• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.150-153
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• 2003

Longitudinal strains({$varepsilon}_x$) of the core and skin layers in glass fiber reinforced plastic(GFRP) cross-ply composite laminates have been studied using the embedded optical fiber sensor of totally-reflected extrinsic Fabry-Perot interferometer(TR-EFPI). Foil-type strain gauges bonded on both the upper and lower surfaces were used for the measurement of the surface strains. Both TR-EFPI sensor and strain gauge bonded on the specimen surface showed excellent agreement within -0.0086 ~ +0.0302% strain. It was shown that values of {$varepsilon}_x$ in the interior of the surface layer and the core layer measured by embedded TR-EFPI sensor was significantly higher than that of the specimen surface measured by strain gauges. The experimental results were ascertained with finite element analysis. Embedded TR-EFPI optical fiber sensor could measure accurately the internal strains which were different from the surface.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.133-138
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• 2003

As concrete structures are heated, thermal strain can be developed. Because of the boundary conditions, the thermal stress may be arisen. Thermal strain and temperature were measured simultaneously using an optical fiber sensor. Fiber Bragg Grating Sensor(FBG sensor) was used in the measurement. Because it can measure the strains more than two points with one line, it was possible to measure both thermal strain and temperature with one line. To compare data measured by FBG sensor, strain and temperature were measured using strain gauge and thermocouple. The FBG sensor could measure the strain under the temperature greater than $60^{\circ}C$ but strain gauge couldn't. Both the FBG temperature sensor and thermocouple could measure the temperature and the results are related each other linearly.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.397-404
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• 1999

It is essential to measure load transfer mechanism of pile to check the appropriateness of assumptions made for design purpose and to continuously monitor the behavior of pile foundation. Through many attempts to monitor the behavior of super-structure in civil engineering area using several optical fiber sensors have been made, application of optical fiber sensor technology on pile foundation has not been tried up to now. Load transfer of model piles during compression loading was measured by optical fiber sensors and compared with the measurement by strain gauges. Fiber Bragg Grating(FBG) sensor system was used since it has many advantages, such as easy multiplexing, high sensitivity, and simple fabrication. Besides the model pile tests, uniaxial tension test of steel bar and compression tests of mortar specimen were carried out to evaluate the performance of FBG sensors in embedded environments. The shift of refilming wavelength due to the strain in FBG sensor is converted to the strain at sensor location and the dependence between them is 1.28 pm/${\mu}$ strain. FBG sensors embedded in model pile showed a better survivability than strain gauges. Measured results of load transfer by both FBG sensors and strain gauges were similar, but FBG sensors showed a smoother trend than those by strain gauge. Based on the results of model pile test, it was concluded that the use of FBG sensor for strain measurement in pile has a great potential for the analysis of pile load transfer.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.184-189
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• 2000

Two types of fiber-optic sensors, EFPI(extrinsic Fabry-Perot interferometer) and FBG(fiber Bragg grating), have been investigated for measurement of thermal strain and temperature. The EFPI sensor is only for measurement of thermal strain and the FBG sensor is for simultaneous measurement of thermal strain and temperature. FBG temperature sensor was developed to measure strain-independent temperature. This sensor configuration consists of a single-fiber Bragg grating and capillary tube which makes it isolated from external strain. This sensor can then be used to compensate for the temperature cross sensitivity of a FBG strain sensor. These sensors are demonstrated by embedding them into a graphite/epoxy composite plate and by attaching them on aluminum rod and unsymmetric graphitelepoxy composite plate. All the tests were conducted in a thermal chamber with the temperature range $20-100^{\circ}C$. Results of strain measurements by fiber-optic sensors are compared with that from conventional resistive foil gauge attached on the surface.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.3
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• pp.39-44
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• 2004

Fiber Bragg grating sensors are fabricated by core index modulation using UV laser and phasemask. Bragg wavelength of the grating is changed by the external strain. In this paper, a signal processing system of fiber Bragg grating sensor has studied in the optical wavelength domain. The system is based on the sweep semiconductor light source that consists of SLD, F-P tunable filter and etalon filter. The hysteresis effects of PZT in the F-P tunable filter are compensated. The long term measurement stability is obtained by controlling the temperature of F-P tunable filter and the SLD. We compare the strain data from fiber Bragg grating sensor and that from strain gauge at concrete hume pipe. We also get very good results for the long gauge displacement using fiber Bragg grating sensor which are identical to the data with short gauge length ordinary displacement sensor.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.4
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• pp.363-370
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• 2020

This paper reports the results of an experimental study using the BOTDR sensor to detect the unbonded location of attached CFRP sheet for structural rehabilitation. A specimens with the unattached CFRP sheet were fabricated for this study, on which BOTDR sensor was attached with a nylon net. During the flexural test of the specimens, the strain of the CFRP sheet was measured using the BOTDR sensor and electric resistance gauges. From the results, it was confirmed that the strain distribution obtained through the BOTDR sensor can be effectively used to visualize and detect the unbonded position of the CFRP sheet. In addition, In addition, the strain measured by the BOTDR sensor was found to be more effective in analyzing the overall structure behavior than the electric resistance strain gauge. The development of a BOTDR sensor with a measuring longth of less than 100 mm will enable accurate detection of the local unbonded position of the CFRP sheet.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.393-398
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• 2008

With the substantial increase of the size of structure, management and monitoring of excavation for the foundation construction becomes more difficult. Therefore, massive collapses which are related to retaining wall recently increase. However, since the study on measuring and monitoring the pre-stressing force of anchor is insufficient, behavior of anchor may not be predicted and monitored appropriately by the existing strain gauge type monitoring system. FBG Sensor, which is smaller than strain gauge and has better durability and does not have a noise from electromagnetic waves, was adapted to develope a smart anchor. A series of pullout tests were performed to verify the feasibility of smart anchor and find out the load transfer mechanism around the steel wire fixed to rock with grout.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.505-510
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• 2008

FBG Sensor, which is smaller than strain gauge and has better durability and does not have a noise from electromagnetic waves, was adapted to develope a smart anchor. A series of pullout tests were performed to verify the feasibility of smart anchor and find out the load transfer mechanism around the steel wire fixed to rock with grout. Distribution of shear stresses at steel wire-grout interface is assessed from the measured strain distribution by the optical fiber sensors and compared with stress distributions predicted by Farmer's and Aydan's formulas. It was found that present theoretical formulas may underestimate the failure depth and magnitude of shear stresses when the pullout loads increase.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.4
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• pp.495-501
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• 2014

Piezoresistive-type, capacitive-type, and optical-type sensors have mainly been used for measuring a strain. However, in building a sensor network for remote monitoring using these conventional sensors there are disadvantages such as the complexity of a measuring system including wireless communication circuitry and high cost. In this paper, we demonstrates a highly-sensitive surface acoustic wave (SAW) strain sensor which is advantageous to harsh environments and wireless network. We designed and fabricated the SAW strain sensor. The SAW strain sensor attached on a specimen was tested with a tensile tester. The strain on the sensor surface was measured with a commercial strain gauge and compared with that obtained from strain analysis. The central frequency shift of the SAW sensor was measured with a network analyzer. The sensitivity of the SAW strain sensor is 134 $Hz/{\mu}{\varepsilon}$ which is high compared to previous results.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.1514-1518
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• 2009

Recently, railroad construction has been increased all over the world and as the train is getting high-speeded, there has been a need for guaranteed safety, so that a requirement for heath monitoring techniques for destruction that generated by gradually accumulated damages is now increasing. Especially the rail is crucial part that contact with wheel directly and delivers the train's load to a sleeper. It needs a technique that can guarantee a safety by sensing the possible cracks. In this paper, when train's load applied to the rail, strain distribution that introduced to entire length of rail is monitored using optical fibre. Optical fibre is used as a medium for measuring the strain and BOCDA (Brillouin Optical Correlation Domain Analysis) system is organized for measuring the distributed variation that implied to optical fibre. Optical fibre is attached at lower flange where tension is maximized when the load of train applied to the rail and strain gauge is implied together to compare the accuracy of measurement.