• Korean Journal of Optics and Photonics
• /
• v.30 no.6
• /
• pp.226-229
• /
• 2019

We investigated an interrogation system for fiber Bragg gratings by using a 50-GHz 96-channel array waveguide grating. Linearity of the sensitivity (the wavelength shift in response to the change in strain or temperature) is achieved for a Bragg grating of sufficiently wide bandwidth. The present wavelength-monitoring system could measure the change in Bragg wavelength with a resolution of 0.01 nm, at intervals of 10 seconds. When this interrogation system was used for a linear array of 12 acrylaterecoated fiber gratings, the wavelength sensitivity changed from 0.018 nm/℃ to 0.01 nm/℃ when the operating temperature changed from -25℃ to 85℃.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.3A
• /
• pp.257-264
• /
• 2010

Generally, estimations on the displacement as an important factor in evaluating the safety of large structures could be a barometer assessing whether the condition of the structure is deteriorating. Practically, it is not easy how to measure the displacement response to large structures like suspension bridges. In this study, as a method for estimation displacement response from strain signals, mode decomposition technique is proposed. Total displacement response is estimated by superposing quasistatic displacement response and modal displacement responses in dominant modes with larger contributions after estimating the modal displacement responses. If foiled strain gauges are used to measure strain signals, there would likely to generate electric noise, what's more, the more measuring points there are the more economic burden it could be. In order to solve such problems, fiber optic bragg-grating(FBG) sensors were used, which have multi-point measurements with no effect on electric noises. Therefore, the experiment was performed through dynamic load test of suspension bridge and plate-girder bridge to review the possibility for using mode decomposition technique.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.36 no.6
• /
• pp.443-450
• /
• 2016

In this study, we propose a novel fiber optic sensor to show the measurement feasibility of distributed temperature and strains in a single sensing fiber line. Distributed temperature can be measured using optical time domain reflectometry (OTDR) with a Raman anti-Stokes light in the sensing fiber line. Moreover, the strain can be measured by fiber Bragg gratings (FBGs) in the same sensing fiber line. The anti-Stokes Raman back-scattering lights from both ends of the sensing fiber, which consists of a 4 km single mode optical fiber, are acquired and inserted into a newly formulated equation to calculate the temperature. Furthermore, the center wavelengths from the FBGs in the sensing fiber are detected by an optical spectrum analyzer; these are converted to strain values. The initial wavelengths of the FBGs are selected to avoid a cross-talk with the wavelength of the Raman pulsed pump light. Wavelength shifts from a tension test were found to be 0.1 nm, 0.17 nm, 0.29 nm, and 0.00 nm, with corresponding strain values of $85.76{\mu}{\epsilon}$, $145.55{\mu}{\epsilon}$, $247.86{\mu}{\epsilon}$, and $0.00{\mu}{\epsilon}$, respectively. In addition, a 50 m portion of the sensing fiber from $30^{\circ}C$ to $70^{\circ}C$ at $10^{\circ}C$ intervals was used to measure the distributed temperature. In all tests, the temperature measurement accuracy of the proposed sensor was less than $0.50^{\circ}C$.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.4A
• /
• pp.605-609
• /
• 2006

In this study, two kinds of smart accelerometers are investigated for the application of smart sensors to the structural health monitoring of infrastructures. Smart optical Fiber Bragg Grating (FBG) type and Micro-Electo-Mechanical System (MEMS) type accelerometers are selected for this study and the high sensitive ICP type accelerometer is used for the reference sensor. Small size shaking table tests were performed with 3-story shear building model using random input ground motions. The output only modal identification was carried out using stochastic subspace identification and the performances of sensors are compared in modal domain indirectly. The modal sensitivity method was applied to update the story stiffness of numerical model and the updated results were verified using the additional experiments for the same structure with additional mass.

• Smart Structures and Systems
• /
• v.20 no.4
• /
• pp.441-450
• /
• 2017

The objective of this work is to present a conceptual design and the modelling of a distributed sensor system based on fiber optic devices (Fiber Bragg Grating, FBG), aimed at measuring span-wise and chord-wise variations of an adaptive (morphing) trailing edge. The network is made of two different integrated solutions for revealing deformations of the reference morphing structure. Strains are confined to typical values along the span (length) but they are expected to overcome standard ranges along the chord (width), up to almost 10%. In this case, suitable architectures may introduce proper modulations to keep the measured deformation low while preserving the information content. In the current paper, the designed monitoring system combines the use of a span-wise fiber reinforced patch with a chord-wise sliding beam. The two elements make up a closed grid, allowing the reconstruction of the complete deformed shape under the acceptable assumption that the transformation refers to regular geometry variations. Herein, the design logic and some integration issues are reported. Preliminary experimental test results are finally presented.

• Journal of Korean Association for Spatial Structures
• /
• v.8 no.6
• /
• pp.95-100
• /
• 2008

The object of this paper is to verify possible to monitor the deformation of cable in the tensegrity structure. Also, always monitoring system of tensegrity structure using Fiber Bragg Grating Sensor is described. We carry out experiments with measuring deformation of cable in the tensegrity structure based on loading conditions. In the result of experiment, the Fiber Bragg Grating Sensors shows accurate response to the loading conditions. Therefore, we can make sure the possibility of Fiber Bragg Grating Sensor in health monitoring of the cable structure like tensegrity structure.

• Smart Structures and Systems
• /
• v.3 no.4
• /
• pp.475-494
• /
• 2007

This paper deals with the development of an innovative distributed construction system based on smart prefabricated concrete elements for the real-time condition assessment of civil infrastructure. So far, two reduced-scale prototypes have been produced, each consisting of a $0.2{\times}0.3{\times}5.6$ m RC beam specifically designed for permanent instrumentation with 8 long-gauge Fiber Optic Sensors (FOS) at the lower edge. The sensing system is Fiber Bragg Grating (FBG)-based and can measure finite displacements both static and dynamic with a sample frequency of 625 Hz per channel. The performance of the system underwent validation in the laboratory. The scope of the experiment was to correlate changes in the dynamic response of the beams with different damage scenarios, using a direct modal strain approach. Each specimen was dynamically characterized in the undamaged state and in various damage conditions, simulating different cracking levels and recurrent deterioration scenarios, including cover spalling and corrosion of the reinforcement. The location and the extent of damage are evaluated by calculating damage indices which take account of changes in frequency and in strain-mode-shapes. The outcomes of the experiment demonstrate how the damage distribution detected by the system is fully compatible with the damage extent appraised by inspection.

• Proceedings of the KSR Conference
• /
• 2008.06a
• /
• pp.109-117
• /
• 2008

In this study, a method predicting the displacement responseof structures from the measured dynamic strain signal is proposed by using a mode decomposition technique. Dynamic loadings including wind and seismic loadings could be exerted to the bridge. In order to examine the bridge stability against these dynamic loadings, the prediction of displacement response is very important to evaluate bridge stability. Because it may be not easy for the displacement response to be acquired directly on site, an indirect method to predict the displacement response is needed. Thus, as an alternative for predicting the displacement response indirectly, the conversion of the measured strain signal into the displacement response is suggested, while the measured strain signal can be obtained using fiber optic Bragg-grating (FBG) sensors. To overcome such a problem, a mode decomposition technique was used in this study. The measured strain signal is decomposed into each modal component by using the empirical mode decomposition(EMD) as one of mode decomposition techniques. Then, the decomposed strain signals on each modal component are transformed into the modal displacement components. And the corresponding mode shapes can be also estimated by using the proper orthogonal decomposition(POD) from the measured strain signal. Thus, total displacement response could be predicted from combining the modal displacement components.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.13 no.1
• /
• pp.223-235
• /
• 2021

The Vortex-Induced Vibration (VIV) test system on deepwater riser based on Bare Fiber Bragg Grating (BFBG) sensor technology was designed. Meanwhile, a riser VIV response numerical model was established based on the work-energy principle. The results show that the first-order vibration frequency dominates the vibration of the riser, and as the velocity increases, the dominant frequency of the riser gradually increases under the effect of different top tensions. At the same velocity, as the top tension increases step by step, the dominant frequency and fatigue damage at the same position along the axial length of the riser both gradually decreases. The model test and numerical simulation show a relatively consistent change, maintaining a high degree of agreement. The process control system based on BFBG of model test has excellent performance, and FBG sensors have great advantages in VIV test of a vertical riser in water.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.20 no.1
• /
• pp.161-166
• /
• 2016

We studied the effect of $Co^{60}$ gamma-radiation on the FBGs by a variation of grating the fabrication parameters. The FBGs were fabricated in a different UV KrF laser intensity using the same boron co-doped photo-sensitive fiber and exposed to gamma-radiation up to a dose of 33.8 kGy. According to the experimental data and analysis results, We confirmed that the laser intensity for grating inscription has a highly effect on the radiation sensitivity of the FBGs and the radiation-induced Bragg wavelength shift by the change of laser process condition showed a difference more than about 30 %.