• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.978-981
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• 2005

The vibration analysis of damped sandwich beam is conducted using finite element method. The equation of motion presented by Mead and Markus is used to formulate FEM. Also as the thickness of the core in the damped sandwich beam goes to zero, conventional beam theory based on the transformed-section method and the equation of Mead and Markus are compared. According to the change of thickness and loss factor of the core, the forced frequency response of beam is calculated and discussed. And then using the half-power band width method, the damping ratio of each mode is calculated and discussed about each case.

• 한국전자파학회논문지
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• 제18권8호
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• pp.943-953
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• 2007

본 논문에서는 Ka-band에서 동작하는 스칼라 급전 혼을 가진 카셋그레인 안테나를 개발하였다. 카셋그레인 안테나의 효과적인 EM 시뮬레이션을 위해 계산된 급전 혼의 근거리장을 표면 등가 이론을 이용하여 카셋그레인의 등가 전원으로 사용하였다. 급전 혼은 $HE_{11}$ 모드로 동작하는 주름 원형 혼 안테나를 사용하였으며, 카셋그레인의 주 부경 각도 및 급전 중심점을 안테나 효율이 최대가 되도록 설계하였다. 제안된 급전 혼 안테나는 33 GHz에서 19 dBi 이득을 보이며, 부엽의 크기는 -25dB 이하, $20^{\circ}$의 반전력 빔 폭을 가졌다. 카셋그레인 안테나는 33GHz에서 41 dBi 이득을 가져 60%의 안테나 효율을 보이며 부엽기 크기는 -20dB 이하, $1.2^{\circ}$의 반전력 빔 폭을 보였다.

• 한국군사과학기술학회지
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• 제16권6호
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• pp.833-840
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• 2013

A radar altimeter which measures the distance using radio wave developed by domestic technology has been applied to various missiles. It is used also for calculating the error of integrated navigation technique. There are a couple of methods to reduce the error but in this paper, we proposed to utilize existing C-band radar altimeter main body with frequency conversion. We designed and manufactured the frequency converter and Ku-band antenna to accomplish this goal. From the test results of products' function and performance, we could expect the possibility of applying this method to enhance the missiles' integrated performance.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.93-100
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• 2008

Recently, due to the advanced measurement techniques, long-term health monitoring systems have been frequently applied to existing bridges. It is known that damping ratios as one of dynamic properties would be an important parameter for evaluating the bridge condition. However, damping ratios may be normally varied depending on the external loading effects on bridges. In general, both the logarithmic decrement and the half-power band width method as a conventional method can be simply used for evaluating the damping ratios accurately when bridge response signals are measured under free vibration conditions. In this study, the Hilbert-Huang transform and the extended Kalman filter were applied to evaluate the damping ratio by using the bridge acceleration signals measured under ambient vibration condition. From the results under ambient vibration condition of bridges, it was examined that the damping ratios evaluated from both the Hilbert-Huang transform and the extended Kalman filter could be more reliable than those from conventional methods.

• 한국소음진동공학회논문집
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• 제19권3호
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• pp.294-300
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• 2009

In high speed railway bridges, dynamic analysis is important because of high passing velocity and moving load at the regular intervals, and damping ratio is a major parameter to predict dynamic responses. In this paper, damping ratios were estimated by using half power band width method and extended Kalman filter according to acceleration signal conditions, and a relationship between estimated damping ratios and representative values of bridge vibration was derived. From the results, damping ratios estimated from total ambient vibration were more reliable than only free vibration part. In case of using extended Kalman filter, the estimated damping ratios varying with RMQ(root mean quad), as one of representative values of bridge vibration, have more feasible trend. Thus, it is shown that further studies on reliabilities of estimated damping ratios are needed.

• 대한전자공학회논문지TC
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• 제39권5호
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• pp.251-258
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• 2002

본 논문에서는 기존외 야기-우다 안테나 배열이론을 마이크로스트립 안테나에 접목시킨 X밴드용 다이폴 급전 평면배열 안테나를 설계하고 제작하였다. 그리고 넓은 대역폭을 갖는 무선통신 시스팀에 쉽게 적용시킬수 있는 다이폴 급전 평면배열 안테나의 설계 절차에 대하여 기술하였다. 또한 FDTD 수치해석법을 이용하여 안테나의 복사특성, 반사손실과 대역폭을 개선시켰으며 제작을 통해 평면형 안테나 해석의 타당성을 입증하였다. 제작한 결과, 10GHz의 중심주파수에서 안테나의 이득은 4.9dBi이고 대역폭은 약 40%, 전후방비는 16dB, E면과 H면의 반 전력 빔폭은 각각 117°와 156°이다. VSWR<2를 기준으로 했을 때, 7.4GHz∼11.88GHZ의 주파수 범위에서 측정결과와 이론적인 결과가 비교적 잘 일치하였다.

• Transactions on Electrical and Electronic Materials
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• 제12권2호
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• pp.51-55
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• 2011

We investigated the etching characteristics of zinc oxide (ZnO) thin films deposited by the atomic layer deposition method. The gases of the inductively coupled plasma chemistry consisted of $Cl_2$, Ar, and $O_2$. The maximum etch rate was 40.3 nm/min at a gas flow ratio of $Cl_2$/Ar=15:5 sccm, radio-frequency power of 600 W, bias power of 200 W, and process pressure of 2 Pa. We also investigated the plasma induced damage in the etched ZnO thin films using X-ray diffraction (XRD), atomic force microscopy and photoluminescence (PL). A highly oriented (100) peak was present in the XRD spectroscopy of the ZnO samples. The full width at half maximum value of the ZnO sample etched using the $O_2/Cl_2$/Ar chemistry was higher than that of the as-deposited sample. The roughness of the ZnO thin films increased from 1.91 nm to 2.45 nm after etching in the $O_2/Cl_2$/Ar plasma chemistry. Also, we obtained a strong band edge emission at 380 nm. The intensities of the peaks in the PL spectra from the samples etched in all of the chemistries were increased. However, there was no deep level emission.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.