• 한국전자파학회논문지
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• 제26권6호
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• pp.525-532
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• 2015

본 논문에서는 대형 구조체에 장착된 안테나의 효율적인 성능예측을 위하여, 열린 도파관을 이용한 배열안테나 해석등가 모델링 기법을 제안하였다. 등가 모델을 구현하기 위하여 우선 배열 안테나의 개별 소자를 열린 도파관 형상으로 설계하였으며, 도파관의 깊이, 도파관의 개구면 넓이, 그라운드의 크기를 조절하여 원하는 개별 소자의 방사패턴의 도출이 가능하도록 하였다. 개발된 개별 소자를 두 가지 타입의 배열안테나의 등가 모델링에 적용하였다. 등가모델을 이용하여 도출된 안테나의 성능을 원본 안테나의 해석 성능과 비교하였으며, 최대이득은 0.2 dB, 반전력 빔폭은 $1^{\circ}$ 이내의 오차를 보여, 등가모델을 이용한 원본 안테나의 성능 모사가 가능함을 확인하였다. 또한, 제안된 등가모델을 간단한 항공기 형상에 장착하여 전자파 해석을 수행하였으며, 원본 안테나를 탑재한 해석 결과와 비교하였고, 그 결과 시뮬레이션 필요 해석 자원 및 해석 시간이 60 % 이상 감소하는 것을 확인하였다.

• 한국광학회지
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• 제10권2호
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• pp.107-113
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• 1999

수차가 적은 홀로그래픽 스캐너는 기존의 렌즈나 거울과 같은 광학 소자의 사용 매수를 줄임으로써 제작 가격을 낮출 수 있다는 잠재적인 장점을 갖고 있다. 본 연구에서는 홀로그래픽 스캐너 설계에 광선 추적버블 적용하여 스캔 기능과 초점을 맺는 기능을 동시에 할 수 있는 홀로그래픽 광학 소자를 설계하였으며, 수차가 없는 직선의 스캔 라인을 얻기 위한 기록 및 재생 구조와 hologon 구조에 대해 조사하였다. Prototype으로 제작된 홀로그래픽 스캐너에서 bow는 전체 스캔 폭 300 mm에서 $\pm$133$\mu\textrm{m}$이었으며, spot의 크기는 100 $\mu\textrm{m}$ 이하로 얻을 수 있었다. 실험 결과 광선 추적을 이용한 설계 데이터의 유용성을 검증하였고 레이저 프린터나 디스플레이 분야 등으로의 응용 가능성을 제시하였다.

• 대한조선학회논문집
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• 제44권3호
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• pp.267-278
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• 2007

This experimental study investigated on the eddy making effect on the roll motion of a rectangular barge in a two-dimensional wave tank. The structure was used to simulate a simplified rectangular barge in the beam sea condition. The structure with a draft one half of its height was hinged at the center of gravity and free to roll by waves. The rectangular barge was tested with regular waves with a range of wave periods that are shorter, equal to, and longer than its roll natural period. Particle image velocimetry (PIV) was employed to obtain the velocity field in the vicinity of the structure. The coupled interactions between the incident wave and the barge were demonstrated by examining the vortical flow fields to elucidate the eddy making effect during the roll motion. For incoming wave with a wave period same as the roll natural period, the barge roll motion was reduced by the eddy making damping effect. At the wave period shorter than the roll natural period, the structure roll motion was slightly reduced by the vertical flow around the barge. However, at the wave period longer than the roll natural period, the eddy making effect due to flow separation at structure corners indeed amplifies the roll motion. This indicates that not only can the eddy making effect damp out the roll motion, it can also increase the roll motion.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.187-187
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• 2013

양자점(Quuantum dot, QD)은 0차원 특성을 가지는 구조로 양자 구속 효과로 인하여 bulk와 는 다른 구조적, 광학적, 전기적 특성을 가지고 있다. InAs QD는 size와 barrier의 bandgap 조절을 이용하여 쉽게 bandgap을 바꿀 수 있는 장점이 있어 solar cell, semiconductor laser diode, infrared photodetector 등으로 많은 연구가 이루어지고 있다. 일반적으로 Stranski-Krastanov (SK) mode로 성장한 InAs QD는 보통 GaAs epilayer와의 lattice mismatch (7%)를 이용하여 성장을 하고 이로 인하여 strain을 가지고 있고 QD의 density와 stack이 높을수록 strain이 커진다. 하지만 sub-monolayer (SML) QD 같은 경우 wetting layer가 생기는 지점인 1.7 ML이하에서 성장되는 성장 방식으로 SK-QD보다는 작은 strain을 가지게 된다. 또 QD의 size가 작아 SK-QD보다 큰 bandgap을 가지고 있다. 본 연구에서는 분자선 에피택시(molecular beam epitaxy, MBE)를 이용하여 semi-insulating GaAs substrate 위에 InAs QD를 0.5/1/1.5/1.7/2/2.5 monolayer로 성장을 하였다. GaAs과 InAs의 성장온도와 성장속도는 각각 $590^{\circ}C$, 0.8 ML/s와 $480^{\circ}C$, 0.2 ML/s로 성장을 하였으며 적층사이의 interruption 시간은 10초로 고정하였고 10주기를 성장하였다. Photoluminescence (PL)측정 결과 SML-QD는 size에 따라서 energy가 1.328에서 1.314 eV로 약간 red shift를 하였고 SK-QD의 경우 1.2 eV의 energy정도로 0.1 eV이상 red shift 하였다. 이는 QD size에 의하여 energy shift가 있다고 사료된다. 또 wetting layer의 경우 1.41 eV의 energy를 가지는 것으로 확인 하였다. SML-QD는 SK-QD 보다 반치폭(full width at half maximum, FWHM)이 작은 것은 확인을 하였고 strain field의 감소로 해석된다. 하지만 SML-QD의 경우 SK-QD보다 상대적으로 작은 PL intensity를 가지고 있었다. 이를 개선하기 위해서는 보다 높은 QD density를 요구하게 되는데 growth temperature, V/III ratio, growth rate 등을 변화주어서 연구할 계획이다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제4권2호
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• pp.117-123
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• 2004

A 30 nm $In_{0.7}GaAs$ High Electron Mobility Transistor (HEMT) with triple-gate has been successfully fabricated using the $SiO_2/SiN_x$ sidewall process and BCB planarization. The sidewall gate process was used to obtain finer lines, and the width of the initial line could be lessened to half by this process. To fill the Schottky metal effectively to a narrow gate line after applying the developed sidewall process, the sputtered tungsten (W) metal was utilized instead of conventional e-beam evaporated metal. To reduce the parasitic capacitance through dielectric layers and the gate metal resistance ($R_g$), the etchedback BCB with a low dielectric constant was used as the supporting layer of a wide gate head, which also offered extremely low Rg of 1.7 Ohm for a total gate width ($W_g$) of 2x100m. The fabricated 30nm $In_{0.7}GaAs$ HEMTs showed $V_{th}$of -0.4V, $G_{m,max}$ of 1.7S/mm, and $f_T$ of 421GHz. These results indicate that InGaAs nano-HEMT with excellent device performance could be successfully fabricated through a reproducible and damage-free sidewall process without the aid of state-of-the-art lithography equipment. We also believe that the developed process will be directly applicable to the fabrication of deep sub-50nm InGaAs HEMTs if the initial line length can be reduced to below 50nm order.

• 한국전자파학회논문지
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• 제19권10호
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• pp.1166-1174
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• 2008

본 논문에서는 $2{\sim}18$ GHz 광대역 캐비티 백 스파이럴 안테나 설계에 대하여 기술하였다. Archimedean 스파이럴 안테나의 설계 기법을 바탕으로 스파이럴 안테나의 암 패턴과 백 캐비티를 설계하고, CST사의 MWS를 이용하여 시뮬레이션 하였다. 시뮬레이션을 통하여 안테나의 VSWR, 축비(axial ratio) 그리고 반전력 빔 폭을 고찰하였다. 또한, 동작 대역에서 요구되는 VSWR 특성을 만족시키는 Marchand 동축형 밸런을 설계하였다. 최종적으로 제작 및 측정을 통해 안테나의 성능 및 설계 방법의 타당성을 검증하였다.

• Structural Monitoring and Maintenance
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• 제6권4호
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• pp.317-346
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• 2019

Performance assessment of pavements proves useful, in terms of handling the ride quality, controlling the travel time of vehicles and adequate maintenance of pavements. Roughness profiles provide a good measure of the deteriorating condition of the pavement. For the accurate estimates of pavement roughness from dynamic vehicle responses, vehicle parameters should be known accurately. Information on vehicle parameters is uncertain, due to the wear and tear over time. Hence, condition monitoring of pavement requires the identification of pavement roughness along with vehicle parameters. The present study proposes a scheme which estimates the roughness profile of the pavement with the use of accurate estimates of vehicle parameters computed in parallel. Pavement model used in this study is a two-layer Euler-Bernoulli beam resting on a nonlinear Pasternak foundation. The asphalt topping of the pavement in the top layer is modeled as viscoelastic, and the base course bottom layer is modeled as elastic. The viscoelastic response of the top layer is modeled with the help of the Burgers model. The vehicle model considered in this study is a half car model, fitted with accelerometers at specified points. The identification of the coupled system of vehicle-pavement interaction employs a coupled scheme of an unbiased minimum variance estimator and an optimization scheme. The partitioning of observed noisy quantities to be used in the two schemes is investigated in detail before the analysis. The unbiased minimum variance estimator (MVE) make use of a linear state-space formulation including roughness, to overcome the linearization difficulties as in conventional nonlinear filters. MVE gives estimates for the unknown input and fed into the optimization scheme to yield estimates of vehicle parameters. The issue of ill-posedness of the problem is dealt with by introducing a regularization equivalent term in the objective function, specifically where a large number of parameters are to be estimated. Effect of different objective functions is also studied. The outcome of this research is an overall measure of pavement condition.

• Journal of electromagnetic engineering and science
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• 제18권2호
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• pp.117-128
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• 2018

In this paper, compact linear dual polarized series-fed $1{\times}2$ linear and $2{\times}2$ planar arrays antennas for airborne SAR applications are proposed. The proposed antenna design consists of a square radiating patch that is placed on top of the substrate, a quarter wave transformer and $50-{\Omega}$ matched transformer. Matching between a radiating patch and the $50-{\Omega}$ microstrip line is accomplished through a direct coupled-feed technique with the help of an impedance inverter (${\lambda}/4$ impedance transformer) placed at both horizontal and vertical planes, in the case of the $2{\times}2$ planar array. The overall size for the prototype-1 and prototype-2 fabricated antennas are $1.9305{\times}0.9652{\times}0.05106{{\lambda}_0}^3$ and $1.9305{\times}1.9305{\times}0.05106{{\lambda}_0}^3$, respectively. The fabricated structure has been tested, and the experimental results are similar to the simulated ones. The CST MWS simulated and vector network analyzer measured reflection coefficient ($S_{11}$) results were compared, and they indicate that the proposed antenna prototype-1 yields the impedance bandwidth >140 MHz (9.56-9.72 GHz) defined by $S_{11}$<-10 dB with 1.43%, and $S_{21}$<-25 dB in the case of prototype-2 (9.58-9.74 GHz, $S_{11}$< -10 dB) >140 MHz for all the individual ports. The surface currents and the E- and H-field distributions were studied for a better understanding of the polarization mechanism. The measured results of the proposed dual polarized antenna were in accordance with the simulated analysis and showed good performance of the S-parameters and radiation patterns (co-pol and cross-pol), gain, efficiency, front-to-back ratio, half-power beam width) at the resonant frequency. With these features and its compact size, the proposed antenna will be suitable for X-band airborne synthetic aperture radar applications.

• 대한조선학회지
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• 제6권1호
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• pp.1-24
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• 1969

Chine형선(型船)의 선체진동(船體振動) 또는 운동(運動)의 해석(解析)에 필요(必要)한 부가질량계산(附加質量計算)에 기여(寄與)할 목적(目的)으로 등각사상법(等角寫像法)의 응용(應用), 즉(卽) 실선(實船)과 유사(類似)한 단면형상(斷面形狀)을 주는 2경수근(徑數群) 사상함수(寫像函數)를 얻어 이를 이용(利用)하여 동단면(同斷面)의 주상체(柱狀體)에 대(對)하여 이상유체(理想流體)의 자유수면(自由水面)에서의 상하(上下) 및 수평진동(水平振動)에 대(對)한 부가질량(附加質量)을 계통적(系統的)으로 계산(計算)했으며, 동계산결과(同計算結果)를 상하진동(上下振動)에 대(對)하여서는 Lewis form 주상체(柱狀體) 및 직선요소단면주상체(直線要素斷面柱狀體)에 대(對)한 이론적(理論的) 계산결과(計算結果)와 그리고 수평진동(水平振動)에 대(對)해서는 Lewis form 주상체(柱狀體)에 대(對)한 것과 비교고찰(比較考察)하였다.

• 대한방사선기술학회지:방사선기술과학
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• 제45권2호
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• pp.127-134
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• 2022

In order to overcome the image quality limitations of the conventional C-arm, a flat panel detector (FPD) is used to enhance spatial resolution, detective quantum efficiency, frame rate, and dynamic range. Three-dimensional (3D) visualized information can be obtained from C-arm computed tomography (CT) equipped with an FPD, which can reduce patient discomfort and provide various medical information to health care providers by conducting procedures in the interventional procedure room without moving the patient to the CT scan room. Unlike a conventional C-arm device, a C-arm CT requires different basic safety and essential performance evaluation criteria; therefore, in this study, basic safety and essential performance evaluation criteria to protect patients, medical staff, and radiologists were derived based on International Electrotechnical Commission (IEC) standards, the Ministry of Food and Drug Safety (MFDS) standards in Korea, and the rules on the installation and operation of special medical equipment in Korea. As a result of the study, six basic safety evaluation criteria related to electrical and mechanical radiation safety (leakage current, collision protection, emergency stopping device, overheating, recovery management, and ingress of water or particulate matter into medical electrical (ME) equipment and ME systems: footswitches) and 14 essential performance evaluation criteria (accuracy of tube voltage, accuracy of tube current, accuracy of loading time, accuracy of current time product, reproducibility of radiation output, linearity and consistency in radiography, half layer value in X-ray equipment, focal size and collimator, relationship between X-ray field and image reception area, consistency of light irradiation versus X-ray irradiation, performance of the mechanical device, focal spot to skin distance accuracy, image quality evaluation, and technical characteristic of cone-beam computed tomography) were selected for a total of 20 criteria.