• ETRI Journal
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• 제39권3호
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• pp.390-397
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• 2017

In this paper, we propose a scheme for designing a tunable pixel layer based on a $Ge_2Sb_2Te_5$ (GST) alloy thin film. We show that the phase change of GST can significantly affect the reflection characteristic when the GST film is embedded into a dielectric encapsulation layer. We investigate the appropriate positions of the GST film within the dielectric layer for high diffraction efficiency, and we prove that they are antinodes of Fabry-Perot resonance inside the dielectric layer. Using the proposed scheme, we can increase the diffraction efficiency by about ten times compared to a bare GST film pixel, and 80 times for the first-to-zeroth-order diffraction power ratio. We show that the proposed scheme can be designed alternatively for a broadband or wavelength-selective type by tuning the dielectric thickness, and we discuss a multi-phase example with a double-stack structure.

• 한국전자파학회논문지
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• 제22권9호
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• pp.820-826
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• 2011

본 논문에서는 자기 공명 방식의 무선 전력 전송 시스템에서 효율 향상 방안을 제시하였다. 공진 코일은 헬리컬과 스파이럴 형태가 결합된 구조를 제안하였으며, 소스와 디바이스 코일은 단일 원형 루프 형태로 설계하였다. 측정 결과, 송수전 코일이 120 mm의 거리로 이격되어 있을 때 헬리컬과 스파이럴 구조를 결합한 공진기는 기존의 헬리컬 구조의 공진기보다 효율이 13 % 향상되는 결과를 보였다. 뿐만 아니라, 크기도 기존 공진기에 비해 33 % 소형화할 수 있었다.

• 한국전자파학회논문지
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• 제21권10호
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• pp.1103-1108
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• 2010

본 논문에서는 PIFA의 급전점과 단락점을 둘러싸는 급전 루프 내부에 커패시터 구조를 삽입하는 새로운 타입의 4중 대역(GSM900/DCS/PCS/W-CDMA) PIFA 설계를 제안한다. 커패시터의 삽입을 통해서 병렬 공진점인 2.01 GHz에서의 반사 계수 -2.73 dB를 -6.26 dB로 낮추는 효과를 얻을 수 있었다. 병렬 공진에서의 좋지 못한 방사 특성을 개선시킴으로써 고차 대역(DCS/PCS/W-CDMA)에서의 광대역 특성을 나타내었다.

• 한국기계가공학회지
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• 제12권5호
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• pp.16-22
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• 2013

A two-dimensional photonic crystal structure was investigated using a roll-to-roll nanoreplication and physical vapor deposition processes for the inexpensive enhanced fluorescence substrate which is not sensitive to the polarization directions of excitation light source. An 8 inch silicon master having nano dot array with a diameter of 200 nm, a height of 100 nm and a pitch of 400 nm was prepared by KrF laser scanning lithography and reactive ion etching processes. A flexible polymer mold was fabricated by flat type UV replication process and a deposition of 10 nm nickel layer as an anti-adhesion layer. A roll mold was prepared by warping the flexible polymer mold on an aluminum roll base and a roll-to-roll UV replication process was carried out using the roll mold. After the deposition of ~ 100 nm $TiO_2$ layer on the replicated nano dot array, a 2 dimensional photonic crystal structure was realized with a resonance wavelength of 635 nm for both p- and s-polarized light sources.

• 전기학회논문지P
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• 제65권2호
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• pp.114-121
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• 2016

This paper is Instant space vector PWM(Pulse Width Modulation)power conversion devices in switching power semiconductors from my generation to losses and switching when the voltage surge and current surge of electronic noise(EMI: Electro Magnetic Interference / RFI: Radio Frequency Interference)to effectively minimize the power soft-switching power conversion circuit topologies of auxiliary resonant DC tank for the purpose of high performance realization of the electric power conversion system by the high-speed switching of a semiconductor device(AQRDCT simultaneously : an active auxiliary resonance using auxiliary Quasi-resonant DC tank)DC link snubber switch has adopted a three-phase voltage inverter. AQRDCL proposed in this paper can reduce the effective and current peak stress of the power semiconductors of the auxiliary resonant snubber circuit compared to the conventional active-resonant DC link snubber, it is not necessary to install the clamp switch of the auxiliary resonant DC link, DC the peak current and power loss of the bus line can be reduced.

• 조명전기설비학회논문지
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• 제23권11호
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• pp.22-27
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• 2009

This paper presents a two-paralleled four quadrant DC chopper type PWM power conversion circuit in order to generate a gradient magnetic field in the Magnetic Resonance Imaging (MRI) system. This circuit has 8-IGBTs at their inputs/outputs to realize further high-power density, high speed current tracking control, and to get a low switching ripple amplitude in a controlled current in the Gradient Coils (GCs). Moreover, the power conversion circuit has to realize quick rise/fall response characteristics in proportion to various target currents in GCs. It is proposed in this paper that a unique control scheme can achieve the above objective DSP-based control system realize a high control facility and accuracy. It is proved that the new control system will greatly enlarge the diagnostic target and improve the image quality of MRI.

• 한국음향학회지
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• 제11권4호
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• pp.31-35
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• 1992

고출력 가솔린 엔진에서 연소실 내의 급격한 압력 변화에 의해 노킹음이 발생되는데 이로 인하여 공진현상이 일어난다. 일반적으로 이러한 공진음은 5KHz 이상에서 발생되고 이 현상에 대한 고출력 가솔린 엔진의 노킹제어 시스템을 설계하는데 매우 중요하다. 본 논문에서는 고출력으로 설계된 엔진에서 사용되는 노킹 제어시스템을 설게하기 위해 연소실에서 발생되는 노킹현상을 이론적으로 분석하여 노킹음의 모드별 공진 주파수를 예측하였다. 또한 스쿠프 알파 엔진과 독일 보슈사의 비공진형 노킹센서를 시용하여 실험을 수행하였고, 그 결과 이론과 실험이 잘 일치함을 알 수 있었다.

• Journal of Power Electronics
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• 제18권3호
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• pp.757-765
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• 2018

This paper deals with the instability and resonant phenomena in distribution systems with multiple grid-connected inverters with an LCL output filter. The penetration of roof-top and other types of small photovoltaic (PV) grid-connected systems is rapidly increasing in distribution grids due to the attractive incentives set forth by different governments. When the number of such grid-connected inverters increases, their interaction with the distribution grid may cause undesirable effects such as instability and resonance. In this paper, a grid system with several grid-connected inverters is studied. Since proportional-resonant (PR) controllers are becoming more popular, it is assumed that most inverters use this type of controller. An LCL filter is also considered at the inverters output to make the case as realistic as possible. A complete modeling of this system is presented. Consequently, it is shown that such a system is prone to instability due to the interactions of the inverter controllers. A modification of PR controllers is presented where the output capacitor is virtually decreased. As a result, the instability is avoided. Simulation results are presented and show a good agreement with the theoretical studies. Experimental results obtained on a laboratory setup show the validity of the analysis.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.204-206
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• 2002

For small capacity rectifier circuits such as these for consumer electronics and appliances. capacitor input type rectifier circuits are generally used Consequently. various harmonics generated within the power system become a serious Problem. Various studies of this effect have been presented previously. However. most of these employ switching devices, such as FETs and the like. The absence of switching devices makes systems more tolerant to over -load, and brings low radio noise benefits. We propose a power factor correction scheme using a LC resonant in commercial frequency without switching devices. In this method. It makes a sinusoidal wave by widening conduction period using the current resonance in commercial frequency. Hence, the harmonic characteristics can be significantly improved. where the lower order harmonics. such as the fifth and seventh orders are much reduced. The result are confirmed by the theoretical and expermental implementations.

• 대한족부족관절학회지
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• 제13권1호
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• pp.19-22
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• 2009

Purpose: This retrospective study was designed to determine the type and frequency of associated lesions in patients with chronic lateral ankle instability who had modified Brostrom lateral ankle ligament reconstruction. Materials and Methods: Between 2004 and 2007, 60 cases of 60 patients were enrolled in this study. A retrospective review of the magnetic resonance images of the affected ankle was conducted by two orthopedic surgeons who did not get any information about intraoperative findings and the lesions were admitted when two doctors were coincident. Results: The overall incidence of associated lesions found in this study was about 83%. Peroneal tenosynovitis was the highest frequency (32%), followed by osteochondral lesion of talus (28%), anterolateral impingement (15%), Os subfibula (13%), Os trigonum (12%), ankle synovitis (12%), anterior tibiofibular ligament tear (15%), anterior bony spur (7%). Another findings were loose bodies (5%), flexor tendon tenosynovitis (5%), medial osteophyte (3%). Conclusion: Identifying these associated lesions will be helpful in treating chronic lateral ankle instability especially when the surgeon have a plan to operate the instability. We suggest that the better results can be obtained when the associated lesions are corrected simultaneously.