireless communication systems, the way to improve transmission efficiency is 1) to reduce bit error rate (BER) or 2) to increase data rate. In the proposed scheme, we design the precoder and superimposed pilots in the transmitter and use them in the receiver for increasing data rate, caused by the saved transmission bandwidth thanks to the superimposed pilots. In addition, we improve BER performance with the help of the frequency diversity gain caused by precoding. Also using superimposed pilots, we enhance the PAPR performance by increasing the average output power of the signal.

• Journal of Biosystems Engineering
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• 제36권6호
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• pp.422-433
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• 2011

Market demand for hydro-mechanical transmission (HMT) for agricultural tractors has increased recently. To select a type of HMT satisfying design conditions, performance characteristics of 12 HMT types must be understood. This study was conducted to provide tractor engineers with a guideline to select the most appropriate HMT type for their design requirements. Characteristics on speed reduction ratio, power transmission efficiency, power regeneration, lock-up angular velocity, output torque ratio and torque ratio of planetary gear train axis of the 12 HMT types were investigated and presented as either formula or graphical forms. A guideline to select proper HMT type was also presented using 2 parameter: lock-up angular velocity (${\omega}_L$) and torque ratio of the planetary gear train axis. In addition, effect of gear ratio of the planetary gear train on the power transmission efficiency was investigated and a guideline to select the best gear ratio was also presented.