• Structural Monitoring and Maintenance
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• 제7권1호
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• pp.1-12
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• 2020

Railway tracks are the direct supporting structures of the trains, which are vulnerable to produce large deformation under the temperature stress or subgrade settlement. The health status of track is critical, and the track should be routinely monitored to improve safety, lower the risk of excess deformation and provide reliable maintenance strategy. In this paper, the distributed optical fiber sensor was proposed to monitor the continuous deformation of the track. In order to validate the feasibility of the monitoring method, two deformation monitoring tests on one steel rail model in laboratory and on one real railway tack in outdoor were conducted respectively. In the model test, the working conditions of simply supported beam and continuous beam in the rail model under several concentrated loads were set to simulate different stress conditions of the real rail, respectively. In order to evaluate the monitoring accuracy, one distributed optical fiber sensor and one fiber Bragg grating (FBG) sensor were installed on the lower surface of the rail model, the strain measured by FBG sensor and the strain calculated from FEA were taken as measurement references. The model test results show that the strain measured by distributed optical fiber sensor has a good agreement with those measured by FBG sensor and FEA. In the outdoor test, the real track suffered from displacement and temperature loads. The distributed optical fiber sensor installed on the rail can monitor the corresponding strain and temperature with a good accuracy.

• 센서학회지
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• 제24권1호
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• pp.1-5
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• 2015

The V-grooved single-mode fiber in which a surface part of the core was removed was investigated as a quasi-distributed water detection sensor. In the normal state, the V-grooved region is filled and covered with a specific RI (Refractive Index)-matched medium, and the sensor experiences minimal optical loss. As water invades the V-grooved region, the material is dissolved and removed, and a considerable optical loss occurs owing to the large RI difference between the fiber core and water. The experimental results showed the feasibility of the device as a sensor element of the quasi-distributed water detection sensor system based on general optical time domain reflectometry (OTDR).

• 센서학회지
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• 제22권4호
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• pp.297-301
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• 2013

We proposed and demonstrated a distributed fiber-optic overheating detection sensor using optical time domain refrectometry. With increased of temperature the optical fiber is bended by a bi-metal and it result in optical leaky loss of the fiber. The sensor structure is designed in such a way that the signal of overheating is happen when the temperature exceeding a threshold temperature and the optical fiber is protected from excess bending.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.505-510
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• 2002

We have focused on the development of a fiber optic BOTDA (Brillouin Optical Time Domain Analysis) sensor system in order to measure temperature distributed on large structures. Also, we present a feasibility study of the fiber optic sensor to monitor the distributed temperature on a building construction. A fiber optic BOTDA sensor system, which has a capability of measuring the temperature distribution, attempted over several kilometers of long fiber paths. This simple fiber optic sensor system employs a laser diode and two electro-optic modulators. The optical fiber of the length of 1400 m was installed on the surfaces of the building. The change of the distributed temperature on the building construction was well measured by this fiber optic sensor. The temperature changed normally up to 4℃ through one day.

• 센서학회지
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• 제23권4호
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• pp.229-233
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• 2014

In this study, a V-grooved single-mode fiber along with optical time domain reflectometry (OTDR) as a quasi-distributed temperature sensor was investigated. The external medium used to fill the V-groove affects the optical mode. The V-groove was filled with ethylene vinyl acetate (EVA) because its transmittance was sensitive to temperature. The experimental results showed that the optical loss of the sensor varies with temperature, and the sensitivity depends on the depth of the V-groove.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.792-796
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• 2003

In this paper, to detect external sound frequency on the latticed structure, fiber optic sensor net using Sagnac interferometer was fabricated and tested. The latticed structure fabricated with dimension of 50cm in width and 50cm in height, the optical fiber, 50m in length, distributed and fixed on the latticed structure. Single mode fiber, a laser with 1,550nm in wavelength, 2${\times}$2 coupler were used. External sound signal applied to the fiber optic sensor net and the detected optical signals were compared and analyzed to the detected microphone signals against time and frequency domain. Based on the experimental results, fiber optic sensor net using Sagnac interferometer detected external sound frequency, effectively. This system can be expanded to the structural health monitoring system.

• 한국소음진동공학회논문집
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• 제14권7호
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• pp.569-576
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• 2004

In this paper, to detect external sound frequencies on the latticed structure, fiber optic sensor net using Sagnac interferometer was fabricated and tested. The latticed structure was fabricated with a dimension of 50 cm in width and 50 cm in height. The optical fiber of 50m in length was distributed and fixed on the surface of the latticed structure. Single mode fiber, a laser with 1,550 nm in wavelength, 2 ${\times}$ 2 coupler were used. External sound signal, 240 Hz, 495 Hz, 1.445 kHz, 2k Hz, applied to the fiber optic sensor net and the detected optical signals were compared to the detected microphone signals against time and frequency domains. Based on the experimental results, fiber optic sensor net using Sagnac interferometer detected external sound frequency, effectively. This system can be expanded to the structural health monitoring system.

• 한국광학회지
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• 제17권2호
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• pp.127-135
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• 2006

광주파수 변조된 펌프와 프로브 빛의 광섬유 내 중첩을 시간 영역에서 직접 다루는 방법으로 공간 선택적 브릴루앙 산란 방식의 분포형 광섬유 센서를 시뮬레이션 하였다. 광섬유 내 브릴루앙 이득 분포의 시간/공간적 변화를 구하였고, 이종 광섬유의 접속과 온도 분포가 존재하는 경우에 대해 시뮬레이션 하여 분포형 센서로서 합당한 결과를 얻었다. 변조 파형으로서 정현파 대신에 삼각파를 이용한 경우에 정현파에 비해 공간 분해능 면에서 유리한 것으로 나타났다.

• Smart Structures and Systems
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• 제20권1호
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• pp.75-83
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• 2017

Effectively monitoring the concrete cracks is an urgent question to be solved in the structural safety monitoring while cracks in hydraulic concrete structures are ubiquitous. In this paper, two experiments are designed based on the measuring principle of Pulse-Pre pump Brillouin Optical Time Domain Analysis (PPP-BOTDA) utilizing Brillouin optical fiber sensor to monitor concrete cracks. More specifically, "V" shaped optical fiber sensor is proposed to determine the position of the initial crack and the experiment illustrates that the concrete crack position can be located by the mutation position of optical fiber strain. Further, Brillouin distributed optical fiber sensor and preinstall cracks are set at different angles and loads until the optical fiber is fractured. Through the monitoring data, it can be concluded that the variation law of optical fiber strain can basically reflect the propagation trend of the cracks in hydraulic concrete structures.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.234-237
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• 2002

To detect external vibration signals on the latticed fence structure, distributed fiber optic sensor using Sagnac interferometer was fabricated and tested. The latticed structure fabricated with dimension of 170cm in width and 180cm in height, the optical fiber, 50m in length, distributed and fixed on the latticed structure. It was verified the sensitivity of the Sagnac interferometer using the PZT phase modulator. Fiber optic external vibration signal spplied to the latticed fence structure from 100Hz to several kHz. The interferometeric fiber optic sensor detected the excited vibration signal very effectively without any signal processing. The detected optical signals were compared and analyzed to the detected acclerometer signals.