• 전력전자학회:학술대회논문집
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• 전력전자학회 2020년도 전력전자학술대회
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• pp.261-262
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• 2020

본 논문은 DC/DC 위상천이 풀브릿지 컨버터의 과도상태 개선을 위한 듀얼모드 제어를 제안한다. 기존의 discontinuous conduction mode (DCM)과 continuous conduction mode (CCM)을 이용하여 운용하는 위상천이 풀브릿지 컨버터는 각 모드의 상이한 전압게인의 특성을 고려하지 않아 급격한 로드 변동시 출력 전압의 언더슈트 혹은 오버슈트가 크게 발생한다. 제안하는 듀얼모드 제어는 DCM과 CCM 각 모드 별개로 제어가 적용되고 출력 전류의 변화에 대응하는 적응형 feed-forward 제어가 적용되어 컨버터의 과도상태를 개선할 수 있다. 듀얼모드의 제어 방법의 성능과 타당성을 시뮬레이션을 통해 입증한다.

• 대한기계학회논문집A
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• 제24권10호
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• pp.2477-2486
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• 2000

A planetary gear assembly is a key component to combine and/or split a power from the source. With a planetary gear assembly, a continuously variable unit extends its capacity by means of power bra nching mechanism. Power branching with one planetary gear assembly and one continuously variable unit is categorized into 12 basic types. Each type represents peculiar power transmitting characteristics. Additionally, a multi-mode (range) continuously variable transmission can be designed with accompanying clutches. A multi-mode continuously variable transmission changes the path through which the source power is transmitted. Each path has its own features, such as high efficiency. In this paper, some design principles are examined such as, criteria to guarantee the minimum power efficiency, and constraints to guarantee the smooth mode shift after discussing well-known features of multi-mode M mathematically.

• 한국통신학회논문지
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• 제19권8호
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• pp.1548-1557
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• 1994

본 논문에서는 CPM(continuous phase modulation) 변조방식에 연집 에러 검출및 최대 확률론적 복호방식으로 구성된 연집에러 정정을 위한 이중모드 적응 복호 알고리듬을 제시한다. 이중모드(dual mode) 적응 복호기는 비터비 복호기로 동작하다가, 비터비 복호기에 의해 정정될 수 없는 에러가 검출될 경우 연집 에러 정정모드로 전환되어 복호가 수행된다. 페이딩 채널에서 이중모드 적응 복호 알고리듬과 인터리빙 방식이 같은 메모리의 양을 사용했을 때에, 이중모드 적응 복호기의 성능이 인터리빙을 사용했을 때의 성능 보다 우수함을 알 수 있다. 본 논문의 실험 결과에서 얻어진 성능 향상의 이점 이외에도 이중모드 적응복호 알고리듬을 사용하면 인터리빙 방법을 사용할 때에 발생되는 긴 시간지연의 문제점도 극복할 수 있다.

• 한국광학회지
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• 제14권3호
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• pp.292-297
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• 2003

최대 1.9 W의 레이저 다이오드 출력을 Nd:YV $O_4$결정 단면에 집속시키고 공진기 내부에 KTP 결정을 두어서 제2고조파 변환시켜 녹색광(532 nm) 레이저를 발생시켰다. 다이오드 레이저 스퍽트럼과 레이저 결정의 흡수 스펙트럼을 비교하여 최적의 다이오드 작동 온도를 찾았다. 공진기 길이와 출력경의 곡률을 변화시키면서 출력의 변화를 관측한 결과, 최대 80 ㎽의 녹색광 레이저 출력을 얻었으며 최대 출력을 내는 공진기 조건에서는 집속된 여기광의 직경과 TE $M_{00}$ 모드의 직경이 일치함을 알았다. 발생된 녹색광 레이저는 다중모드로 발진하였으며 출력 요동이 심하였다. 단일모드 발진을 시키기 위하여 브루스터 판과 에탈론 등을 사용하는 여러 가지 형태의 공진기를 시도하여 보았다. 실험 결과, 에탈론을 사용한 공진기에서 가장 큰 출력인 60 ㎽ 의 단일 종모드 출력을 얻었다. 단일모드로 발진하는 레이저의 출력 요동은 다중 모드에 비하여 1/10이하로 감소하였다.

• 한국전자파학회논문지
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• 제25권3호
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• pp.296-303
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• 2014

본 논문에서는 제한된 위치에서 측정된 수신 신호 세기(RSSI) 값과 3차원 지리 정보를 기반으로 주변의 전파 환경을 추정하고, 시각화할 수 있는 알고리즘을 제안한다. RSSI가 동일한 수신점은 송신점으로부터 같은 거리에 위치한다는 가정 하에서 삼각형의 외심을 이용하여 송신점의 위치를 추정하고, 전파 모델을 이용해 전파 손실을 고려하여 전파환경을 시각화한다. 영상 신호 처리에서 사용되는 모드 탐색 알고리즘인 mean-shift clustering 방법을 사용하여 피크 값을 탐색하고, 여러 개의 추정점들의 무게 중심을 사용하여 오차를 감소시킬 수 있는 방법을 제안한다. 본 논문에서 제시한 모드 탐색 알고리즘을 이용한 전파 환경 시각화 기법은 전파 자원의 효율적인 이용을 위한 전파 감시 시스템에 활용될 수 있을 것으로 기대된다.

• Journal of Biosystems Engineering
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• 제36권1호
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• pp.23-32
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• 2011

In this work, the finite element method was used to investigate the shifts of resonance frequencies and quality factor of whispering-gallery-mode (WGM) for an opto-fluidic ring resonator (OFRR) biosensor. To describe the near-field radiation transfer, the time-domain Maxwell's equations were employed and solved by using the in-plane TE wave application mode of the COMSOL Multiphysics with RF module. The OFRR biosensor model under current study includes a glass capillary with a diameter of 100 mm and wall thickness of 3.0 mm. The resonance energy spectrum curves in the wavelength range from 1545 nm to 1560 nm were examined under different biosensing conditions. We mainly studied the sensitivity of resonance shifts affected by changes in the effective thickness of the sensor resonator ring with a 3.0 mm thick wall, as well as changes in the refractive index (RI) of the medium inside ring resonators with both 2.5 mm and 3.0 mm thick walls. In the bulk RI detection, a sensitivity of 23.1 nm/refractive index units (RIU) is achieved for a 2.5 mm thick ring. In small molecule detection, a sensitivity of 26.4 pm/nm is achieved with a maximum Q-factor of $6.3{\times}10^3$. These results compare favorably with those obtained by other researchers.

• Current Optics and Photonics
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• 제1권2호
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• pp.157-162
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• 2017

In large liquid crystal displays, the image quality in an oblique viewing direction is a crucial issue. From this perspective, 8-domain polymer-stabilized vertical alignment (PS-VA) mode has been developed to suppress the color shift in oblique viewing directions, compared to that in 4-domain PS-VA mode. To realize the 8-domain PS-VA, the four domains in a pixel are each divided into two regions, such that applying different electric potentials result in different tilt angles in these two regions, while keeping four azimuthal directions in each domain. However, applying different voltages in a pixel causes drawbacks, such as requiring additional processes to construct a capacitor and a transistor, which will further reduce the aperture ratio. Here we propose a different approach to form the 8-domain, by controlling surface polar anchoring energy and the width of patterned electrodes in two regions of a pixel. As a result, the gamma-distortion index (GDI), measured at an azimuthal angle of $0^{\circ}$, is reduced by about 23% and 8%, compared to that of a conventional 4-domain at polar angles of $30^{\circ}$ and $60^{\circ}$ respectively.

• 전력전자학회논문지
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• 제23권3호
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• pp.190-198
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• 2018

This paper proposes a nonisolated, bidirectional, soft-switching DC - DC converter with PWM plus phase shift (PPS) control. The proposed converter has an input-parallel/output-series configuration and can achieve the interleaving effect and high voltage gains, resulting in decreased voltage ratings in all related devices. The proposed converter can operate under zero-voltage switching (ZVS) conditions for all switches in continuous conduction mode. The power flow of the proposed converter can be controlled by changing the phase shift angle, and the duty is controlled to balance the voltage of four high voltage side capacitors. The PPS control device of the proposed converter is simple in structure and presents symmetrical switching patterns under a bidirectional power flow. The PPS control also ensures ZVS during charging and discharging at all loads and equalizes the voltage ratings of the output capacitors and switches. To verify the validity of the proposed converter, an experimental investigation of a 2 kW prototype is performed in both charging and discharging modes under different load conditions and a bidirectional power flow.

• 한국정밀공학회지
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• 제25권3호
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• pp.93-100
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• 2008

Laser interferometry is widely used as a measuring system in many fields because of its high resolution and ability to measure a broad area in real-time all at once. In conventional LASER interferometry, for example Out-of-plane ESPI(Electronic Speckle Pattern Interferometry), In plane ESPI, Shearography and Holography, it uses PZT or other components as a phase shift instrumentation to extract 3D deformation data, vibration mode and others. However, in most cases PZT has some disadvantages, which include nonlinear errors and limited time of use. In the present study, a new type of LASER interferometry using a laser diode is proposed. Using LASER Diode Sinusoidal Phase Modulating (LD-SPM) interferometry, the phase modulation can be directly modulated by controlling the LASER Diode injection current thereby eliminating the need for PZT and its components. This makes the interferometry more compact. This paper reports on a new approach to the LD Modulating interferometry that involves four-buckets phase shift method. This study proposes a four-bucket phase mapping algorithm, which was developed to have a guaranteed application, to stabilize the system in the field and to be a user-friendly GUI. In this paper, the theory for LD wavelength modulation and sinusoidal phase modulation of LD modulating interferometry is shown. Four-bucket phase mapping algorithm is then introduced.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.843-846
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• 2004

Cavity tone is generated due to the feedback between flow and acoustic wave. It is recognized that the period is determined by the time required for the flow convection in one direction, the time required for the acoustic propagation in the other direction and the time for phase shift depending on the flows and mode. Most of the phenomena have been investigated by experiments and a simple but fundamental theory. But the cause of the phase shift and the correctness of the theory have not been clearly explained so far. In this paper, the phenomena are calculated numerically to obtain detail information of flow and acoustic wave to explain the mechanism including the phase. High order high resolution scheme of optimized high order compact is used to resolve the small acoustic quantities and large flow quantities at the same time. The data are reduced using cross correlation function in space and time and cross spectral density function which has phase information. Abrupt change in pressure near corner in cavity is observed and is relate to phase variation. The time required for the feedback between the flow and acoustic wave is calculated after the numerical simulation f3r various modes. The periods based on the time calculated using the above method and direct observation from the acoustic waves generated and propagated in the numerical simulation are compared. It is found that no phase shift is required if we examine the time required carefully. Rossiter's formula for the cavity tone used for quick estimation needs to be modified far some modes.