• Title/Summary/Keyword: 격자 위상

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Measurement of Transverse Strain Using Polarization Maintaining Fiber Bragg Grating Sensor (편광 유지 광섬유 브래그 격자 센서를 이용한 횡방향 변형률 측정)

  • Yoon, Hyuk-Jin;Kim, Dae-Hyun;Hong, Chang-Sun;Kim, Chun-Gon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.6
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    • pp.30-35
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    • 2003
  • In this paper, the transverse strain was measured using polarization maintaining fiber Bragg grating(PMFBG) sensor. PMFBG sensor was fabricated using phase mask and Excidmer laser. The reflected wavelength of PMFBG sensor had dual peaks due to intrinsic birefringence. To find the polarization axes, peak sensitivity was measured under compression test. The signal characteristics of PMFBG sensor were also examined in embedding condition. The embedded PMFBG sensor in epoxy block was loaded for the transverse strain measurement, The wavelength-swept fiber laser(WSFL) was used to construct the PMFBG sensor system. Experiments showed that the PMFBG sensor could successfully measure the transverse strain.

Design and Analysis of Plasmonic Grating-Assisted Directional Coupler based on Silicon Waveguide (실리콘 도파로에 기초한 플리즈마 격자 구조형 방향성 결합기의 설계 및 분석)

  • Ho, Kwang-Chun
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.12 no.5
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    • pp.55-60
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    • 2012
  • Longitudinal transmission-line modal theory is applied to analyze maximum power transfer in plasmonic grating-assisted directional couplers (P-GADC) based on silicon waveguide. By defining a coupling efficiency amenable to rigorous analytical solutions and interference between even and odd modes, the power exchange of TE modes as a function of propagation distance is evaluated. The numerical result reveals that maximum power transfer occurs at a grating period ${\Lambda}_{eq}=10.26{\mu}m$, in which the insertion loss of supermodes is equal to each other. That is, it is generally different from conventional phase-matching condition or minium gap condition of GADC.

Structural Layout Design for Concrete Structures Based on the Repeated Control Method by Using Micro Lattice Truss Model (마이크로 격자트러스모델을 이용한 반복강성제어법에 의한 콘크리트 구조형태의 최적화)

  • Choi, Ik-Chang;Ario, Ichiro
    • Journal of the Korea Concrete Institute
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    • v.20 no.6
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    • pp.705-712
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    • 2008
  • This study carried out simulation for structural layout design for concrete structures by using the models of the ground structure method. The micro lattice truss is modeled as assemblage of a number of unit cells. The progress of analysis repeat to undergo finite element analysis to feed-back results of stress to the stiffness of each member. Through the repeated this analysis, truss model is represented to form the topological materials and the structural shape with the use of the local stress condition without mathematical optimum tools. It is successful to analyse the shape-layout problem as numerical samples on the lattice truss model.

Failure detection of composite structures using a fiber Bragg grating sensor (광섬유 브래그 격자 센서를 이용한 복합재 구조물의 파손 검출)

  • 고종인;김천곤;홍창선
    • Composites Research
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    • v.17 no.2
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    • pp.28-33
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    • 2004
  • Failure detection in a cross-ply laminated composite beam under tensile loading were performed using a fiber Bragg grating (FBG) sensor. A Passive Mach-Zehnder interferometric demodulator was proposed to enhance sensitivity and bandwidth. The proposed FBG sensor system without active device such as a phase modulator is very simple in configuration, easy to implement and enables the measurement of high-frequency vibration with low strain amplitude such as impact or failure signal. Failure signals detected by a FBG sensor had offset value corresponding to the strain shift with vibration at a maximum frequency of several hundreds of kilohertz. at the instant of transverse crack propagation in the 90 degree layer of composite beam.

Influence of the random fluctuation in grating period on the Coupling Coefficient of QWS-DFB Lasers (회절격자 주기의 랜덤 변이가 QWS-DFB 레이저의 정규화된 결합계수에 미치는 영향)

  • Ha, Seon-Yong;Kim, Sang-Bae
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.38 no.9
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    • pp.624-633
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    • 2001
  • Influence of the grating half-period fluctuation on the normalized coupling coefficient has been studied by an effective index transfer matrix method in quarter wavelength shifted(QWS) DFB lasers. The laser facets are assumed to be perfectly antireflection coated, and the period fluctuation is modeled by two correlated Gaussian random variables. In the presence of the random fluctuation in the grating period, effective normalized coupling coefficient is reduced because the in-phase feedback strength Is weakened. We have shown that the normalized coupling coefficient determined from the side mode spacing is less than the effective coupling coefficient, and the normalized coupling coefficient determined from the mode spacing or spontaneous emission spectrum does not properly represent the feedback strength of the grating.

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The characteristics of tilted grating in depressed- and step- index fiber and its application (Depressed index type과 Step index type 광섬유에서의 경사진 브래그격자 특성과 응용)

  • 권서원;이상배;최상삼;박진우
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.35D no.12
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    • pp.83-91
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    • 1998
  • Fiber Bragg grating which has a blazed ang1e to the plane of incident wave generates a side-mode as well as main-mode. The side-mode has an identical characteristics with a long period grating that couples with a cladding mode, so rejects the special wavelength. We experimented on the side-mode characteristics with two fibers which Ge doped depressed index fiber and very high photosensitive H$_2$ loaded step index fiber according to the tilted angle. Also, using a phase mask equipped with rotation plate which has 0.02$^{\circ}$ resolution, we can control the bandwidth and the peak value of a total loss spectrum by aligned tilted grating in a fiber and using this, tried to compose the ASE band rejection filter of the Erbium doped fiber amplifier.

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Precise Tidal Simulation on the Yellow Sea and Extended to North Western Pacific Sea (황해 및 북서태평양 확장해역 정밀조석모의)

  • Suh, Seung-Won;Kim, Hyeon-Jeong
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.23 no.3
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    • pp.205-214
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    • 2011
  • Finite element grid refinements with different intensities having 14 K, 52 K and 211 K on the Yellow Sea (YS) have been constructed to make precise tidal simulations. In the meanwhile 57 K grid was made to the extended North Western Pacific (NWP) sea. Numerical simulation were done based on 32 parallel processors by using pADCIRC v 49.21 model. In the YS tidal simulation on YS-G52K and YS-G211K grid structure, KorBathy30s and ETOPO1 bathymetry data are used and 4 major tidal constituents are prescribed from FES2004. Computed results are in good agreement within 0.138 meter in RMS error for amplification and 14.80 degree of phase compared to observed tidal records. Similar error bounds are acquired in the extended NWP tidal simulation on NWP-G57K grid with 8 tidal constituent prescription on the open boundary.

Suppression of side lobe and grating lobe in ultrasound medical imaging system (의료용 초음파 영상 시스템에서 부엽과 격자엽의 억제)

  • Jeong, Mok Kun
    • The Journal of the Acoustical Society of Korea
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    • v.41 no.5
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    • pp.525-533
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    • 2022
  • We propose an effective method for suppressing both side and grating lobes by applying 2-dimensional Fourier Transform to the received channel data during the receive focusing process of an ultrasound imaging system. When the signal from the image point is focused, the channel signals have the same DC value across the channels. However, even after echoes from outside an imaging point are focused, they are manifested as having different spatial frequencies depending on their incident angles. Therefore, after the receive focusing delay time is applied, 2-D Fourier Transform is performed on the time-channel data to separate the DC component and other frequency components in the spectral domain, and the weighting value is defined using the ratio of the two values. The side lobe and grating lobe were suppressed by multiplying the ultrasound image by a weighting value. Ultrasound images with a frequency of 5 MHz were simulated in a 64-channel linear array. The grating lobe appearing in the ultrasound image was completely removed by applying the proposed method. In addition, the side lobe was reduced and the lateral resolution was greatly increased. Results of computer simulation on a human organ mimicking image show that the proposed method can aid in better lesion diagnosis by increasing the image contrast.

Research on the development of rainfall and flood disaster information production technique using microwave precipitation observation station: case study of Samcheok area (전파강수관측소를 활용한 강우 및 홍수 재해정보 생산 기술 개발 연구: 삼척지역 사례연구)

  • Yoon, Seong Sim;Lim, Sanghun;Kim, Hyunjung;Jeong, Hyeon Gyo
    • Proceedings of the Korea Water Resources Association Conference
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    • 2020.06a
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    • pp.203-203
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    • 2020
  • 동해안에 위치한 영동지역은 산지로 둘러싸여 있어 지형적인 여건으로 지상강우관측망의 밀도가 낮으며, 지상관측소의 관측한계를 보완하기 위해 사용되고 있는 기존 대형 레이더는 지형 차폐로 인해 영동지역에서는 정확한 강우정보를 관측하기 어렵다. 강우정보는 홍수예측을 위해 필수적인 정보이므로, 집중호우와 태풍으로 인한 홍수재해가 빈번히 발생하는 영동지역에서는 관측공백의 해소가 필요하다. 이를 위해 환경부에서는 동해안 지역에 2기의 전파강수관측소를 설치, 운영 중에 있다. 해당 관측소 자료는 30km 관측반경 범위 내에서 수 백 미터 이하의 격자 강우자료를 생산할 수 있는 장점이 있다. 본 연구에서는 전파강수관측소의 자료를 강우 및 홍수 재해정보 생산에 활용하고자 한다. 대상지역은 영동지역에 위치한 삼척오십천으로 해당 지역은 친수적으로 조성되어 강우로 인한 시민의 인명피해가 위험이 존재하는 곳이다. 본 연구에서는 새로 설치된 삼척 전파강수관측소로 관측된 자료를 이용하여 고해상도 격자 및 유역평균강우정보를 생산하고, 지역특성을 반영하여 강우정보 기반으로 하천홍수 위험을 판단할 수 있는 하천흐름계산도표를 개발하여 평가하고자 한다. 생산된 고해상도 격자 강우자료는 70m 격자 해상도를 갖으며, 분포형 비차등위상차를 이용하여 추정된 강우정보이다. 유역평균강우는 삼척오십천 유역과 삼척시 동단위 행정구역별로 산출된다. 또한 하천흐름계산도표는 삼척오십천 유역의 현장답사를 통해 시민의 접근성, 하천수위 급상승으로 인한 피해가능성을 고려하여 6개 지점을 선정하여 개발하고, 전파강수관측소 관측강우정보를 활용하여 홍수예측정보로의 적절성을 평가한다.

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Measurement of three dimensional shapes using phase-shifting shadow moire method (위상 이동 그림자 무아레 방법을 이용한 3차원 형상의 측정)

  • 강영준
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.6 no.4
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    • pp.39-45
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    • 1997
  • Shadow moire topography has been used as a noncontact method for measuring the 3-D shapes of objects. The moire fringes are results from the superposition of a master grating and its shadow projected on the surface of an object. But in case of the classical shadow moire method, in general, the resolution is a few tenths of millimeter. It is difficult to use a phase -shifting method in shadow moire because it is impossible to obtain uniform phase shifts on the whole field. But in this study , We introduce a phase-shifting method to improve the resolution of the classical shadow moire method. This method is based on the fact that if the depth of object is much less than the distance between the observer and the master grating, the phase shifts are almost uniform on the whole field area. Finally, we applied this new phase-shifting method to the measurement of the 3-D shape of a coin.

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