• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.31-36
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• 2003

Recently, composite materials are widely used for nozzle, pressure vessel, skins of satellite and many structures under condition of high temperature due to good thermal characteristics such as low CTE, heat-resistance, etc. Fiber optic sensors, especially FBG(fiber Bragg grating) sensors, can be a good counterproposal of strain gages for the measurement of material properties of composites under high temperature. In this research, T700/Epoxy specimens with embedded FBG sensors were fabricated and tested at the Instron with thermal chamber from room temperature to $400^{\circ}C$. The effects of embedding optical fiber on material properties were also verified. And, the experimental results were discussed and analyzed by microphotographs of the composite specimen.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.754-760
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• 2008

For monitoring of railway structures, optical fiber sensors are very convenient. The fiber sensors are very small and do not disturb the structural properties. They also have several merits such as electro-magnetic immunity, long signal transmission, good accuracy and multiplicity of one sensor line. Strain measurement technologies with fiber optic sensors have been investigated as a part of smart structure. In this paper, we investigated the possibilities of fiber optic sensor application to the monitoring of railway structures. We expect that the fiber optic sensors have much less noises than electrical strain gauges because of electro-magnetic immunity while railways operate electric power of 22000 volts. Fiber optic sensors showed good durability and long term stability for continuous monitoring of the railway structures as well as good response to the structural behaviors during construction.

• 센서학회지
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• 제15권3호
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• pp.179-185
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• 2006

We have developed a noncontact temperature sensor using a silver halides infrared optical fiber. An infrared radiation from a heat source is transferred by a silver halides infrared optical fiber and measured by infrared sensors such as a thermopile and a thermal optical power-meter. The relationships between the temperature of a heat source and the output voltage of the thermopile and the optical power of a thermal optical power-meter are determined. The measurable temperature range using a thermopile and a thermal optical power-meter are from 100 to $750^{\circ}C$ and from 30 to $750^{\circ}C$ respectively. It is expected that a noncontact temperature sensor using infrared optical fiber can be developed for medical and industrial usages based on the results of this study.

• Advanced Composite Materials
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• 제17권2호
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• pp.125-137
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• 2008

FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preforms before resin impregnation in VaRTM (Vacuum-assisted Resin Transfer Molding). The embedding location was the interface between the skin and the stringer in a CFRP-stiffened panel. The reflection spectra of the FBG sensors monitored the strain and temperature changes during all the molding processes. The internal residual strains of the CFRP panel could be evaluated during both the curing time and the post-curing time. The temperature changes indicated the differences between the dry preform and the outside of the vacuum bagging. After the molding, four-point bending was applied to the panel for the verification of its structural integrity and the sensor capabilities. The optical fibers were then used for the newly-developed PPP-BOTDA (Pulse-PrePump Brillouin Optical Time Domain Analysis) system. The long-range distributed strain and temperature can be measured by this system, whose spatial resolution is 100 mm. The strain changes from the FBGs and the PPP-BOTDA agreed well with those from the conventional strain gages and FE analysis in the CFRP panel. Therefore, the fiber-optic sensors and its system were very effective for the evaluation of the VaRTM composite structures.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2012년도 춘계학술대회
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• pp.564-567
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• 2012

광섬유는 신호를 전달하는 통신용 섬유, 물체를 관찰하기 위한 이미지 섬유, 각종 센서용 광섬유로서 원자력분야에서 사용된다. 특히 센서용 섬유로서 라만 산란광을 이용한 온도감지 섬유와 광섬유 브래그 격자을 이용한 온도/스트레인 섬유, 광자기효과를 이용한 광회전센서 섬유 등은 이미 실용화되어 있다. 그러나 광섬유에 방사선을 조사하면 색중심(color center)이 생성되어 광의 투과성이 크게 저하되고, 방사선 환경에서 적용의 제한이 있다. 본 논문에서는 고준위 방사선환경에 대한 광섬유 센서의 적용을 위한 연구로서 Ge가 함유된 일반단일모드 광섬유에 대한 감마선 조사에 따른 전송손실 특성 평가를 수행하였다. 시험에 사용된 방사선원은 $Co^{60}$ 감마선원으로, 총 4시간동안 0.5kGy/hr, 2kGy/hr, 8kGy/hr의 선량률(dose rate)로 조사하였다. 그 결과 감마선조사에 의한 단일모드 광섬유의 전송손실이 뚜렷하게 나타났고, 동일 누적선량에서 선량률이 클수록 전송손실이 증가하는 선량률 효과와 조사 후 광섬유의 전송손실이 클수록 손실 회복율이 증가하는 열화(annealing) 특성을 보였다. 본 시험결과는 향후 광섬유의 내방사화 연구의 기초자료로 활용할 계획이다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.17-20
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• 2005

In-situ structural health monitoring of filament wound pressure tanks were conducted during water-pressurizing test using embedded fiber Bragg grating (FBG) sensors. We need to monitor inner strains during working in order to verify the health condition of pressure tanks more accurately because finite element analyses on filament wound pressure tanks usually show large differences between inner and outer strains. Fiber optic sensors, especially FBG sensors can be easily embedded into the composite structures contrary to conventional electric strain gages (ESGs). In addition, many FBG sensors can be multiplexed in single optical fiber using wavelength division multiplexing (WDM) techniques. We fabricated a standard testing and evaluation bottle (STEB) with embedded FBG sensors and performed a water-pressurizing test. In order to increase the survivability of embedded FBG sensors, we suggested a revised fabrication process for embedding FBG sensors into a filament wound pressure tank, which includes a new protecting technique of sensor heads, the grating parts. From the experimental results, it was demonstrated that FBG sensors can be successfully adapted to filament wound pressure tanks for their structural health monitoring by embedding.

• 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).

• Current Optics and Photonics
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• 제5권6호
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• pp.652-659
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• 2021

The theoretical analysis and optimization of extrinsic Fabry-Perot interferometer (EFPI) opticalfiber humidity sensors are deeply investigated. For a typical dual-cavity structure composed of an optical fiber and a humidity-sensitive membrane (HSM), the changes in refractive index (RI) and initial length are discussed for polymer materials and porous oxide materials when relative humidity (RH) increases. The typical interference spectrum is simulated at different RH using MATLAB. The spectral change caused by changing HSM RI and initial length are simulated simutineously, showing different influences on humidity response. To deeply investigate the influence on RH sensitivity, the typical response sensitivity curves for different HSM lengths and air-cavity lengths are simulated. The results show that the HSM is the vital factor. Short HSM length can improve the sensitivity, but for HSM RI and length the influences on sensitivity are opposite, because of the opposite spectral-shift trend. Deep discussion and an optimization method are provided to solve this problem. According to analysis, an opaque HSM is helpful to improve sensitivity. Furthermore, if using an opaque HSM, a short air cavity and long HSM length can improve the sensor's sensitivity These results provide deep understanding and some ideas for designing and optimizing highly sensitive EFPI fiber humidity sensors.

• Journal of the Optical Society of Korea
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• 제3권2호
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• pp.69-73
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• 1999

This paper demonstrated the performance of a palladium wire hydrogen sensor based on a fiber Bragg grating as a means of developing a quasi-distributed hydrogen sensor network capable of operating at cryogenic temperatures. The new approach employing a fiber Bragg grating based palladium hydrogen sensor described in this study is advantageous over other traditional hydrogen sensors because of the multiplexing capability of fiber Bragg gratings. The sensitivity of the hydrogen sensor at room temperature is approximately 2.5 times that of the hydrogen sensor at cryogenic temperatures.

• Journal of the Optical Society of Korea
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• 제12권4호
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• pp.221-225
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• 2008

We propose a simple hydrogen detection scheme based on a Mach-Zehnder interferometer formed with a pair of palladium-coated long-period fiber gratings (LPGs). Since an LPG pair offered a fine-structured interference fringe in its transmission spectrum, the resolution as a sensor could be appreciably enhanced compared to that of a single LPG. As the palladium layer absorbed hydrogen, the effective refractive indices of the cladding modes were increased so that the interference spectrum was blue-shifted up to 2.3 nm with a wavelength sensitivity of -0.29 nm/min for 4% of hydrogen concentration.