• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.74-77
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• 2006

A scanned Fabry-Perot(F-P) filter and a Multi-Channel Wavelength Locker(MCWL) were used to interrogate fiber Bragg grating sensor array. When the F-P filter scans over the MCWL which works as a multi-reference the temporal peaks profiles correspond to the locking wavelengths. To solve the linearity, stability, and accuracy problems caused by the nonlinear response of F-P filter, a polynomial fitting algerian was used to calculate the relationship between the peak locations and the wavelengths in all the scanning range. Then from the reflected peaks locations and the best fitting line, the Bragg wavelengths can be obtained. The measurement linearity was greatly enhanced with wavelength resolution of about 4 pm in 10Hz scanning frequency.

• Smart Structures and Systems
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• v.19 no.6
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• pp.625-631
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• 2017

In the fields of civil engineering and seismology, it is essential to detect and tracking the vibrations, and the fiber Bragg gratings (FBGs) are typically used as sensors to measure vibrations. Where, one of the most popular and detailed approaches to use FBGs as vibration sensors involves the use of cantilever beam designs, which adds a mass to measure low and moderate frequencies (from 20 Hz up to 1 kHz) with high sensitivities (greater than 10 pm/g). The design consists of a bending strain in the cantilever that is simultaneously transferred to the FBG, resulting in a shift in the wavelength that is proportional to the strain experienced by the cantilever. In this work, we present the experimental results of a vibration sensor design using a cantilever beam to generate an axial uniform strain in the FBG in-line with the vertical axis, which modifies the cantilever's natural frequency that allows the sensor to have a wide frequency broadband without losing sensitivity. This sensor achieved a sensitivity of about 339 pm/g and a natural frequency of 227.3 Hz. The presented design compared with the traditional cantilever beam-based FBG vibration sensors, has the advantages of a simple design for detection on vibration-sensitive structures and its physical parameters can be easily modified in order to satisfy the requirements of the desired vibration measurements.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.3
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• pp.241-247
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• 2015

Deflection and deformation occur easily in structures with long length, such as bridges and pipelines. Shape monitoring is required for ensuring their structural health. A fiber Bragg grating (FBG) sensor can be used for monitoring a large-scale structure because of its advantage of multiplexing. In this study, FBG sensors were used for monitoring a composite beam structure, and its strains were measured at multiple points. Thereafter, a shape estimation technique based on the strains was studied. Particularly, a three-dimensional shape estimation technique was proposed for accurate structural health monitoring. A simple experiment was conducted to verify the performance of the shape estimation technique. The result revealed that the estimated shape of the composite beam structure was in agreement with the actual shape obtained after the deformation of the specimen. Additionally, the deflection at a specific point was verified by comparing the estimated and actual deformations measured using a micrometer.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.235-239
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• 2005

In this research, we investigated the frequency characteristic of low-velocity impact induced damage signals on graphite/epoxy composite laminates using high-speed fiber Bragg grating(FBG) sensor system. Appling the FBG sensors to damage assessment, we need to study the response of FBG sensors as the damage signals of the different incident angles because FBG shows different directional sensitivity. In order to discriminate an impact induced damage signal from that of undamaged case, drop impacts with different energies were applied to the composite panel with different incident angle to the FBG sensor. Finally, detected impact signals were compared using frequency distributions of wavelet detail components in order to find distinctive signal characteristics of composites delamination.

• 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.

• Korean Journal of Optics and Photonics
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• v.26 no.2
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• pp.83-87
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• 2015

This study was focused on developing an optical sensor that monitors ultraviolet (UV) light. Recently, we proposed and demonstrated a novel, highly sensitive UV sensor based on a fiber Bragg grating (FBG). To ensure that the incident UV light is focused on the FBG surface, the sensor was coated with an azobenzene polymer material that acts as a UV-induced stretchable functional material, in combination with a cylindrical focal lens. In this study we have improved the sensitivity of the sensor by employing a cylindrical focal mirror as a curved reflector, to refocus the UV light passing through the FBG. We considered the performance of several different types of reflectors and chose the optimal radius of curvature for the reflector. Compared to the UV sensor without an auxiliary device, the sensitivity of the FBG sensor with a focal lens and a curved reflector was 15 times as high.

• Proceedings of the Korean Nuclear Society Conference
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• 2003.05a
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• pp.397-397
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• 2003

• 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

• Proceedings of the Optical Society of Korea Conference
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• 1996.09a
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• pp.83-83
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• 1996

• 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.