• 한국위성정보통신학회논문지
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• 제3권2호
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• pp.38-42
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• 2008

2005년 DVB-S2 규격이 최종 마무리 되었지만 이미 보급된 기존의 수많은 DVB-S 수신기는 새로이 완전한 DVB-S2 수신기로 교체되기까지는 여전히 DVB-S 신호는 수신되어야 한다. 이를 위해서 방송사업자는 기존의 DVB-S 수신기에는 DVB-S 신호를, DVB-S2 수신기에는 DVB-S2 신호를 전송해야 한다. DVB-S2 수신기에서 DVB-S서비스를 수용하기 위해서는 DVB-S2 chip에 DVB-S 모듈이 구현되어야 한다. 이런 역호환성을 위해서 시스템에서는 계층적 변조 방식을 적용해야 하며, 시스템 마진을 만족하기 위해 본 논문에서는 편향각에 따른 시스템의 성능을 분석하였으며 또한 성능을 검증해 보았다. 그리고 본 방식을 검증하기 위해서 FPGA chip을 이용하여 테스트베드를 구현하였으며 이를 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권12호
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• pp.6190-6213
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• 2019

For small-scale vector data, restrictions on watermark scheme capacity and robustness limit the use of copyright protection. A watermarking scheme based on robust geometric features and capacity maximization strategy that simultaneously improves capacity and robustness is presented in this paper. The distance ratio and angle of adjacent vertices are chosen as the watermark domain due to their resistance to vertex and geometric attacks. Regarding watermark embedding and extraction, a capacity-improved strategy based on quantization index modulation, which divides more intervals to carry sufficient watermark bits, is proposed. By considering the error tolerance of the vector map and the numerical accuracy, the optimization of the capacity-improved strategy is studied to maximize the embedded watermark bits for each vertex. The experimental results demonstrated that the map distortion caused by watermarks is small and much lower than the map tolerance. Additionally, the proposed scheme can embed a copyright image of 1024 bits into vector data of 150 vertices, which reaches capacity at approximately 14 bits/vertex, and shows prominent robustness against vertex and geometric attacks for small-scale vector data.

• Journal of Information Display
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• 제5권1호
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• pp.22-27
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• 2004

Photopolymers are quite promising candidates for holographic data storage and diffusers because of their high sensitivity and high refractive index modulation. New photopolymers were prepared using the cellulose ester binder bearing different kinds of monomer. The holographic gratings were elaborated successfully in these photopolymer samples by conventional optical interference method. We investigated the dynamic behavior of the diffraction efficiency and the effect of the functionality of the monomer doped into the polymer binder. Triacrylate monomer doped photopolymer showed the highest diffraction efficiency of around 80-90 %, even under low intensity of writing beam (I=2 mW/$cm^2$). We inscribed the gratings of the glass diffuser on the surface of the photopolymer and investigated their diffusion properties.

• 대한전자공학회논문지
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• 제27권4호
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• pp.534-540
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• 1990

In this paper the characteristics of submicron gate GaAs MESFET's have been studied using a particle model which takes into account the hot-electron transport phenomena, i.e., the velocity overshoot. \ulcornervalley(<000> direction), L valley (<111>direction), X valley (<100>direction) as the GaAs conduction energy band and optical phonon, acoustic phonon, equivalent intervalley, nonequivalent intervalley scattering as the scattering models, have been considered in this simulation. And the GaAs material and the device simulation have been done by determination of the free flight time, scattering mechanism and scattering angle according to Monte-Carlo algorithm which makes use of a particle model. As a result of the particle simulation, firstly the electron distribution, the potential energy distribution and the situation of electron displacement in 0.6 \ulcorner gate length device have been obtained. Secondly, the cutoff frequency, obtained by this method, is k47GHz which is in good agreement with the calculated result of theory. And the current-voltage characteristics curve which takes account of the buffer layer effect has been obtained. Lastly it has been verified that parasitic current at the buffer layer can be analyzed using channel depth modulation.

• Journal of the Optical Society of Korea
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• 제19권5호
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• pp.487-493
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• 2015

A wavefront coding (WFC) technique provides an extension of the depth of field for a microscopy imaging system with slight loss of image spatial resolution. Through the analysis of the relationship between the incidence angle of light at the phase mask and the system pupil function, a mixing symmetrical cubic phase mask (CPM) applied to 5X-40X micro-objectives is optimized simultaneously based on point-spread function (PSF) invariance and nonzero mean values of the modulation transfer function (MTF) near the spatial cut-off frequency. Optimization results of the CPM show that the depth of field of these micro-objectives is extended 3-10 times respectively while keeping their resolution. Further imaging simulations also prove its ability in enhancing the defocus imaging.

• 전력전자학회논문지
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• 제20권5호
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• pp.402-409
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• 2015

This paper proposes a novel rotor position error calculation method for high-frequency signal-injected sensorless control. The rotor position error using the conventional modulation method can be only measured up to ${\pm}45^{\circ}$. In addition, when the rotor position estimation error is not sufficiently small, the small angle approximation in no longer valid. To overcome these problems, this study introduces a new rotor position error calculation method using the rotating matrix. In this study, the position error measurement range of the proposed method is extended from ${\pm}45^{\circ}$ to ${\pm}90^{\circ}$. The linearity between the real rotor position error and the estimated error is maintained by nearly $90^{\circ}$. These features of the proposed method improve the performance of the sensorless control. The validity of the proposed method is verified by simulations and experiments.

• 대한기계학회논문집B
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• 제25권3호
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• pp.296-304
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• 2001

A new method of measuring the thermal diffusivity of solid material at room temperature using photothermal displacement is proposed. The influence of the parameters, such as radius and modulation frequency of the pump beam and the sample thickness, was studied. From the minimum position of phase of measured deflection with respect to the pump beam, the thermal diffusivity of the materials can be obtained. The position where phase has the minimum value is determined using multiparameter least-square regression fitting. The experimental values for different samples obtained by applying the new method are in good agreement with the literature values.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1528-1538
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• 2018

In this paper, configuration of $1-{\phi}$ seven-level boost DC-link cascade based reversing voltage multilevel inverter (BDCLCRV MLI) is proposed for uninterrupted power supply (UPS) applications. It consists of three level boost converter, level generation unit and full bridge circuit for polarity generation. When compared with conventional boost cascaded H-bridge MLI configurations, the proposed system results in reduction of DC sources, reduced power switches and gate drive requirements. Inverter switching is accomplished by providing appropriate switching angles that is generated by any optimization switching angle techniques. Here, round modulation control (RMC) method is taken as the optimization method and switching angles are derived and the same is compared with various switching angles methods i.e., equal-phase (EP) method, and half-equal-phase (HEP) method which results in improved quality of obtained AC power with lowest total harmonic distortion (THD). Reduction in DC sources and switch count makes the system more cost effective. A simulation and prototype model of $1-{\phi}$ seven-level BDCLCRV MLI system is developed and its performance is analyzed for various operating conditions.

• 한국추진공학회지
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• 제15권3호
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• pp.22-30
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• 2011

추력변화를 위한 방법에는 여러 가지가 있는데, 고압력 강하 시스템, 이중 매니폴드 분사기, 가스 분사, 다중 챔버, 펄스 추력, 움직이는 분사기 구성요소 등이 있다. 이 중에서 이중 매니폴드 분사기의 경우에는 하나의 분사기 구조에 서로 다른 두 개의 매니폴드를 가지는 분사기를 결합하는 방식의 분사기인데, 각 분사기는 각각의 연료 공급시스템을 독립적으로 가지고 있어 각 매니폴드마다 독립적으로 유량을 조절 할 수 있다. 본 논문에서는 이중 매니폴드 분사기를 사용하여 넓은 추력범위에서 연료분사의 안정성을 판단하기 위하여 각 매니폴드의 접선방향 유입구 넓이의 비와 분사압력에 따라 분사 형상을 측정하고, 분사기 오리피스 끝단에서 액막 두께를 측정하였다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2016년도 추계학술대회
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• pp.652-654
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• 2016

본 논문에서는 FPGA를 활용하여 SVPWM (Space Vector Pulse Width Modulation)방식의 정현파 BLDC 모터 구동 로직을 설계 및 구현하였다. Hall sensor를 이용한 BLDC 모터 구동 회로는 정현파 PWM 생성회로, 데드타임 회로 및 리드 앵글 생성 회로 등으로 구성 된다. 특히 PWM 생성 회로는 SVPWM방식을 이용하여 기존 정현파 PWM 대비 선형구간이 15.5% 증가된다. 설계한 회로는 VHDL을 이용하여 모의실험 하였으며 Xilinx Spartan-6 FPGA보드를 통하여 회로의 동작 및 성능을 검증하였다. 검증 결과 모터구동 전류의 THD (Total Harmonic Distortion)은 19.32% 로 기존 정현파 구동 회로 대비 우수한 특성을 보였으며 회전자 분해능은 $1.6^{\circ}$로 정밀 제어가 가능함을 확인하였다.