• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.130-138
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• 2002

수압실험 동안 광섬유 브래그 격자(FBG) 센서를 이용하여 필라멘트 와인딩된 복합재료 탱크의 변형률을 모니터링하였다. 20개의 FBG 센서와 20개의 스트레인 게이지를 복합재료 탱크의 돔과 실린더 부분에 부착하였다. 광섬유 센서를 위한 고출력 광원으로는 파장 이동 광섬유 레이저(WSFL)을 이용하였다. 실험결과로부터, 많은 수의 센서를 필요로 하는 대형 구조물의 건전성 모니터링에 FBG 센서 시스템이 유용함을 확인할 수 있었다.

• Composites Research
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• v.15 no.4
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• pp.32-36
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• 2002

Recently, the applications of composite materials become broader to civil engineering as well as mechanics and aerospace engineering. Cracks on the civil structures like bridges can cause stress concentration, which induces Peak splitting of fiber Bragg grating sensor and it makes strain measurements difficult. In this study, 4-point bending test of concrete beam with initial crack reinforced by composite patch was conducted in order to verify the effects of the stress concentration on the peak signal of FBG sensor and a novel method for signal maintenance.

• Structural Monitoring and Maintenance
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• v.5 no.1
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• pp.129-150
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• 2018

This paper presents the structural performance monitoring of an urban footbridge located in Hangzhou, China. The structural health monitoring (SHM) system is designed and implemented for the footbridge to monitor the structural responses of the footbridge and to ensure the structural safety during the period of operation. The monitoring data of stress and displacement measured by the fiber Bragg grating (FBG)-based sensors installed at the critical locations are used to analyze and assess the operation performance of the footbridge. A linear regression method is applied to separate the temperature effect from the stress monitoring data measured by the FBG-based strain sensors. In addition, the static vertical displacement of the footbridge measured by the FBG-based hydrostatic level gauges are presented and compared with the dynamic displacement remotely measured by a machine vision-based measurement system. Based on the examination of the monitored stress and displacement data, the structural safety evaluation is executed in combination with the defined condition index.

• Journal of the Optical Society of Korea
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• v.15 no.4
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• pp.329-334
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• 2011

We proposed a poly-dimethylsiloxane (PDMS)-coated fiber Bragg grating (FBG) temperature sensor for enhancing temperature sensitivity. By embedding the bare FBG in a temperature-sensitive elastomeric polymer, the temperature sensitivity of the proposed structure could be effectively improved by 4.2 times higher than those of the conventional bare-type FBG sensors due to the high thermal expansion coefficient of the PDMS. We analyzed the temperature-sensitivity enhancement effect with the increased Bragg wavelength shift in our structure and dependence on the temperature sensitivity with respect to the cross-section area of the PDMS.

• Current Optics and Photonics
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• v.2 no.1
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• pp.96-100
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• 2018

A tunable low-phase-noise microwave generation structure that utilizes an optoelectronic oscillator (OEO) and a fiber Bragg grating (FBG) is proposed and experimentally demonstrated in this article. This structure has no particular requirement for the band width of the laser, and its tunability is realized through adjusting the central frequency of the tunable FBG. A detailed theoretical analysis is established and confirmed via an experiment. A high-purity microwave signal with a frequency tunable from 6 to 12 GHz is generated. The single-sideband phase noise of the generated signal at 10.2 GHz is -117.2 dBc/Hz, at a frequency offset of 10 kHz.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.208-211
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• 2002

In RC beams strengthened with Epoxy-Bonded Fiber, debonding failure happens frequently. Moreover, through the life cycle, it is difficult to recognize clacks and deflections on the surface of concrete members strengthened with Epoxy- Bonded Fiber. For these reasons, we must always monitor the state of RC beams. The Optical FBG sensor is broadly accepted as a structural health monitoring device. The main objective of this paper is that it's possible to monitoring the debonding failure of R.C. beams strengthened with Epoxy-Bonded Fiber. For that, we fixed two Optical FBG sensors at the center of the beam and another two sensors in the end of Epoxy-Bonded Fiber, According to the comparison micro-strain between embeded sensor in concrete and that on the fiber surface, we can find the point which debonding failure occurs

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.326-331
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• 2009

An algorithm is proposed for computing dynamic displacements of a bridge using FBG sensors. An existing algorithm for estimating dynamic displacements of a simply supported beam through mode superposition is extended and applied to various types of bridges with bending and torsional modes. The proposed algorithm is examined through field tests on a suspension span steel deck plate box girder bridge. Guidelines are provided for determining the number of modes and the number of strain gages to be used.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.772-777
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• 2008

Recent development of fiber optic sensors and wireless sensor technology, made structural health monitoring of railway structures cost effective. In this paper, a micro bending fiber optic rail pad sensors are evaluated for train axle force measurement. In order to assess the usability of FBG fiber optic sensors for short-term bridge measurement, the FBG sensors and conventional strain gauges are installed at the same points and the strain results are compared. Also the impact factors are calculated using the FBG strain responses and the results are compared with the conventional sensor responses. A running KTX train was instrumented with wireless sensor system to measure the vibration characteristics and the results are compared with conventional wire sensor system.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.5
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• pp.80-87
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• 1999

We propose a new recirculating fiber delay-line filter structure. In proposed system, we insert a fiber Bragg grating(FBG) into a recirculating fiber delay line and it operates as a partially reflection mirror. Therefore, the transfer function of the system is given by the recirculating delay output part and the multiple-reflected output part due to a FBG. By adjusting the parameters such as coupling coefficient, reflectivity of FBG, and gain, we can make the system operate in various filter.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.71-76
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• 2006

In this paper, a long gauge Fiber Bragg Grating (FBG) sensor system is described and long gauge FBGs are well, suited for measuring the upper parts of the bridge piers under the extremely severe movement conditions. In the experiments, we used more than 30m long FBG sensors to measure the movement of top part of the bridge piers which are separated from the main bridge by cutting the decks. With the actuator, the deck and girders were pushed and released. We checked the movement of the top of the pier while releasing the pressure of the actuator with the long gauge fiber sensor. In order to measure the movement of the upper part of the pier, the reference point must be outside of the pier. Using the optical fiber sensors, one end of the sensor is attached to the top of the pier and the other end is attached to the bottom of the next pier. The fiber sensors showed good response to the release loading and we could calculate the movement of the top part of the pear.