• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.159-162
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• 2004

The processing of phenolic composite reinforced with hybrid of PAN based/Rayon based carbon fabrics using FBG sensor and thermocouple was studied. Once the composite is cured, the reflection spectrum from the FBG sensor shifted the center wavelength with an increase in the temperature. Also, the change in the form of the reflection spectrum obtained during the cooling process of the cure cycle was caused by the thermal shrinkage. During the curing process, uniform distribution of the temperature profile was observed throughout the sample.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1062-1067
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• 2007

This study presents an experimental technique to monitor the dynamic behavior of the railway bridge system simultaneously using multiplexed fiber Bragg grating (FBG) sensors. The measuring quantities include stains, curvatures, vertical deflections, and vertical accelerations. The strains are directly measured from multiplexed FBG sensors at various locations of the test bridge followed by curvature calculations based on the plane section assumption. Vertical deflections are then estimated using the Bernoulli beam theory and regression analysis. Finally, vertical accelerations are obtained from the numerical differentiation in time domain. In order to verify the proposed method, several conventional electric strain gauges, displacement transducers, and accelerometers are installed at the mid-span of the bridge for comparisons. A test train is passed over the bridge to monitor the dynamic response of the bridge. The monitoring results show that the multiplexed FBG sensing system is able to capture the essential behavior of the test bridge while resolving wiring problem in practice.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.14-17
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• 2003

Vibration control of a composite plate with a surface-bonded fiber Bragg grating (FBG) sensor and piezoceramic actuators has been performed using a neural network based adaptive predictive control algorithm. For the detection of Bragg wavelength changes, two cavity lengths in Fabry-Perot read-out interferometers are used in order to produce two quadrature phase shifted signals. The FBG sensor system and real-time neuro-adaptive control algorithm could be applicable to diverse dynamic systems.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.416-420
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• 2002

This Paper describes a matched-filter type strain sensor system using optical fiber Bragg grating (FBG) sensor. Matched-filter type uses another wavelength-matched FBG filter to track wavelength shift in the FBG sensor. Filter FBG is attached on a fiber stretcher and stretched by PZT actuator. To overcome the nonlinearity and hysteresis of the PZT actuator that degrades system accuracy, a string resonator which can measure an absolute strain is employed. And the effect of vibration modes on string resonator is investigated particularly regarding its sensitivity and stability.

• Current Optics and Photonics
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• v.4 no.3
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• pp.186-192
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• 2020

This paper describes a real-time monitoring system in Ethernet passive optical networks (EPON) that uses burst-mode fiber Bragg grating (FBG) optical sensors. The FBG interrogation unit in the optical line terminal (OLT) transmits the monitoring wavelength to optical network units (ONUs). The FBG sensor unit in each ONU returns a burst-mode monitoring signal to the OLT. As the system applies time division multiple access (TDMA), a uniform Bragg wavelength can be used to monitor the EPON system. The FBG interrogation unit analyzes the received burst-mode monitoring signals and outputs fault information on the ONU branches in EPON. The simulation results show the effectiveness of the proposed monitoring system based on TDMA. In addition, we compared the proposed TDMA-based monitoring system with a WDMA-based monitoring system.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.90.2-90.2
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• 2010

흙막이 굴착 및 절취사면의 보강공법으로 많이 적용되고 있는 앵커의 장력을 측정하는 전기저항식 로드셀과 스트레인게이지, 바이브레이팅 와이어 (vibrating wire) 타입의 모니터링 방법은 안전관리를 위한 장기적인 모니터링에 한계를 가지고 있어 이를 개선할 수 있는 방안으로 광섬유 센서를 이용하여 강연선의 변형률을 측정할 수 있는 스마트 텐던이 개발되었다(김재민 등, 2007). 앵커를 구성하는 7연 강연선(텐던)의 중앙케이블에 삽입된 광섬유브래그격자(Fiber Bragg Grating ; FBG)센서는 기존 스트레인게이지 타입에 비해 크기가 작고 내구성이 우수하며 전자기파에 의한 노이즈 발생이 없고 하나의 리드선으로 다중점 측정(multiplexing)이 가능하여 장기모니터링에 효과적인 장점이 있다. 본 연구에서는 FBG센서를 내장한 스마트 텐던을 실대형(Prototype) 앵커(L=11.5m)에 적용하여 현장 인발실험에 의해 시공중 장력 모니터링을 수행하고 로드셀 측정결과와 비교하였고 정착부에 설치된 FBG 센서로부터 앵커의 하중전이 계측을 수행하였다.

• Advanced Composite Materials
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• v.16 no.2
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• pp.115-134
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• 2007

This study proposes two new approaches for identifying damage patterns in a holed CFRP cross-ply laminate using an embedded fiber Bragg grating (FBG) sensor. It was experimentally confirmed that the reflection spectrum from the embedded FBG sensor was significantly deformed as the damage near the hole (i.e. splits, transverse cracks and delamination) extended. The damage patterns were predicted using forward analysis (a damage analysis and an optical analysis) with strain estimation and the proposed damage-identification method as well as the forward analysis only. Forward analysis with strain estimation provided the most accurate damage-pattern estimation and the highest computational efficiency. Furthermore, the proposed damage identification significantly reduced computation time with the equivalent accuracy compared to the conventional identification procedure, by using damage analysis as the initial estimation.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.238-244
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• 2000

FBGs have been extensively used as strain sensors or temperature sensors in a variety of applications related to composites because of embedding ability, small size and multiplexing capability. We inspected embedding environments inside composites with optical fiber by microscope analysis and birefringence characteristics of FBG embedded into textile composite laminate by cure monitoring using a high power WSFL. The cure monitoring of the cases with the striped FBG and the recoated FBG provided comprehensive understandings about the birefringence effect induced by the transverse stress. And these results allowed to consider a recoating method as an important tool to relieve birefringence.

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.105-110
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• 2007

A tunable band-pass filter of fiber Bragg gratings incorporating the Sagnac loop interferometer configuration is presented. The proposed band-pass filter with extinction ratio 20 dB has practical advantages in terms of price and performance in comparison with the conventional band-pass filter using a circulator.

• Journal of Sensor Science and Technology
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• v.15 no.4
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• pp.251-256
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• 2006

This paper describes the flexible force sensor using fiber Bragg grating (FBG) and silicone rubber for the tactile sensation to detect the distributed normal force. The newly designed FBG flexible force has simple structure and can be easily multiplexed with simple wiring compared with the other electric mechanical sensors. We designed the flexible silicone rubber transducer and found the optimum embedding position of FBG in the transducer using the finite element analysis. This flexible force sensor has good performance and is immunity to the electromagnetic field compared with any other kinds of small force sensors for tactile sensation.