• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.470-478
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• 2015

A heuristic method treating a layered ocean bottom in a ray modeling is to use the plane wave reflection coefficient for multiple-layered structure, named an one-layer assumption in this paper. We examine the validity of one-layer assumption in the case of two-layered ocean bottom, and obtain a simple inequality condition depending on the sound speed ratio, the ratio of layer thickness to source-receiver range, and the grazing angle of first reflected ray. From this inequality condition, it is shown that an one-layer assumption can be applicable to ray propagation problems at mid frequencies. Finally, numerical experiments are performed in the ocean environment similar to the East Sea in Korea. Incoherent transmission loss is calculated by the geometrical beam model with the plane wave reflection coefficient for multiple-layered ocean bottom and compared with the result of SNUPE 2.0, which is a parabolic equation package developed in Seoul National University.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.287-287
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• 2011

ITRS(international technology roadmap for semiconductors)에 따르면 MOS (metal-oxide-semiconductor)의 CD(critical dimension)가 45 nm node이하로 줄어들면서 poly-Si/SiO2를 대체할 수 있는 poly-Si/metal gate/high-k dielectric이 대두되고 있다. 일반적으로 metal gate를 식각시 정확한 CD를 형성시키기 위해서 plasma를 이용한 RIE(reactive ion etching)를 사용하고 있지만 PIDs(plasma induced damages)의 하나인 PICD(plasma induced charging damage)의 발생이 문제가 되고 있다. PICD의 원인으로 plasma의 non-uniform으로 locally imbalanced한 ion과 electron이 PICC(plasma induced charging current)를 gate oxide에 발생시켜 gate oxide의 interface에 trap을 형성시키므로 그 결과 소자 특성 저하가 보고되고 있다. 그러므로 본 연구에서는 이에 차세대 MOS의 metal gate의 식각공정에 HDP(high density plasma)의 ICP(inductively coupled plasma) source를 이용한 중성빔 시스템을 사용하여 PICD를 줄일 수 있는 새로운 식각 공정에 대한 연구를 하였다. 식각공정조건으로 gas는 HBr 12 sccm (80%)와 Cl2 3 sccm (20%)와 power는 300 w를 사용하였고 200 eV의 에너지로 식각공정시 TEM(transmission electron microscopy)으로 TiN의 anisotropic한 형상을 볼 수 있었고 100 eV 이하의 에너지로 식각공정시 하부층인 HfO2와 높은 etch selectivity로 etch stop을 시킬 수 있었다. 실제 공정을 MOS의 metal gate에 적용시켜 metal gate/high-k dielectric CMOSFETs의 NCSU(North Carolina State University) CVC model로 effective electric field electron mobility를 구한 결과 electorn mobility의 증가를 볼 수 있었고 또한 mos parameter인 transconductance (Gm)의 증가를 볼 수 있었다. 그 원인으로 CP(Charge pumping) 1MHz로 gate oxide의 inteface의 분석 결과 이러한 결과가 gate oxide의 interface trap양의 감소로 개선으로 기인함을 확인할 수 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.134-138
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• 2021

Various types of precision plastic thin films are used widely in high-performance displays, such as smartphones. For plastic thin-films manufactured by the Roll-to-Roll process, the film thickness must be measured and managed while moving. In the Roll-to-Roll process, wrinkles are generated when tension is applied to the film, which causes an inclination on the optical axis of the thickness gauge, resulting in a loss of accuracy. Therefore, this study attempted to develop an optical interference tomography measurement system. In this study, the tilt angle of the film was measured to correct the measurement value error in the thickness gauge caused by the tilt of the film. The system was constructed so that the laser was irradiated on the tilted film, and the laser reflected from the film was formed on the PSD. The relationship between the tilt angle of the film and the output value of the PSD was obtained experimentally. Using this, a device to measure the tilt angle of the film was constructed, and angle measurements were taken at a speed of 250,000Hz.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.2
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• pp.34-40
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• 1993

A microstrip antenna for mobile system are designed at the resont frequency 0.88 GHz. The microstrip array antenna are designed to depend on the size of rectanular microstrip path for the relative current distribution to be 1:4.69:1 using Tchebyscheff polynominals. Gain difference between the main lobe and sidelobe is calculated for theoritical values of 20 dB. The designed microstrip array antenna are mesureed various characteristics, such as return loss, radiation pattern, V.S.W.R, bandwidth, and agreed with each other and theoretical value. Also it is presented a process of phase variation of patch array antenna depend on relative current distribution for beam scanning.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1025-1033
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• 2012

Fabry-Perot cavity(FPC) antennas with artificial magnetic conductor(AMC) surface are designed in order to provide scan capability by $4{\times}1$ array feed inside the cavity. The proposed antenna, excited by $4{\times}1$ thinned array, not only achieve higher directivities but also improve suppression of sidelobe level(SLL) relative to that of the thin array alone. The FPC antenna with the height of a quarter wavelength generate maximum gain of 19 dB, SLL suppression of 14 dB and maximum scan angle of $8^{\circ}$ under the feed phase difference of $90^{\circ}$ at the design frequency of 12 GHz.

• 한국HCI학회:학술대회논문집
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• 2007.02b
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• pp.219-225
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• 2007

컴퓨터교과는 학생들의 일반적인 학업성취 개인차 요인과 더불어 필수 교과가 아니기 때문에 학교 혹은 교사마다 교육하는 내용이 상이하여 학생들이 상급학교로 진학하였을 때 학생들 간의 수준 차가 심화된다. 이러한 다양한 수준차가 있는 학생들을 교사 1인이 한정된 시간 안에 모든 학생들의 수준에 맞추어 지도하는 것은 대단히 어렵다. 또 넓은 컴퓨터실에서는 학생들의 주위가 분산될 우려가 많으므로 학생들의 행동을 수시로 관리할 필요가 있다. 이러한 컴퓨터교과 실습수업 시에는 보다 효과적인 지도방법이 요구된다. 이에 본 연구에서는 컴퓨터교과 실습지도 방법의 장단점을 분석하고, 컴퓨터교과 실습수업 시 널리 사용되는 시범 실습법의 단점을 보완할 수 있는 도우미학생 활용 시범 실습법을 제안하고, 중학교 컴퓨터 정규교과 시간에 적용하여 그 효과를 검증하였다. 도우미학생 활용 시범 실습법이란 교사는 실습내용을 설명하고, 모든 학생들은 교사의 설명과 동시에 실습을 하며, 도우미학생의 실습내용이 빔 프로젝트를 통해 다른 학생들에게 보여짐으로써 교사의 시범을 대신하는 방법을 말한다. 컴퓨터교과는 설명만으로도 실습 가능한 내용이 많아 이러한 지도방법이 가능하다 이 방법은 실습내용을 최소한의 작은 단계로 구분하고, 각 단계별로 교사의 설명과 개별지도, 모든 학생의 실습과 관찰이 동시에 이루어진다. 이 방법은 교사의 행동이 자유로워 설명과 동시에 개별지도가 가능해 개별지도의 확대를 가져올 수 있으며, 학생들에게 보다 많은 즉각적인 피드백을 줄 수 있으며, 학생들의 행동을 수시로 관리할 수 있다는 장점이 있다. 또한 본 연구에서는 검증도구로 'html 태그' 단원 5차시 분량의 과제수행능력평가도구를 개발하여 사용하였다. 검증결과 학업성취 중하수준의 도우미학생 활용 시범 실습으로 수업한 집단은 통제반과 유의미한 차이가 없었으나, 학업성취 중상수준의 도우미학생 활용 시범실습으로 수업한 집단은 통제반에 비해 과제수행능력에 있어서 유의미한 차이를 보였다 이로써 제안한 지도방법의 효과성을 입증하였다.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.8
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• pp.1-11
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• 1998

One of the desired features for the realizations of high quality Information and Telecommunication services in future is "the Sensation of Reality". This will be achieved only with the visual communication based on the 3- dimensional (3-D) moving images. The main difficulties in realizing 3-D moving image communication are that there is no developed data transmission technology for the hugh amount of data involved in 3-D images and no established technologies for 3-D image recording and displaying in real time. The currently known stereoscopic imaging technologies can only present depth, no moving parallax, so they are not effective in creating the sensation of the reality without taking eye glasses. The more effective 3-D imaging technologies for achieving the sensation of reality are those based on the multiview 3-D images which provides the object image changes as the eyes move to different directions. In this paper, a multiview 3-D imaging system composed of 8 CCD cameras in a case, a RGB(Red, Green, Blue) beam projector, and a holographic screen is introduced. In this system, the 8 view images are recorded by the 8 CCD cameras and the images are transmitted to the beam projector in sequence by a signal converter. This signal converter converts each camera signal into 3 different color signals, i.e., RGB signals, combines each color signal from the 8 cameras into a serial signal train by multiplexing and drives the corresponding color channel of the beam projector to 480Hz frame rate. The beam projector projects images to the holographic screen through a LCD shutter. The LCD shutter consists of 8 LCD strips. The image of each LCD strip, created by the holographic screen, forms as sub-viewing zone. Since the ON period and sequence of the LCD strips are synchronized with those of the camera image sampling adn the beam projector image projection, the multiview 3-D moving images are viewed at the viewing zone.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.1
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• pp.18-24
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• 2006

Reactor core and internal structures of a liquid metal reactor (LMR) can not be visually examined due to an opaque liquid sodium. The under-sodium viewing technique by using an ultrasonic wave should be applied far the visual inspection of reactor internals. In this study, an ultrasonic waveguide sensor with a strip plate has been developed for an application to the under-sodium viewing technique. The Lamb wave propagation of a waveguide sensor has been analyzed and the zero-order antisymmetric $A_0$ plate wave was selected as the application mode of the sensor. The $A_0$ plate wave can be propagated in the dispersive low frequency range by using a liquid wedge clamped to the waveguide. A new technique is presented which is capable of steering the radiation beam angle of a waveguide sensor without a mechanical movement of the sensor assembly The steering function of the ultrasonic radiation beam can be achieved by a frequency tuning method of the excitation pulse in the dispersive range of the $A_0$ mode. The technique provides an opportunity to overcome the scanning limitation of a waveguide sensor. The beam steering function has been evaluated by an experimental verification. The ultrasonic C-scanning experiments are performed in water and the feasibility of the ultrasonic waveguide sensor has been verified.

• Progress in Medical Physics
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• v.23 no.3
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• pp.188-198
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• 2012

This study aims to evaluate the accuracy of the collapsed cone convolution (CCC) algorithm for dose calculation in a treatment planning system (TPS), CorePLAN$^{TM}$. We implemented beam models for various setup conditions in TPS and calculated radiation dose using CCC algorithm for 6 MV and 15 MV photon beam in $50{\times}50{\times}50cm^3$ water phantom. Field sizes were $4{\times}4cm^2$, $6{\times}6cm^2$, $10{\times}10cm^2$, $20{\times}20cm^2$, $30{\times}30cm^2$ and $40{\times}40cm^2$ and each case was classified as open beam cases and wedged beam cases, respectively. Generated beam models were evaluated by comparing calculated data and measured data of percent depth dose (PDD) and lateral profile. As a result, PDD showed good agreement within approximately 2% in open beam cases and 3% in wedged beam cases except for build-up region and lateral profile also correspond within approximately 1% in field and 4% in penumbra region. On the other hand, the discrepancies were found approximately 4% in wedged beam cases. This study has demonstrated the accuracy of beam model-based CCC algorithm in CorePLAN$^{TM}$ and the most of results from this study were acceptable according to international standards. Although, the area with large dose difference shown in this study was not significant region in clinical field, the result of our study would open the possibility to apply CorePLAN$^{TM}$ into clinical field.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.287.1-287.1
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• 2014

본 연구에서는 현재 디스플레이에서 가장 널리 이용되는 저온 polycrystalline silicon (poly-Si)의 결정화 방법에 따른 thin-film transistor (TFT)의 전기적 특성을 분석하였다. 분석에 이용된 결정화 방식은 Excimer Laser Annealing (ELA)와 Metal Induced Crystallization (MIC)이다. ELA와 MIC TFTs의 전기적 특성 측정을 통한 분석결과 ELA와 MIC poly-Si TFTs의 전기적 특성 [field-effect mobility (${\mu}_{FE}$), on/off current ratio ($I_{ON}/I_{OFF}$), sub-threshold swing (SS)]은 큰 차이는 없지만, ELA를 이용한 poly-Si TFT의 전기적 특성이 조금 우수하다. 하지만, MIC poly-Si TFT의 경우 threshold voltage ($V_{TH}$)가 0V에 보다 가까울 뿐만 아니라, 전기적 스트레스를 통한 신뢰성 확인 시 ELA poly-Si TFT보다 조금 더 안정적이다. 이는 ELA의 경우 좁은 면에 선형 레이저 빔으로 조사하면서 생기는 hill-lock의 영향으로 표면이 거칠고 균일하지 못하여 바이어스 인가시 생기는 문제이다. 또한 MIC는 금속 촉매를 이용해 결정립 경계를 확장하고 결정 크기를 키워 대면적화에 유리하다. Thermal Stress에서는 (from 293K to 373K) TFT에 점차 높은 온도를 가하자 MIC poly-Si TFT의 경우 off 상태에서 누설 전류 값이 증가하며 열에 민감한 반응을 보이는 것을 확인하였다.