• Journal of the Korean Ceramic Society
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• v.41 no.10 s.269
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• pp.766-770
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• 2004

High-transmittance film was coated by using spherical silica nano colloids. Silica colloid sol was preservred between two inclined slide glasses by capillary force, and particles were stacked to form a film onto the substrate as the upper glass was sliding. As the sliding speed increased, the thickness of the film decreased and light transmittance varied. The microstructure observed by SEM showed that silica particles were nearly close packed, which enabled the calculation of the effective refractive index of the film. The film thickness calculated from the wavelength of maximum transmittance and the effective refractive index was well coincided with the thickness observed by SEM and measured by profiler. The maximum transmittance of $94.7\%$ was obtained. This means that $97.4\%$ of transmittance or $1.3\%$ of reflectance can be achieved by simple process if both sides of the substrate are coated.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.118-118
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• 2013

DMM은 방사광가속기의 백색광으로부터 단색광을 추출하기 위해 두 개의 다층 박막 (multilayer) 거울을 사용하는데, 첫 번째 거울은 Bragg 반사를 통해 분광을 하여 단색광을 생산하는 용도이고, 두 번째 거울은 이 단색광을 반사시켜 지면과 평행하게 출사되게 하기 위함이다. 일반적으로 사용되는 DCM (Double Crystal Monochromator)과의 차이점은, Bragg 반사를 위해 DCM에서는 결정을 사용하는 반면 DMM은 밀도차이가 많이나는 두 종류의 물질을 교대로 쌓아 올린 다층 박막을 사용한다는 것이다. 다층 박막의 주기가 곧 Bragg 반사에서의 d-spacing이 되며, X-선 분광의 목적으로 사용되는 d-spacing은 10-50 $\AA$ 사이이다. DCM이 0.01% 대의 우수한 에너지 분해능을 보이는데 비해, DMM은 1% 정도이다. 이 때문에 출사광의 밝기가 DCM에 비해 100배 밝은 특징이 있어서 에너지 분해능보다 광량이 더 중요한 응용에서 DMM이 사용된다. X-선 영상이나 방사선치료가 바로 이러한 응용에 해당한다. DMM은 포항가속기연구소와 (주) 벡트론에서 공동 설계하였으며, (주)벡트론에서 제작하였다. 그림 1에 DMM의 외형과 내부 구조를 나타내었다. Bragg 각의 조절 범위는 0.24-0.9도 이다. 입사광과 출사광의 수직 방향 offset을 10 mm로 유지하기 위해 두 번째 다층 박막이 수평방향으로 1,000 mm 가량 이동할 수 있어야 한다. 이를 위해 두 대의 고니오미터 stage를 사용하여 각각 첫 번째 및 두 번째 다층 박막의 위치와 방향을 제어한다. 첫 번째 다층 박막을 제어하는 고니오미터 stage는 하부가 전체 프레임에 고정되어 있고, 이 고니오미터의 회전축에서 Bragg 각을 조절한다. 두 번째 다층 박막을 제어하는 고니오미터 stage는 높이방향과 수평방향으로 이동이 가능하다. 다층 박막의 pitch는 고니오미터의 회전축에서 조절한다. 그리고 tilt stage를 사용하여 다층 박막의 roll을 조절한다.

• Journal of the Korean Geotechnical Society
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• v.23 no.1
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• pp.51-65
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• 2007

The purpose of this study is the development and application of a high resolution ultrasonic wave imaging system to detect discontinuity plane in lab-scale rock models. This technique is based on received time series which capture the multiple reflections at interface. This study includes the fundamental aspects of ultrasonic wave propagation in rock mass, the selection of the optimal ultrasonic wave transducer, data gathering, a signal processing, imaging methods, and experiments. Experiments are carried out by the horizontal movement and rotation devices. Experimental studies show the discontinuity is well detected by the horizontal movement and rotation devices under water. Furthermore, the discontinuity and the cavity on the plaster block are identified by the rotation device. This study suggests that the new method may be an economical and effective tool for the detection of the discontinuity on rock mass.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.6-11
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• 2004

The playback wavelength shift and the optical property stabilization of the reflection type photopolymer OmniDex film are studied as a function of pressure. As the center wavelength is changed from 632 nm to 482 nm, the bandwidth is 27％ broadened and the diffraction efficiency deviation maintained lower than 10％. These results show that the proposed color tuning method minimizes the change of optical properties more than 50％ compared with the diffusion-based method as the center wavelength changed from 511 nm to 630 nm. The press-based color tuning method shows that it could be used to make holographic optical elements that operate at wavelengths where lasers are not readily available for reflection type holographic recording.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.5
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• pp.757-765
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• 1999

In this paper, L-Type aperture coupled circular polarization patch antenna for mobile communication(IMT-2000, 1.9375 GHz), which is capable of being mounted in mobile unit, was designed and fabricated. This antenna is expanded to the $2\times2$ circular polarization array antenna for satellite mobile communications which are using the L-band frequency. The results are as followings : Returnloss 18.56 dB, beamwidth $60^{\circ}$, gain 7 dBd, axial ratio 0.9 dB in the case of single element and returnloss 28.43 dB, beamwidth $38^{\circ}$, gain 9.8dBd, axial ratio 1.5 dB in the case of $2\times2$ array, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.8
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• pp.967-975
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• 2012

This paper presents a method to measure reflection coefficients of microwave devices or antennas based on time domain analysis with sampling oscilloscopes. The reflection coefficients were extracted by the Fourier transformation of echo pulses from devices with respect to the 20 GHz incident pulse signals. The three-error terms, which are commonly used for the correction of a microwave network, were determined using a 3.5 mm calibration kit. In addition, a modified error-correction model associated with a directional coupler for reflection coefficient measurements is introduced. The results were compared with those of measured with a commercial vector network analyzer.

• The Journal of Korean society of community based occupational therapy
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• v.8 no.3
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• pp.91-106
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• 2018

The purpose of this paper is to review vestibulo-ocular reflex and vestibular rehabilitation for balace problem in elderly. Falling is a common problem associated with aging. Falling and the resulting consequences constitutes one of the most common and serious problems. Balance deficits are one of the top risk factors for falling. Three systems(visual, vestibular and somatosensory) need to be integrated and used to coordinate and control balance. During normal ambulation and head movement, the vestibulo-ocular reflex(VOR) stabilizes gaze, and helps to keep the image of the retina. There is a direct association between deficits in VOR and falls. Older adults have a decreased ability to enhance and suppress the VOR. Vestibular rehabilitation(VR) is an exercise-based group of approaches that began with the aim of central nervous system compensation. VR restores VOR gain and reduces error using repetitive movements of the head and eyes. Many researches showd balance and gait tests were superior in the VR group. It is considered this article helps to prevent elderly falling with vestibular rehabilitation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.449-449
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• 2009

텍스쳐링에 의한 실리콘 태양전지의 표면 반사율 감소는 태양전지의 효율에 있어서 개선해야 할 문제 중 하나이다. 결정질 실리콘 태양전지의 경우 텍스쳐링에 사용되는 용액에 따라 표면 피라미드 분포 형태와 크기의 차이가 나고 그에 따라 각각 다른 반사율을 얻을 수 있다. 이 논문에서는 결정질 실리콘 태양전지에 산 알칼리 용액에 의한 표면 텍스쳐링을 이용하여 균일한 표면 피라미드 형성과 반사율을 감소시킬 수 있는 방안에 대하여 연구하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.510-514
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• 2006

역경계요소법에 기초한 근접음장 음향홀로그래피는 근접 음장에서의 음압 측정과 음향경계요소법을 이용한 전달함수를 이용하여 소음원의 특성을 재구성하고, 임의 형상의을 갖는 소음원을 재구성 할 수 있는 강점이 있지만, 음압 측정에 많은 마이크로폰이 필요로 한다. 많은 실험 비용을 줄이기 위해, 본 연구에서는 마이크로폰이 고정된 상태에서 반사체를 추가하여 음장을 변화시키고, 이 상태에서 측정된 음압을 음원 재구성의 추가 정보로 이용하는 방법이 제안되고, 적용예제로서 모터의 표면 속도를 재구성 하였다. 직육면체 강체 반사체를 이용하여, 각 마이크로폰 위치에서 2 배수의 음압을 얻어, 이를 재구성에 이용하였다. 또한 수치유효랭크를 이용하여 재구성에 사용된 모우드의 개수를 계산하였다.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.331-336
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• 2004

The phase change due to the reflection from target surfaces in a white-light interferometer induces measurement errors when target surfaces are composed of dissimilar materials. We prove that this phase change on reflection as the polarization of the white-light changes causes a shift of both envelope peak position and fringe peak position of several tens of nanometers as the polarization of the white-light changes. In addition, we propose a new equation for white-light interference fringes depending on the polarization of the source.