• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.28.2-28.2
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• 2009

이 논문에서는 미소진동이 인공위성 영상품질에 끼치는 영향에 대해 살펴본다. 지구관측위성은 임무수행 시 영상의 지상전달 등을 위해 다양한 구동장치를 가동하며, 이로 인해 미소진동에 노출된다. 이러한 미소진동은 광학탑재체를 가진하여 초점면(Focal Plane)상의 영상운동을 야기하며, 이로 인해 영상품질이 저하된다. 특히, 고해상도 관측위성일수록 미소진동에 의한 영상품질의 저하가 커지므로, 위성개발 시에 영상품질에 대한 영향평가는 필수적이다. 이를 해석하기 위해서 키슬러플랫폼 위에서 진동원의 가진력을 측정 및 그 동특성을 분석한다. 이 가진원은 임무수행형상의 유한요소모델에 적용하여 광학탑재체 초점면의 영상운동을 계산하며, 최종적으로 영상품질에 미치는 영향을 평가한다.

• KIPS Transactions on Software and Data Engineering
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• v.6 no.1
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• pp.23-28
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• 2017

Shape from focus (SFF) is a technique used to reconstruct 3D shape of objects from a sequence of images obtained at different focus settings of the lens. In this paper, a new shape from focus method for 3D reconstruction of microscopic objects is described, which is based on gradient operator in Mathematical Morphology. Conventionally, in SFF methods, a single focus measure is used for measuring the focus quality. Due to the complex shape and texture of microscopic objects, single measure based operators are not sufficient, so we propose morphological operators with multi-structuring elements for computing the focus values. Finally, an optimal focus measure is obtained by combining the response of all focus measures. The experimental results showed that the proposed algorithm has provided more accurate depth maps than the existing methods in terms of three-dimensional shape recovery.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.349-349
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• 2011

탄소나노튜브의 전자방출 특성을 활용하면 저전압으로 냉전자를 빠른 스위칭 속도로 전자를 용이하게 제어가 가능하다. 이로 인한 고성능 엑스선 소스를 이용하여 의료영상진단과 보안검색 분야에서 많이 사용될 것으로 예상이 된다. 본 연구에서는 고성능 탄소나노튜브 기반 엑스선의 미소초점 형성을 위한 전자 방출 시뮬레이션을 실시하였다. 3극관(애노드, 게이트, 캐소드)에서 2개의 포커싱 전극을 추가한 5극선관의 전자방출 궤적에 대한 시뮬레이션을 진행하였다. 3극관을 구성하여 애노드와 게이트에 일정 전압을 정해준 후, 2개의 포커싱 전극의 전압, 포커싱 전극간의 거리, 그리고 포커싱 전극의 내부직경을 조절함으로써 애노드 상에서의 전자의 초점이 작아지는 것을 알 수 있었다. 마이크로 포커스 엑스레이 소스는 의료영상진단에 있어서 고해상도 의료기기로의 응용이 가능하다.

• Journal of the Korean Vacuum Society
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• v.20 no.6
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• pp.403-408
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• 2011

To develop the MFX (Micro-Focus X-ray) tube, the trajectories of electrons emitted from the field emission cathode was simulated using SIMION program. Regardless of starting position of the electron in emitter, we found out the fact that there is the optimum extractor voltage Ve, which can focus the electron beam on one place. Extractor voltage Ve varies depending on the source voltage Vs, but the ratio of two voltages (Ve/Vs) is always constant, its value was 99.4%. When the ratio of two voltages (Ve/Vs) was 99.4%, the beam diameter in the cross-over point was $1.2{\mu}m$. Because the focal spot size in MFXG (Micro-Focus X-ray Generator) can not be less than the cross-over diameter within MFX tube, it is important to find out the conditions that can make a smaller beam diameter. Therefore, the above results is considered to be a very important ones in the development of the MFXG.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.757-764
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• 2015

Mathematical modeling of focal plane compensation device in the small earth-observation satellite camera has been conducted experimently for compensation of micro-vibration disturbance. The PZT actuators are used as control actuators for compensation device. It is quite difficult to build up mathematical model because of hysteresis characteristic of PZT actuators. Therefore, the compensation device system is assumed as a $2^{nd}$ order linear system and modeled by using MATLAB System Identification Toolbox. It has been found that four linear models of compensation device are needed to meet 10% error in the input frequency range of 0~50Hz. These models describe accurately the dynamics of compensation device in the 4 divided domains of the input frequency range of 0~50Hz, respectively. Micro-vibration disturbance can be compensated by feedback control strategy of switching four models appropriately according to the input frequency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.73-76
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• 2010

The issue of inspection and characterization of microstructures has emerged as a major consideration in design, fabrication, and detection of MEMS devices. However, the conventional measurement techniques, including scanning electron microscopy (SEM) imaging, atomic force microscopy (AFM) scanning, and mechanical surface profiler, require often destructive process or may be difficult to measure with a wafer scale. In this paper, we characterize the surface profiles of microstructures using an optical scanner based on a DVD pick-up module. Scanning images of the microstructures are successfully generated using the intensity of reflected light from different depths of the surface profiles, based on the focus error signal (FES) from photodiodes. It is shown that the proposed optical scanner can be used as an alternative measurement system with high performance and low cost, compared to conventional measurement techniques.

• The Journal of Engineering Geology
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• v.20 no.4
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• pp.461-465
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• 2010

Weathering and permeability in rocks play a very important role in underground disposal of radioactive waste and their long-term management as well as stability security of rock structures. Weathering and permeability of rocks are largely controlled by the characters of inner structures of rocks. In other words, weathering rate can be accelerated depending on the quantity of pore and microcrack in rocks. Quantitative evaluation of inner structures of rocks can serve as a tool that can assess the degree of weathering of rocks. Therefore it can be said that the understanding of three dimensional distribution of the inner structure of rocks is important for long-term management of rock structures. This study was performed to analyze three dimensional distribution of pore in rocks using Micro Focus X-ray CT on fresh granite and weathered granite from Korea. Results of the analysis clearly show distribution of pore and porosity of the inner rock.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.7
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• pp.575-582
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• 2018

The spaceborne cooler is applied to cool down of the focal plane of the infrared detector of the observation satellite. However, this cooler induces unnecessary micro-jitter which can degrade the image quality of the high-resolution observation satellite. In this study, we proposed a multi-layered blade type vibration isolator to attenuate micro-vibration generated from a spaceborne cooler, while assuring structural safety of the cooler under severe launch loads without an additional launch-lock device. The blade of the isolator is formed with multi-layers in order to obtain durability against fatigue failure and an adhesive is applied between each layers for granting high damping capability under launch vibration environment. In this study, the basic characteristics of the isolator were measured using the free-vibration test. The effectiveness of the isolator design was demonstrated by launch vibration test at qualification level.

• The Journal of the Acoustical Society of Korea
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• v.38 no.6
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• pp.687-696
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• 2019

Conventional feature of seismic classification focuses on strong seismic classification, while it is not suitable for classifying micro-seismic waves. We propose a feature extraction method based on histogram and Principal Component Analysis (PCA) in frequency-time space suitable for classifying seismic waves including strong, micro, and artificial seismic waves, as well as noise classification. The proposed method essentially employs histogram and PCA based features by concatenating the frequency and time information for binary classification which consist strong-micro-artificial/noise and micro/noise and micro/artificial seismic waves. Based on the recent earthquake data from 2017 to 2018, effectiveness of the proposed feature extraction method is demonstrated by comparing it with existing methods.

• Korean Journal of Optics and Photonics
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• v.13 no.2
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• pp.117-122
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• 2002

Some 10$\times$10 micro-lens arrays of a period of 300 ${\mu}{\textrm}{m}$, a thickness of 17 ${\mu}{\textrm}{m}$, and a focal length of 2.2 mm are fabricated by exposing a thick layer of photoresist through a grayscale mask via UV proximity printing. The grayscale mask is fabricated in a holographic film by reducing (6.6X) a high-resolution black-and-white film where a grayscale patters of a micro-lens array designed by a computer has been written using a film recorder. The proposed method has the advantage of a low fabrication cost, a fill-factor of almost 100% and the ease of realizing an aspheric lens.