• 한국수자원학회논문집
• /
• 제47권1호
• /
• pp.37-47
• /
• 2014

본 연구에서는 하폭의 주기적인 변화에 의하여 교호사주와 복렬사주가 발생하는 수리학적 조건에서 주기적인 하폭변화에 의한 강제사주의 형성과정과 거동 특성을 2차원 수치모형을 이용하여 파악하였다. 하폭변화의 진폭이 크면, 사주의 파장은 짧아지고, 사주의 이동성은 크게 감소하였다. 교호사주가 발생할 수 있는 영역에서는 하폭의 변화에 대하여 강제효과가 크게 작용하며, 복렬사주가 발생할 영역에서는 하폭의 변화에 의한 강제효과가 상대적으로 작은 특성을 보여주었다. 복렬사주가 발달한 조건에서는 하도변화의 진폭 대 평균하폭의 비인 무차원 진폭이 0.25로 증가할 때 사주의 이동속도는 증가하지만, 이보다 크면 사주의 이동속도가 급격하게 감소하였다. 교호사주가 발생하는 조건에서는 사주의 파장 대하폭 변화의 파장 비인 무차원 사주의 파장이 증가할수록 사주의 이동속도가 증가하지만, 무차원 사주의 파장이 1에 가까운 경우에 사주의 이동속도가 급격하게 감소하였다. 즉, 사주의 파장과 하폭의 파장이 일치할 때, 하폭변화에 의한 강제효과가 강하게 작용하여 사주가 압박되기 때문이다.

• 한국수자원학회논문집
• /
• 제51권4호
• /
• pp.313-322
• /
• 2018

Step의 높이는 하상재료 입경의 크기와 거의 같은 상관관계가 있으며, 하도경사에 따라 증가하고, 하도 폭과 step 파장은 거의 같은 크기로서 하도경사가 증가하면 step 파장은 감소하는 것으로 분석되었다. 하도 폭과 step 폭은 뚜렷한 상관관계가 있으며, 하도 폭의 증가에 따라 step 폭도 증가하는 것으로 분석되었다. 또한, step 파장은 하도 폭에 의하여 규모가 정해지고, step 높이는 step을 형성하는 암석의 크기에 의해 지배되기 때문에 step-pool의 종단면의 하상구조는 하도경사에 따라 변화하는 것으로 판단된다. Pool의 규모는 하도 폭, 입경 및 하도경사와 상관성이 큰 것을 확인하였다. 따라서 하천의 step-pool 구조 특성은 다양한 인자들의 영향을 받지만 대표적으로 입경, 하도 폭 및 하도경사로서 설명할 수 있는 것으로 분석되었다.

• 한국전자파학회:학술대회논문집
• /
• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
• /
• pp.376-379
• /
• 2003

In this raper, proposed easy half-wavelength LPF and acceptor structure in actuality manufacture using EBG (Electromagnatic Bandgap) structure for application of micro-strip circuit. Because conventional half-wavelength LPF and acceptor is narrow line-width of High impedance, actuality manufacture is difficult. Width that in proposed structure narrow microstrip line of High impedance EBG structure use and has equal impedance embodied to wide microstrip line. Also, it is seen that actuality manufacture is available applying to half-wavelength LPF that have cut-off Frequency of 3GHz.

• Journal of electromagnetic engineering and science
• /
• 제12권1호
• /
• pp.26-31
• /
• 2012

We have proposed a metamaterial lens that enables sub-wavelength focusing, which is shorter than an operating wavelength. Our lens is a two dimensional array of a unit cell consisting of a metallic dual-plate printed on a dielectric substrate. The unique dual-plate structure provides negativeness both in permittivity and permeability, with no help from conventional additional structures, which are normally printed on the opposite of metallic patterns. Therefore, we can focus a source (or an image) in a tiny distance shorter than the free space wavelength (${\lambda}$) at the frequencies of interest. Furthermore, since the proposed geometry does not need separate supplementary structures to acquire negative permittivity or permeability, our lens is much simpler than conventional metamaterial lenses, which is a strong point in practical applications. We have validated sub-wavelength focusing ability in a 6 GHz frequency band through an experiment of near field scanning, which provided the width of about 0.19 ${\lambda}$ at a half maximum of a peak value of an measured image. The width of the focused image through the lens is more than 4 times shorter than that without the lens, which confirms the validity of our design approach.

• Wind and Structures
• /
• 제29권1호
• /
• pp.33-41
• /
• 2019

The interaction of head waves with an infinite row of identical, equally spaced, rectangular breakwaters is investigated in the presence of uneven bottom topography. Using linear water wave theory and matched eigenfunction expansion method, the boundary value problem is transformed into a system of linear algebraic equations which are numerically solved to know the velocity potentials completely. Utilizing this method, reflected and transmitted wave energy are computed for different physical parameters along with the wave field in the vicinity of breakwaters. It is observed that the wave field becomes more complicated when the incoming wavelength becomes smaller than the channel width. A critical ratio of the gap width to the channel width, corresponding to the inflection point of the transmitted energy variation, is identified for which 1/3 of the total energy is transmitted. Similarly, depending on the incident wavelength, there is a critical breakwater width for which a minimum energy is transmitted. Further, the accuracy of the computed results is verified by using the derived energy relation.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2002년도 ITC-CSCC -1
• /
• pp.542-544
• /
• 2002

This paper proposes a wavelength sensor based on the optical directional coupler. The finite-difference time-domain (FDTD) is used in analysis of the field intensity of tile light propagating thorough the structure. The device with tile width of 0.4 $\mu\textrm{m}$ and the thickness of 0.4 $\mu\textrm{m}$, which corresponding with the coupling length of 40$\mu\textrm{m}$, would provide tile linear relationship between the coupling efficiency against the wavelength. The device can sense the wavelength in a range between 1.5$\mu\textrm{m}$ and 1.6$\mu\textrm{m}$, with continuous resolution. The wide wavelength could be also done be paralleling th light to a number of wavelength-sensing modules with particularly required bands. Therefore, it could be employed as the wavelength sensing for most optical communications, optoelectronics, laser applications and etc.

• 대한전자공학회논문지
• /
• 제23권2호
• /
• pp.264-268
• /
• 1986

A thchnique has been studied for the measurement of the spectral loss and the cut-off wave length, at which the first high-order mode disappears. The near-field patterns of a fiber which is excited by a variable wavelength source are used for the measurement of cut-off wavelength. Because of the absorptive phenomenon of OH- molecular vibration, spectral loss of a single mode optical fiber sample is 5.6dB/km at 1380 nm wavelength and 1dB/km at 1240 nm wavelength. From the near field intensity patterns and the mode field diameter graph for the half power width, the cut-off wavelength of the fiber is measured to be 1120 nm.

• Applied Science and Convergence Technology
• /
• 제24권6호
• /
• pp.257-261
• /
• 2015

We report on GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) that can cover the spectral range of $3.6-25{\mu}m$. One advantage of the GaAs QWIPs is the wavelength tenability as a function of their structural parameters. We have performed a systematic calculation on the detection wavelength of a typical $GaAs/Al_xGa_{1-x}As$ multi-quantum-well photodetector, with the aluminum mole fraction (x) of $Al_xGa_{1-x}As$ barrier in the range of 0.15-0.43 and the quantum-well width range from 30 to 60 $60{\AA}$. Design and fabrication of a QWIP based on $GaAs/Al_{0.23}Ga_{0.77}As$ structure with $37{\AA}$-thick well width has been carried out. The calculated operation wavelength of the QWIP is in a good agreement with the experimental data taken by photo response and activation energy calculation from thermal quenching of integrated photoluminescence.

• 산업기술연구
• /
• 제28권B호
• /
• pp.235-238
• /
• 2008

In this paper, we have developed wavelength swept laser system for the swept source optical coherence tomography(SS-OCT). A laser is constructed by using the two SOAs parallel configuration, fiber Fabry-Perot tunable filter(FFP-TF). The wavelength sweeps are repetitively generated with the repetition period of 50Hz. The wavelength tuning range of the laser is more than FWHM of 80nm centered at the wavelength of 1310nm and the line-width of the source is 0.12 nm.

• 한국광학회지
• /
• 제10권6호
• /
• pp.512-517
• /
• 1999

이완발진 현상을 이용하는 단공진기 색소레이저(QDL:quenched dye laser)는 극단펄스 광원으로서 많은 장점을 갖고 있다. 본 연구에서는 파장 590nm에서 발진 스펙트럼의 최대값을 갖는 Rhodamine 6G를 레이저 매질로 하고, 파장 308nm의 XeCl 레이저를 펌핑원으로 하여, 이득의 길이가 5mm인 QDL의 이완발진에 의한 극단펄스 발생특성을 컴퓨터 시뮬레이션에 의해 분석하였다. 분석결과, 펌핑광의 펄스폭에 대하여 QDL 출력빔은 1/100 이하로 그 펄스폭이 짧아짐을 밝혀 QDL 이 극단펄스 발생용으로 매우 유용한 레이저임을 밝혔으며, 펌핑광의 공간적 크기를 조절함에 의하여 출력 펄스폭의 연속적인 가변동작이 가능함을 제시하였다.