• Journal of the Korean Society of Radiology
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• v.15 no.5
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• pp.705-713
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• 2021

The modulation transfer function (MTF) is calculated to analyze the resolution of the spatial frequency of the image acquired from the x-ray imaging system. In general, the response function of the detector acquires a line spread function (LSF) using a slit-camera, and derives a modulation transfer function through a Fourier transform. Because of the fact that the x-ray must always be incident on the center of the slit-camera, the tilt of the detector and slit-camera caused by the experimenter will affect the detector performance. In addition, if the tilt increases, the performance evaluation of the x-ray image system will be problematic. In this study, we analyzed the experimental and analytical models in the modulation transfer function, ie, the Fourier domain, based on the experimental error and analyzed the effect on the spatial frequency. Furthermore, performance evaluation is being carried out for various x-ray imaging systems, and experimental errors are indispensable, and the extent to which they can be tolerated should be reviewed.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.12
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• pp.43-52
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• 1999

We propose a new method for tuning of center wavelength in photorefractive filter using $LiNbO_3$ crystal doped with 0.015Wt.% Fe. through the filter bandwidth property analysis using the geometrical method, a new wavelength selectivity theory was presented. In this scheme, the tuning of the center wavelength can be achieved by the real time incident angle control of the received heam, which was gotten by the spatial light modulator. So, tuning time depend on the response time of the SLM and results in the high speed turing. Because the use of thermally fixed grating in our filter, it has uniform diffraction property to the all filtering wavelength. Designed tunable filter has 4nm bandwidth and composed of the three channel with 10nm space. From the optical experiment, we get the 4.5nm, 4.25nm, 4nm bandwidth and 1530.5nm, 1540.5nm, 1549.5nm center wavelength respectively.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2020.07a
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• pp.557-560
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• 2020

최근, 광소자에서 공간 변조되는 wavefront profile 특성을 광소자의 표면 단차 변화 없이 단일 두께 박막 상에서 자유로이 구현할 수 있는 기하위상 홀로그램 (geometric phase hologram) 기반의 optical component에 대한 관심이 증대되고 있다. 특히 이를 이용해 제작된 기하위상 렌즈 (geometric phase lens)는 dynamic phase의 공간적 차이에 의해 구현되던 기존 bulk optics 기반의 lens 대비 초박형으로 제작이 가능한 파장 선택적 flat optics 기술로써, 다초점 및 경량화를 요구하는 차세대 디스플레이 기술 (augmented reality 또는 AR, mixed reality 또는 MR) 및 광파변조 및 제어를 요구하는 홀로그래픽 카메라 분야에 대한 응용처로 많은 주목을 받고 있다. 이에 본 논문에서는 해당 기하 위상렌즈에 대한 원리 및 이에 따른 개발이슈 및 해결법에 대해 연구 하였으며, 이에 대한 응용처로 기하위상 렌즈의 편광에 따른 이중초점특성을 이용해, 기존 단일 초점 형성이 가능한 AR기기 대비, 다초점 형성이 가능한 switchable dual-depth 3D AR device를 compact한 모듈과 함께 구현하였다. 또한, 기하위상렌즈의 광파 변조 및 분리특성을 이용한 기하위상 렌즈기반의 자가간섭 홀로그래픽 시스템(GP-self-interference incoherent digital holographic, GP-SIDH)에 편광 이미지센서 적용과 함께 맞춤형 설계/제작된 기하 위상렌즈를 적용함으로써, 기존 GP-SIDH 시스템대비 안정적으로 실시간 복소 홀로그램 획득이 가능한 실시간 공간영상정보 획득용 GP-SIDH을 동영상 프레임으로 구현하였다.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.413-416
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• 2000

본논문에서는 유도전동기 속도 및 토크 제어시 고조파의 왜형률을 감소시키고 디지털 구현이 용이하며 선형제어 영역을 증가시킬 수 있는 스위칭 방식으로 Space voltage Vector PWM(Pulse Width Modulation) 설명하였으며 시뮬레이션하기 위한 user_tool로써 Matlab/Simulink를 이용하여 SVPWM을 구현하는 방법을 설명하였다 결과적으로 개루프 운전 시 유도기에 인가되는 기준전압을 각각 비과변조와 과변조 시 전압비율 변경방식을 사용하여 나타나는 응답으로 가상스위칭 시간 T1, T2, T0 와 속도, 상전류, 토크응답을 알아보았다.

• Korean Journal of Optics and Photonics
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• v.25 no.2
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• pp.85-89
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• 2014

In this paper, we present a speckle-free digital hologram with conversion to an off-axis horizontal-parallax-only (HPO) hologram. First, we record the speckle-free hologram using optical scanning holography. Second, we digitally convert the full-parallax hologram to a horizontal-parallax-only hologram. Third, we convert the horizontal-parallax-only hologram to an off-axis hologram. Finally, we show that the off-axis HPO hologram can be numerically reconstructed in space.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.8-17
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• 1999

In this paper, a proposal for improving the performance of IF in-phase combiner is presented in view of simple hardware design and good performance for space diversity application. By adding the stable normalization circuit to the phase detector, better performances are obtained even for a severe notch depth of 30 dB. To check the validity of this proposal, various results based upon numerical simulation and laboratory test are presented here in conjunction with 64-QAM digital radio relay system.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.1
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• pp.13-18
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• 1999

This paper proposes a new overmodulation stategy to give a better voltage by the full utilization of the hexagon voltage range in the space vector PWM(SVPWM) inverter. This overmodulation strategy can apply to the vector control, leading to better output torque capability in the ac motor drive system. This strategy is that in the overmodulation range, the d-axis output current is given a priority to regulate the flux well, instead the q-axis output curent is sacrificed. Therefore, the vector control even in the overmodulation PWM operation can be achieved well. For this purpose, the d-axis output voltage of a current controller to control the flux is conserved. the q-axis output voltage to control the torque is controlled to place the reference voltage vector on the hexagon boundary in case of the overmodulation. The validity of the proposed overall scheme is confirmed by simulation and experiments for a 22[kW] induction motor drive system

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.194-195
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• 2016

본 논문에서는 고효율의 3상 3레그 3레벨 정류기의 하나인 비엔나 컨버터에서 단일 반송파 비교를 이용한 새로운 공간전압벡터 펄스폭변조(SVPWM) 방식의 구현에 대해서 제안을 한다. 기존 방식들은 2개의 반송파 비교를 주로 사용하고 있거나, 변조할 전압지령 신호의 절대값을 취하여 단일 반송파 비교를 사용하고 있으나, 제안하는 방식은 전압지령 신호의 변조구간에 따른 이동과 단일 반송파 비교를 이용을 해서 2개의 반송파 비교를 사용한 방식과 동일한 특성을 나타내면서 구현이 좀 더 용이한 장점을 갖는다. 제안하는 새로운 방식에 대한 이론적인 설명과 시뮬레이션 및 실험 결과들을 제시함을 통해 제안하는 본 방식의 타당함과 성능의 우수함을 나타내고자 한다.

• Korean Journal of Optics and Photonics
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• v.33 no.6
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• pp.310-316
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• 2022

In this paper, the difference in modulation transfer function (MTF) results according to the change in the angle of a slant target when measuring a presampled MTF was confirmed, and the difference was reduced by fitting the edge spread function graph obtained to reduce the error by the target's rotation. Due to the feature of the presampled MTF method, the spatial frequency changed due to the sensor's projected intensity being changed by the target's rotation, and it was confirmed that the difference in the MTF value occurred depending on the rotation angle of the target. In this paper, the MTF was calculated after fitting only one column of the acquired image. It was confirmed that the rotation error is smaller compared to the case of the presampled MTF method and this fitting method can be applied to a scene that contains various target angles, such as auto-focusing using the MTF.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.7
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• pp.742-752
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• 1992

In this paper, a space vector concept is generalized for PWM(pulse-width modulated) inverters and PWM rectifiers with current link and voltage link respectively. Through representing three-phase variables as a space vector, we propose space vector modulations for PWM voltage and current source inverters, and PWM rectifiers with current link and voltage link. For these types, switching states of the switches are systematically analyzed from tables. It is shown in three-phase PWM rectifiers that power factor of the line current and output dc voltage can be controlled arbitrarily. The PWM rectifier with current link is also given as an example system.