• 한국광학회지
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• 제13권2호
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• pp.89-91
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• 2002

기존의 가시광선 Twyman-Green 간섭계를 이용하여 불투과 평면창의 평행도 및 상대적 표면형상 오차를 동시에 정밀하게 측정할 수 있는 새로운 방법을 제시하고, 적외선 변조전달성능(MTF) 측정장비용 필터에 대하여 시험적으로 측정한 격과를 기술하였다.

• 한국의류학회지
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• 제25권1호
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• pp.61-70
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• 2001

As important factors determining human sensorial comfort, liquid moisture management and surface properties of heat resistant workwear materials were examined. To figure out liquid moisture management properties of the test materials, absorption capacity, rate of absorption, and evaporation properties were assessed. A modified GATS(Gravimetric Absorbency Testing System) was used to measure the liquid moisture accumulation associated with the wicking of liquid moisture from sweating skin. The GATS procedure measures demand wettability of materials to take up liquid in a direction perpendicular to the fabric surface and it was modified to incorporate a special test cell and cover to assess absorption behavior in the presence of evaporation. Fabric stiffness, smoothness, number and the length of surface fibers, and an estimate of the contact area between the skin and fabric surface were measured to characterize the mechanical and surface properties of the test materials. Also an estimate of the force with which a fabric clings to moist skin was made using as wet-cling index.

• Journal of the Optical Society of Korea
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• 제18권4호
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• pp.335-340
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• 2014

Based on Zernike polynomial fitting, we propose an algorithm believed to be new for interferometric measurements of rotationally asymmetric surface deviation of optics. This method tests and calculates each angular surface by choosing specified rotation angles with lowest error. The entire figure can be obtained by superimposing these sub-surfaces. Simulation and experiment studies for verifying the proposed algorithm are presented. The results show that the accuracy of the proposed method is higher than single-rotation algorithm and almost comparable to the rotation-averaging algorithm with fewer rotation measurements. The new algorithm can achieve a balance between the efficiency and accuracy.

• 비파괴검사학회지
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• 제32권4호
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• pp.388-392
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• 2012

본 연구에서는 표면파의 음향비선형 특성 측정을 위해 선 배열 레이저 빔을 이용하여 협대역의 표면파를 발생시키고 레이저 TWM(Two-Wave Mixing) 방식으로 수신하는 완전 비접촉 측정 방법이 도입되었다. 이 기술은 알루미늄 합금의 소성변형과 음향비선형 특성과의 상관성을 조사하는데 적용되었다. 그 결과, 재료의 소성변형에 따라 음향 비선형성이 비례적으로 증가하는 것으로 나타났으며, 이는 접촉식 PZT 탐촉자 수신 방법으로 측정한 결과와 동일한 경향이다.

• 한국광학회지
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• 제34권3호
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• pp.117-123
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• 2023

반사경의 광학면이 넓어질수록 높은 공간 주파수 형상이 광학계의 성능에 큰 영향을 주므로, 대형 반사경 성능 평가에서 이를 측정할 수 있어야 한다. 따라서 높은 주파수의 형상을 샘플링할 수 있는 고해상도 형상 측정 시스템이 필요하다. 본 연구에서는 반사경의 고해상도 형상 측정을 위한 회전 프리즘 정합 간섭계(rotational prism stitching interferometer, RPSI)라는 새로운 방법을 제안한다. RPSI는 기존에 사용되고 있는 상용 간섭계에 빔 확장 렌즈, 이송 거울, 회전 프리즘 등을 추가하여 구성되었으며, 간섭계를 움직이지 않고 원통 좌표계를 기준으로 전체 구경을 아우르는 부분 구경 형상들을 측정한다. 측정된 부분 구경들은 최소자승법을 이용한 부분 구경 정합법을 이용하여 정합되며, 빔확장 렌즈 배율의 제곱만큼 높은 샘플링 밀도로 전체 구경 형상 정보를 복원 가능하다. 3배율을 가지는 RPSI를 이용하여 직경 40 mm의 구면 반사경 형상을 측정하였고, 간섭계 단독으로 측정한 전체 구경 형상과 비교 검증하였다. 약 1 nm RMS의 근소한 차이로 유사한 형상을 잘 복원할 수 있었으며, 간섭계 단독으로 사용한 형상 측정 결과보다 렌즈의 배율의 제곱배만큼 향상된 샘플링 밀도로 형상 측정이 가능함을 확인하였다.

• Journal of Astronomy and Space Sciences
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• 제27권2호
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• pp.153-160
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• 2010

We modified the optical system of 500 mm wide-field telescope of which point spread function showed an irregularity. The telescope has been operated for Near Earth Space Survey (NESS) located at Siding Spring Observatory (SSO) in Australia, and the optical system was brought back to Korea in January 2008. After performing a numerical simulation with the tested value of surface figure error of the primary mirror using optical design program, we found that the surface figure error of the mirror should be fabricated less than root mean square (RMS) $\lambda$/10 in order to obtain a stellar full width at half maximum (FWHM) below $28\;{\mu}m$. However, we started to figure the mirror for the target value of RMS $\lambda$/20, because system surface figure error would be increased by the error induced by the optical axis adjustment, mirror cell installation, and others. The radius of curvature of the primary mirror was 1,946 mm after the correction. Its measured surface figure error was less than RMS $\lambda$/20 on the table of polishing machine, and RMS $\lambda$/15 after installation in the primary mirror cell. A test observation performed at Daeduk Observatory at Korea Astronomy and Space Science Institute by utilizing the exiting mount, and resulted in $39.8\;{\mu}m$ of stellar FWHM. It was larger than the value from numerical simulation, and showed wing-shaped stellar image. It turned out that the measured-curvature of the secondary mirror, 1,820 mm, was not the same as the designed one, 1,795.977 mm. We fabricated the secondary mirror to the designed value, and finally obtained a stellar FWHM of $27\;{\mu}m$ after re-installation of the optical system into SSO NESS Observatory in Australia.

• 천문학논총
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• 제32권1호
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• pp.355-357
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• 2017

For future space IR missions, such as SPICA, it is crucial to establish an experimental method for evaluating the performance of mid-IR detectors. In particular, the wavelength dependence of the sensitivity is important but difficult to be measured properly. We are now preparing a testing system for mid-IR Si:As/Si:Sb detectors on SPICA. We have designed a cryogenic optical system in which IR signal light from a pinhole is collimated, passed through an optical filter, and focused onto a detector. With this system, we can measure the photoresponse of the detector for various IR light using optical filters with different wavelength properties. We have fabricated aluminum mirrors which are adopted to minimize thermal distortion effects and evaluated the surface figure errors. The total wavefront error of the optical system is $1.3{\mu}m$ RMS, which is small enough for the target wavelengths ($20-37{\mu}m$) of SPICA. The point spread function measured at a room temperature is consistent with that predicted by the simulation. We report the optical performance of the system at cryogenic temperatures.

• 비파괴검사학회지
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• 제33권3호
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• pp.264-269
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• 2013

Since MFC(macro-fiber composite) transducer has been developed, many researchers have tried to apply this transducer on SHM(structural health monitoring), because it is so flexible and durable that it can be easily embedded to various kinds of structures. The objective of this paper is to figure out the benefits and feasibility of applying MFC transducers to guided wave technique. For this, we have experimentally tested the performance of MFC patches as transmitter and sensors for excitation and reception of guided waves on the thin aluminum alloy plate. In order to enhance the signal accuracy, we applied the FIR filter for noise reduction as well as used STFT(short-time Fourier transform) algorithm to image the guided wave characteristics clearly. From the results, the guided wave generated based on MFC showed good agreement with its theoretical dispersion curves. Moreover, the ultrasonic Lamb wave techniques based on MFC patches in pitch-catch manner was tested for detection of surface notch defects of which depths are 10%, 20%, 30% and 40% of the aluminum plate thickness. Results showed that the notch was detectable well when the notch depth was 10% of the thickness or greater.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.493-493
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• 2014

The manufacturing cost of thin-film photovoltics can potentially be lowered by minimizing the amount of a semiconductor material used to fabricate devices. Thin-film solar cells are typically only a few micrometers thick, whereas crystalline silicon (c-Si) wafer solar cells are $180{\sim}300\mu}m$ thick. As such, thin-film layers do not fully absorb incident light and their energy conversion efficiency is lower compared with that of c-Si wafer solar cells. Therefore, effective light trapping is required to realize commercially viable thin-film cells, particularly for indirect-band-gap semiconductors such as c-Si. An emerging method for light trapping in thin film solar cells is the use of metallic nanostructures that support surface plasmons. Plasmon-enhanced light absorption is shown to increase the cell photocurrent in many types of solar cells, specifically, in c-Si thin-film solar cells and in poly-Si thin film solar cell. By proper engineering of these structures, light can be concentrated and coupled into a thin semiconductor layer to increase light absorption. In many cases, silver (Ag) nanoparticles (NP) are formed either on the front surface or on the rear surface on the cells. In case of poly-Si thin film solar cells, Ag NPs are formed on the rear surface of the cells due to longer wavelengths are not perfectly absorbed in the active layer on the first path. In our cells, shorter wavelengths typically 300~500 nm are also not effectively absorbed. For this reason, a new concept of plasmonic nanostructure which is NPs formed both the front - and the rear - surface is worth testing. In this simulation Al NPs were located onto glass because Al has much lower parasitic absorption than other metal NPs. In case of Ag NP, it features parasitic absorption in the optical frequency range. On the other hand, Al NP, which is non-resonant metal NP, is characterized with a higher density of conduction electrons, resulting in highly negative dielectric permittivity. It makes them more suitable for the forward scattering configuration. In addition to this, Ag NP is located on the rear surface of the cell. Ag NPs showed good performance enhancement when they are located on the rear surface of our cells. In this simulation, Al NPs are located on glass and Ag NP is located on the rear Si surface. The structure for the simulation is shown in figure 1. Figure 2 shows FDTD-simulated absorption graphs of the proposed and reference structures. In the simulation, the front of the cell has Al NPs with 70 nm radius and 12.5% coverage; and the rear of the cell has Ag NPs with 157 nm in radius and 41.5% coverage. Such a structure shows better light absorption in 300~550 nm than that of the reference cell without any NPs and the structure with Ag NP on rear only. Therefore, it can be expected that enhanced light absorption of the structure with Al NP on front at 300~550 nm can contribute to the photocurrent enhancement.

• 분석과학
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• 제27권6호
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• pp.284-291
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• 2014

차량 실내 공기질 대응 프로세스는 두 단계의 시험 방법으로 이루어져 있다. 먼저 모듈 부품평가를 통해 차량 실내 VOCs의 주요 원인을 찾고, 절단 시험편을 이용하여 VOCs가 주로 방출되는 소재를 찾는다. 만약 VOCs가 주로 방출되는 소재를 확인 시, 소재 개선을 통해 차량과 모듈 부품에서 방출되는 VOCs를 줄일 수 있다. 하지만 기존의 절단 시험편을 이용한 시험법은 VOCs 원인을 찾는데는 절단면에서의 방출 문제가 있기 때문에, 구성 부품 단위의 평가방법 적용이 필요하다. ISO 12219-5 시험 방법은 부품 절단없이 평가를 하기 때문에 소재 및 표면적의 영향이 함께 고려되어, 모듈 부품에서 구성 부품의 VOCs 영향도 확인이 가능하였다. 트림과 콘솔의 구성부품 평가를 통해 모듈내의 주요 원인 부품을 확인할 수 있었다. 또한 ISO 12219-5 모듈 부품 시험법과 구성 부품 시험법간의 정량적 상관관계 규명을 통해 품질관리를 위한 관리값을 설정할 수 있었다.