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. 2010;10(11):10105-27.
doi: 10.3390/s101110105. Epub 2010 Nov 10.

Feasibility of fiber Bragg grating and long-period fiber grating sensors under different environmental conditions

Jian-Neng Wang  1 , Jaw-Luen Tang
Affiliations

Feasibility of fiber Bragg grating and long-period fiber grating sensors under different environmental conditions

Jian-Neng Wang et al. Sensors (Basel). 2010.

Abstract

This paper presents the feasibility of utilizing fiber Bragg grating (FBG) and long-period fiber grating (LPFG) sensors for nondestructive evaluation (NDE) of infrastructures using Portland cement concretes and asphalt mixtures for temperature, strain, and liquid-level monitoring. The use of hybrid FBG and LPFG sensors is aimed at utilizing the advantages of two kinds of fiber grating to implement NDE for monitoring strains or displacements, temperatures, and water-levels of infrastructures such as bridges, pavements, or reservoirs for under different environmental conditions. Temperature fluctuation and stability tests were examined using FBG and LPFG sensors bonded on the surface of asphalt and concrete specimens. Random walk coefficient (RWC) and bias stability (BS) were used for the first time to indicate the stability performance of fiber grating sensors. The random walk coefficients of temperature variations between FBG (or LPFG) sensor and a thermocouple were found in the range of -0.7499 °C/ [square root]h to -1.3548 °C/ [square root]h. In addition, the bias stability for temperature variations, during the fluctuation and stability tests with FBG (or LPFG) sensors were within the range of 0.01 °C/h with a 15-18 h time cluster to 0.09 °C/h with a 3-4 h time cluster. This shows that the performance of FBG or LPFG sensors is comparable with that of conventional high-resolution thermocouple sensors under rugged conditions. The strain measurement for infrastructure materials was conducted using a packaged FBG sensor bonded on the surface of an asphalt specimen under indirect tensile loading conditions. A finite element modeling (FEM) was applied to compare experimental results of indirect tensile FBG strain measurements. For a comparative analysis between experiment and simulation, the FEM numerical results agreed with those from FBG strain measurements. The results of the liquid-level sensing tests show the LPFG-based sensor could discriminate five stationary liquid-levels and exhibits at least 1,050-mm liquid-level measurement capacity. Thus, the hybrid FBG and LPFG sensors reported here could benefit the NDE development and applications for infrastructure health monitoring such as strain, temperature and liquid-level measurements.

Keywords: 07.05.-t; 07.60.Vg; 42.81.-i.; fiber Bragg grating (FBG); finite element model; liquid-level; long-period fiber grating (LPFG); nondestructive evaluation (NDE); random walk coefficient; temperature, strain.

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Figures

Figure 1.
Figure 1.
Schematic of experimental setup of (a) a reference dual-wavelength grating FBG sensing system for temperature and strain measurements; (b) an LPFG sensing system either for temperature or liquid-level measurements.
Figure 1.
Figure 1.
Schematic of experimental setup of (a) a reference dual-wavelength grating FBG sensing system for temperature and strain measurements; (b) an LPFG sensing system either for temperature or liquid-level measurements.
Figure 2.
Figure 2.
3-D Surface plot of (a) strain variation and (b) temperature variation of simultaneous strain and temperature measurements within the temperature range 30–120 °C and strain range of 0–1,500 με.
Figure 3.
Figure 3.
FBG and LPFG sensors bonded on the surface of infrastructure materials: (a) a cylindrical concrete specimen; (b) an asphalt mixture specimen.
Figure 4.
Figure 4.
Indirect tensile test of an asphalt specimen with a packaged FBG sensor: (a) experimental setup; (b) asphalt mixture specimen.
Figure 5.
Figure 5.
Schematic of experimental setup for liquid-level sensor constructed by cascading five different wavelength LPFGs.
Figure 6.
Figure 6.
Modeling of an asphalt cylindrical specimen subjected to an indirect tensile load: (a) geometry plot for FBG sensing with loading strips; (b) normal mesh for asphalt specimen and strips.
Figure 7.
Figure 7.
Responses of temperature fluctuation tests using FBG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 7.
Figure 7.
Responses of temperature fluctuation tests using FBG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 8.
Figure 8.
Responses of temperature fluctuation tests using LPFG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 8.
Figure 8.
Responses of temperature fluctuation tests using LPFG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 9.
Figure 9.
Responses of temperature stability tests using FBG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 9.
Figure 9.
Responses of temperature stability tests using FBG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 10.
Figure 10.
Responses of temperature stability tests using LPFG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 10.
Figure 10.
Responses of temperature stability tests using LPFG sensor surface-bonded on (a) a cylindrical asphalt mixture specimen; (b) a cylindrical concrete specimen.
Figure 11.
Figure 11.
Plots of (a) vertical displacements; (b) horizontal displacements; and (c) horizontal normal strains of an asphalt specimen subjected to a 294-N load.
Figure 12.
Figure 12.
Comparison of FBG strain measurements with three different FEM modeling results.
Figure 13.
Figure 13.
Transmission spectra of a liquid-level sensor constructed by cascading five LPFGs with different resonant wavelengths: (a) Nos. 1–2 immersed in water; (b) Nos. 1–5 immersed in water.
Figure 13.
Figure 13.
Transmission spectra of a liquid-level sensor constructed by cascading five LPFGs with different resonant wavelengths: (a) Nos. 1–2 immersed in water; (b) Nos. 1–5 immersed in water.
Figure 14.
Figure 14.
Average wavelength shifts and corresponding standard deviations by performing five times liquid-level tests (Nos. 1–5 immersed in water).
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