• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.3
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• pp.211-216
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• 2016

In several industrial fields, epoxy resin is widely used as an adhesive for co-curing and manufacturing various structures. Controlling the manufacturing process is required for ensuring robust bonding performance and the stability of the structures. A fiber optic sensor is suitable for the cure monitoring of epoxy resin owing to the thready shape of the sensor. In this paper, a fiber Bragg grating (FBG) sensor was applied for the cure monitoring of epoxy resin. Based on the experimental results, it was demonstrated that the FBG sensor can monitor the status of epoxy resin curing by measuring the strain caused by volume shrinkage and considering the compensation of temperature. In addition, two types of epoxy resin were used for the cure-monitoring; moreover, when compared to each other, it was found that the two types of epoxy had different cure-processes in terms of the change of strain during the curing. Therefore, the study proved that the FBG sensor is very profitable for the cure-monitoring of epoxy resin.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.4
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• pp.1081-1085
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• 2008

To measure the curvature, in this paper, we investigate an optical curvature sensor based on the fiber Bragg gratings. We observed the variation of the Bragg resonant wavelength shift to measure the curvature change. From the experimental results, we knew that the Brags resonant wavelength shift was lineally increased with the increase of the curvature from $0\;m^{-1}$ to $10\;m^{-1}$. It's slope is about $8.8\;pm/m^{-1}$. On the other hand, the spectral reflection decreased with the increase of the curvature.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.4
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• pp.305-312
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• 2007

Among many types of light rail transits (LRT), the rubber-tired automated guide-way transit (AGT) is prevalent in many countries due to its advantages such as good acceleration/deceleration performance, high climb capacity, and reduction of noise and vibration. However, AGT is generally powered by high-voltage electric power feeding system and it may cause electromagnetic interference (EMI) to measurement sensors. The fiber optic sensor system is free from EMI and has been successfully applied in many applications of civil engineering. Especially, fiber Bragg grating (FBG) sensors are the most widely used because of their excellent multiplexing capabilities. This paper investigates a prestressed concrete girder bridge in the Korean AGT test track using FBG based sensors to monitor the dynamic response at various vehicle speeds. The serviceability requirements provided in the specification are also compared against the measured results. The results show that the measured data from FBG based sensors are free from EMI though electric sensors are not, especially in the case of electric strain gauge. It is expected that the FBG sensing system can be effectively applied to the LRT railway bridges that suffered from EMI.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.91-97
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• 2001

We present a fiber Bragg grating (FBG) sensor system for measuring static and high-speed dynamic strains with a resolution of about $5\mu$strain. This sensor system demodulates signals from the FBG sensor utilizing a compensated tunable narrow bandpass filter. We have placed a set of twelve FBGs to concrete specimen and measured its internal stress under various applied load conditions.itions.

• Proceedings of the Optical Society of Korea Conference
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• 1999.08a
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• pp.60-61
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• 1999

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.333-339
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• 1997

We fabricated a sensor head which consists of spliced different-diameter fiber gratings for discrimination between strain and temperature. Because the fibers were drawn from the same preform, their temperature characteristics were the same but not for strain sensitivities which are inversely proportional to fibers cross-sectional areas. In measurement range of 0-1500$\mu$strain and 20-10$0^{\circ}C$, we could obtain, by using the matrix calculation, the unknown physical quantities within 10% of calculation error compared with the micrometer and thermocouple values. To improve the strain measurement accuracy, we suggest a new, novel method which deploys an unbalanced fiber Mach-Zehnder interferometer. This new signal processing technique converts the strain information to interference signal amplitude variation, temperature-independently. we obtained measurement accuracy nearly 80 times better than that obtainable with the conventional optical spectrum analyzer usage.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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• pp.1160-1165
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• 2006

In this paper, the 2-dimensional uniaxial force sensors array is introduced to detect the distributed force using fiber Bragg gratings. Uniaxial force transducer was designed to avoid the chirping and micro bending which degrade the performance of the sensor. The Brags wavelength shift of the sensor was estimated using the finite element analysis. Using this uniaxial force sensor, the uniaxial force sensors array $(3{\times}3)$ was fabricated, and the Performance of this sensors array was evaluated. The Presented sensors may has very simple configuration and its wiring is very simple compared with any other force sensors arrays.

• Proceedings of the Optical Society of Korea Conference
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• 2009.02a
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• pp.221-222
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• 2009

이 논문에서는 기존의 FBG 광센서와는 달리 이중파장 구조를 갖는 FBG 센서를 제안하여 기 존의 FBG 센서가 측정할 수 있는 범위를 획기적 으로 증대시킴을 보이고자 한다. 고해상도의 광범 위한 지역 측정은 두 가지의 광대역 광원을 이용 하는 매트릭스 구조의 FBG를 이용해 구성하였으며, 두 광원을 사용하는 통합시스템은 도파로 열격자(AWG)로 구성되어 있다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.833-839
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• 2013

In this study, an experiment was performed to monitor the two-dimensional shape of a cantilever composite structure using fiber Bragg grating (FBG) sensors. To monitor the shape of a composite structure, a deflection equation developed by NASA was applied and a composite beam attached to three FBG sensors was used. In the experiment, the shape of the composite beam was successfully estimated and an error was evaluated by comparing a real deflection. The error increased with real deflection; therefore, it was compensated by using the linear relationship between the error and the real deflection. After compensating the error, the measured deflection shows good agreement with the real deflection. Finally, the experiment shows that the FBG sensor and the deflection equation are suitable for monitoring the deflection curve of the beam structure with compensation of the error.