• 대기
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• 제26권3호
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• pp.473-482
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• 2016

An accurate determination of turbulent fluxes over an urban area is a challenging task due to its morphological diversity and associated flow complexity. In this study, an eddy covariance (EC) method is applied over a highly heterogeneous urban area in a small city (Gongju), South Korea to investigate the quantitative influence of 'coordinate tilt' in determining the turbulent fluxes of sensible heat, latent heat, momentum, and carbon dioxide mass. Two widely-used coordinate transform methods are adopted and applied to eight directional sections centered on the site to analyze a 1-year period EC measurement obtained from the urban site: double rotation (DR) and planar fit (PF) transform. The results show that mean streamline planes determined by the PF method are distinguished from the sections, representing morphological heterogeneity of the site. The sectional pitch angles determined by the DR method also compare well with those in the PF method. Both the PF and DR methods show large variabilities in the determined streamline planes at each directional section, implying that flow patterns may form in a complicate way due to the surface heterogeneity. Resulting relative differences of the turbulent fluxes, defined by $(F_{DR}-F_{PF})/F_{DR}$, are found on average +13% in sensible heat flux, +21% in latent heat flux, +37% in momentum flux, and +26% in carbon dioxide mass flux, which are larger values than those reported previously for fairly homogeneous natural sites. The fractional differences depend significantly on wind direction, showing larger differences in northerly winds at the measurement site. It is also found that the relative fractional differences are negatively correlated with the mean wind speed at both stable/unstable atmospheric conditions. These results imply that EC turbulent fluxes determined over heterogeneous urban areas should be carefully interpreted with considering the uncertainty due to 'coordinate tilt' effect in their applications.

• 마이크로전자및패키징학회지
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• 제20권3호
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• pp.19-22
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• 2013

고속, 대용량 정보 전송 수요가 급격하게 증가함에 따라 대량생산 및 고효율의 PLC형 집적 광소자의 연구가 증가하고 있다. 본 논문에서는 광소자와 광섬유가 수동 정렬이 가능하도록 일체형 정렬 구조를 제안하였다. 일체형 구조의 광소자는 기본적으로 1채널의 입력부의 광신호를 2채널의 출력부를 통해 분리하는 광분배기 구조이다. 본 연구에서 제안된 일체형 구조의 제작은 롤투롤 공정 기술을 이용하여 제작하고 그 특성을 평가하였다. 롤투롤 공정 기술은 광소자의 제작에 들어가는 시간을 절감하고 연속생산이 가능한 방법이다. 제작된 광소자의 광특성은 1550 nm의 광원을 이용하여 약3.9 dB의 삽입손실과 0.2 dB의 채널 균일도를 나타내었다.

• 한국전자파학회논문지
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• 제18권9호
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• pp.1015-1022
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• 2007

본 논문에서는 이중층의 패치와 제거된 접지면을 이용하여 광대역 평판형 역 F 안테나(PIFA)를 설계하였다. 제안된 안테나는 급전부를 공유하게 한 이중 층 패치의 슬릿을 통해 공진점을 조절하였고 접지면을 부분 제거하여 임피던스 정합을 개선하였다. 대역폭은 VSWR 2 이하 기준 1,492 MHz(BW: 67.7 %, 1,457${\sim}$2,949 MHz)와 VSWR 2.5 이 하 기준 1,170 MHz(BW: 21 %, 4,970${\sim}$6,140 MHz)를 얻었다. 이는 DCS 1800, DCS1900, UMTS (W-CDMA), WiBro, WLAN(IEEE 802.11b), Satellite DMB, WLAN (IEEE802.11a) 총 7개의 무선 통신 서비스를 만족한다. 방사 패턴은 전 방향에서 신호의 송수신이 가능하였고 대역 내에서 주파수별 서로 유사한 형태를 가졌다.

• 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.

• 한국정밀공학회지
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• 제29권12호
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• pp.1376-1381
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• 2012

Optical devices are used extensively in the field of information network. Increasing demand for optical device, optical interconnection has been a important issue for commercialization. However many problems exist in the interconnection between optical device and optical fiber, and in the case of the multi-channel, problems of the optical alignment and optical array arise. For solving the alignment and array problem of optical device and the optical fiber, we fabricated fiber alignment and array by using imprint technology. Achieved higher precision of optical fiber alignment and array due to fabricating using imprint technology. The silicon stamp with different depth was fabricated using the conventional photolithography. Using the silicon stamp, a nickel stamp was fabricated by electroforming process. We conducted imprint process using the nickel stamp with different depth. The optical alignment and array by fabricating the patterns of optical device and fiber alignment and array using imprint process, and achieved higher precision of decreasing the dimensional error of the patterns by optimization of process. The fabricated optical interconnection of PLC device was measured 3.9 dB and 4.2 dB, lower than criteria specified by international standard.

• 한국자동차공학회논문집
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• 제23권5호
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• pp.463-470
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• 2015

When a camera installed on a vehicle is used, estimation of the camera pose including tilt, roll, and pan angle with respect to the world coordinate system is important to associate camera coordinates with world coordinates. Previous approaches using huge calibration patterns have the disadvantage that the calibration patterns are costly to make and install. And, previous approaches exploiting multiple vanishing points detected in a single image are not suitable for automotive applications as a scene where multiple vanishing points can be captured by a front camera is hard to find in our daily environment. This paper proposes a camera pose estimation method. It collects multiple images of lane markings while changing the horizontal angle with respect to the markings. One vanishing point, the cross point of the left and right lane marking, is detected in each image, and vanishing line is estimated based on the detected vanishing points. Finally, camera pose is estimated from the vanishing line. The proposed method is based on the fact that planar motion does not change the vanishing line of the plane and the normal vector of the plane can be estimated by the vanishing line. Experiments with large and small tilt and roll angle show that the proposed method outputs accurate estimation results respectively. It is verified by checking the lane markings are up right in the bird's eye view image when the pan angle is compensated.

• 한국전기전자재료학회논문지
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• 제29권2호
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• pp.90-94
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• 2016

In this work, [$Pb(Mg_{1/2}W_{1/2})_{0.03}(Ni_{1/3}Nb_{2/3})_x(Zr_{0.5}Ti_{0.5})_{0.97-x}O_3-BiFeO_3$] (x=0.02 to 0.12) composition ceramics were fabricated by the conventional soild state reaction method and their microstructure and piezoelectric properties were investigated according to PNN substitution. The addition of small amount of $BiFeO_3$, $Li_2CO_3$, and $CaCO_3$ were used in order to decrease the sintering temperature of the ceramics. The XRD (x-ray diffraction patterns) of all ceramics exhibited a perovskite structure. The sinterability of PMW-PNN-PZT-BF ceramics was remarkably improved using liquid phase sintering of $CaCO_3$, $Li_2CO_3$. However, it was identified from of the X-ray diffraction patterns that the secondary phase formed in grain boundaries decreased the piezoelectric properties. According to the substitution of PNN, the crystal structure of ceramics is transformed gradually from a tetragonal to rhombohedral phase. The x=0.10 mol PNN-substituted PMW-PNN-PZT-BF ceramics sintered at $920^{\circ}C$ showed the optimum values of piezoelectric constant($d_{33}$), piezoelectric figure of merit($d_{33{\cdot}}g_{33}$), planar piezoelectric coupling coefficient($k_p$) and density : $d_{33}=566$ [pC/N], $g_{33}=29.28[10^{-3}mV/N]$, $d_{33{\cdot}}g_{33}=16.57[pm^2/N]$, $k_p=0.61$, density=7.82 [$g/cm^3$], suitable for duplex ultrasonic sensor application.

• 한국전자통신학회논문지
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• 제8권9호
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• pp.1285-1291
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• 2013

본 논문에서는 광대역 특성을 갖는 이중 원형 링 모노폴 안테나를 설계 및 제작 하였다. 제안된 안테나는 평면형 모노폴 형태를 기본으로 이중 원형 링과 접지면으로 구성되어 있으며 광대역 특성을 갖도록 설계하였다. 최적화된 파라메타을 얻기 위해 상용 툴(HFSS)을 사용하여 시뮬레이션 하였으며 안테나 성능에 민감하게 적용받는 파라메타를 찾아내서 최적화된 수치를 얻었다. 얻어진 최적화된 수치를 사용하여 제안된 안테나를 제작하였다. 제작된 안테나는 광대역 특성을 갖는 대역에서 반사손실, 이득, 방사패턴의 특성을 측정하였다. 측정결과, -10dB을 기준으로 4,530 MHz(2,510-7,040 MHz)의 광대역 특성을 얻었으며 주어진 이득은 최대이득 0.71~3.38 dBi 그리고 평균이득 -3.85~0.3 dBi을 얻었다. 측정된 방사패턴의 경우, 전체적으로 E면은 전방향성의 방사패턴을 갖고 있으면 H면은 다이폴 안테나의 전형적인 특성을 나타내고 있다

• 한국음향학회지
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• 제40권1호
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• pp.10-17
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• 2021

심벌 트랜스듀서는 Class V flextensional 트랜스듀서의 소형화된 버전으로서 크기에 비해 낮은 공진 주파수와 고출력 특성을 가진다. 하지만, 높은 품질계수와 낮은 에너지 변환 효율성 때문에 단일보다는 배열형으로 많이 사용된다. 배열형으로 사용하면 구성 트랜스듀서들 간의 상호작용으로 인해 단일 트랜스듀서에 비해 주파수 특성에 많은 변화가 나타난다. 본 연구에서는 이러한 성질을 이용하여 심벌 어레이가 광대역 특성을 가지게 하는 패턴을 설계하였다. 특정 중심 주파수를 가지는 세 개의 심벌 트랜스듀서를 먼저 설계하였고, 설계된 심벌 트랜스듀서들로 3 × 3 평면 배열을 구성할 수 있는 모든 패턴을 찾았다. 그 후, 이들 패턴들의 주파수 특성을 분석하고, 그 결과를 바탕으로 높은 비대역폭을 구현하기 위해 가장 효과적인 배열 패턴을 도출하였다. 도출된 배열 패턴은 기준 모델에 비해 비대역폭이 최대 24.9 % 개선되었다.

• Journal of the korean society of oceanography
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• 제33권3호
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• pp.71-79
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• 1998

Silty tidal rhythmites were found from the upper Pleistocene sequence unconformably overlain by the Holocene tidal deposits within the macrotidal coastal zone of Youngjong Island, western coast of Korea. The rhythmites occur as vertically accreted, parallel and planar laminae that are 0.1-2.5 mm in thickness. Each lamina grades from coarse silt (mean grain size: 5-6.5 ${\phi}$) at the lower part into fine silt to mud (mean grain size: 6-7.5 ${\phi}$) at the upper part. The rhythmites can be classified into two types based on the patterns in laminar thickness variation. Type I is a bundle of 12-20 laminae in which laminar thickness varies sinusoidally. Type ll is an alternation of thick and thin laminae as a couplet. Type I is inferred as a product of varying tidal energy during a semimonthly (neap-spring) tidal cycle, in which thicker laminae were deposited during spring tides and thinner laminae were formed during neap tides. Type ll is interpreted to have been formed by asymmetric semidiurnal tidal currents in association with diurnal inequality, whereby thick lamina of each couplet represents dominant tidal current and the thin lamina reflects subordinate tidal current.