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An Improved Metal-Packaged Strain Sensor Based on A Regenerated Fiber Bragg Grating in Hydrogen-Loaded Boron – Germanium Co-Doped Photosensitive Fiber for High-Temperature Applications

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ABSTRACT

Local strain measurements are considered as an effective method for structural health monitoring of high-temperature components, which require accurate, reliable and durable sensors. To develop strain sensors that can be used in higher temperature environments, an improved metal-packaged strain sensor based on a regenerated fiber Bragg grating (RFBG) fabricated in hydrogen (H2)-loaded boron–germanium (B–Ge) co-doped photosensitive fiber is developed using the process of combining magnetron sputtering and electroplating, addressing the limitation of mechanical strength degradation of silica optical fibers after annealing at a high temperature for regeneration. The regeneration characteristics of the RFBGs and the strain characteristics of the sensor are evaluated. Numerical simulation of the sensor is conducted using a three-dimensional finite element model. Anomalous decay behavior of two regeneration regimes is observed for the FBGs written in H2-loaded B–Ge co-doped fiber. The strain sensor exhibits good linearity, stability and repeatability when exposed to constant high temperatures of up to 540 °C. A satisfactory agreement is obtained between the experimental and numerical results in strain sensitivity. The results demonstrate that the improved metal-packaged strain sensors based on RFBGs in H2-loaded B–Ge co-doped fiber provide great potential for high-temperature applications by addressing the issues of mechanical integrity and packaging.

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Shift in the Bragg wavelength as a function of strain obtained from tensile tests at constant temperatures of 26.5 °C (a); 100 °C (b); 200 °C (c); 300 °C (d); 400 °C (e); 500 °C (f) and 540 °C (g). FE: finite element.
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sensors-17-00431-f009: Shift in the Bragg wavelength as a function of strain obtained from tensile tests at constant temperatures of 26.5 °C (a); 100 °C (b); 200 °C (c); 300 °C (d); 400 °C (e); 500 °C (f) and 540 °C (g). FE: finite element.

Mentions: To characterize the response to applied strain, the metal-packaged strain sensor based on the RFBG fabricated in H2-loaded PS1250/1500 fiber was mounted on the P91 steel specimen by spot welding. The specimen was loaded and unloaded at constant temperatures of room temperature (26.5 °C), 100 °C, 200 °C, 300 °C, 400 °C, 500 °C and 540 °C. Figure 9a–g illustrates the wavelength shifts of the metal-packaged RFBG strain sensor as a linear function of strains calculated from the applied forces, the cross-sectional area and Young’s modulus of the P91 steel specimen at the corresponding temperature (as listed in Table 1). The responses of the bare RFBG in H2-loaded PS1250/1500 fiber to the strains determined from the applied forces are also shown in Figure 9a–g for comparison. The observed shifts in Bragg wavelength and strains show linearity for both metal-packaged and bare RFBG sensors, with the adjusted coefficients of determination (adj R2) higher than 0.999 for the former and 0.9999 for latter. The metal-packaged sensor preserves its linear behavior implying a good interfacial integrity between every two layers and elastic deformations in each material. The strain sensitivities derived from the slope of the straight lines in Figure 9a–g are 2.10, 2.15, 2.12, 2.17, 2.15, 2.12 and 2.11 pm µε−1 for the metal-packaged RFBG sensor under loading at constant temperatures of room temperature (26.5 °C), 100 °C, 200 °C, 300 °C 400 °C, 500 °C and 540 °C, respectively, which is slightly higher than those of 2.08, 2.10, 2.08, 2.15, 2.04, 2.09 and 2.06 pm µε−1 under unloading, as elastic hysteresis occurs in the relatively flexible structural substrate. In addition, at corresponding test temperatures, the values are ~30% higher than the values of the metal-packaged strain sensor fabricated based on the RFBG in H2-loaded SMF-28 fiber reported in our previous work [17]. This could be mainly attributed to the differences in geometrical dimensions (the thickness of the electroplated nickel coating, the depth of the fiber embedded into the substrate, etc.) of the packaged structure fabricated manually, and inaccuracy in the material parameters (Young’s modulus, etc.) used to calculate the strains to which the steel specimen is subjected. The thinner coating of electroplated nickel and the deeper location of the fiber embedded into the substrate would result in the higher strain sensitivity of the sensors. The value of Young’s modulus for P91 steel used to calculate the strains to which the specimen is subjected may be slightly greater than the true value. Accordingly, the calculated strains are smaller than the true strains to which the P91 steel specimen is subjected, leading to the higher sensitivity that is the ratio of the wavelength shift to the calculated strain.


An Improved Metal-Packaged Strain Sensor Based on A Regenerated Fiber Bragg Grating in Hydrogen-Loaded Boron – Germanium Co-Doped Photosensitive Fiber for High-Temperature Applications
Shift in the Bragg wavelength as a function of strain obtained from tensile tests at constant temperatures of 26.5 °C (a); 100 °C (b); 200 °C (c); 300 °C (d); 400 °C (e); 500 °C (f) and 540 °C (g). FE: finite element.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5375717&req=5

sensors-17-00431-f009: Shift in the Bragg wavelength as a function of strain obtained from tensile tests at constant temperatures of 26.5 °C (a); 100 °C (b); 200 °C (c); 300 °C (d); 400 °C (e); 500 °C (f) and 540 °C (g). FE: finite element.
Mentions: To characterize the response to applied strain, the metal-packaged strain sensor based on the RFBG fabricated in H2-loaded PS1250/1500 fiber was mounted on the P91 steel specimen by spot welding. The specimen was loaded and unloaded at constant temperatures of room temperature (26.5 °C), 100 °C, 200 °C, 300 °C, 400 °C, 500 °C and 540 °C. Figure 9a–g illustrates the wavelength shifts of the metal-packaged RFBG strain sensor as a linear function of strains calculated from the applied forces, the cross-sectional area and Young’s modulus of the P91 steel specimen at the corresponding temperature (as listed in Table 1). The responses of the bare RFBG in H2-loaded PS1250/1500 fiber to the strains determined from the applied forces are also shown in Figure 9a–g for comparison. The observed shifts in Bragg wavelength and strains show linearity for both metal-packaged and bare RFBG sensors, with the adjusted coefficients of determination (adj R2) higher than 0.999 for the former and 0.9999 for latter. The metal-packaged sensor preserves its linear behavior implying a good interfacial integrity between every two layers and elastic deformations in each material. The strain sensitivities derived from the slope of the straight lines in Figure 9a–g are 2.10, 2.15, 2.12, 2.17, 2.15, 2.12 and 2.11 pm µε−1 for the metal-packaged RFBG sensor under loading at constant temperatures of room temperature (26.5 °C), 100 °C, 200 °C, 300 °C 400 °C, 500 °C and 540 °C, respectively, which is slightly higher than those of 2.08, 2.10, 2.08, 2.15, 2.04, 2.09 and 2.06 pm µε−1 under unloading, as elastic hysteresis occurs in the relatively flexible structural substrate. In addition, at corresponding test temperatures, the values are ~30% higher than the values of the metal-packaged strain sensor fabricated based on the RFBG in H2-loaded SMF-28 fiber reported in our previous work [17]. This could be mainly attributed to the differences in geometrical dimensions (the thickness of the electroplated nickel coating, the depth of the fiber embedded into the substrate, etc.) of the packaged structure fabricated manually, and inaccuracy in the material parameters (Young’s modulus, etc.) used to calculate the strains to which the steel specimen is subjected. The thinner coating of electroplated nickel and the deeper location of the fiber embedded into the substrate would result in the higher strain sensitivity of the sensors. The value of Young’s modulus for P91 steel used to calculate the strains to which the specimen is subjected may be slightly greater than the true value. Accordingly, the calculated strains are smaller than the true strains to which the P91 steel specimen is subjected, leading to the higher sensitivity that is the ratio of the wavelength shift to the calculated strain.

View Article: PubMed Central - PubMed

ABSTRACT

Local strain measurements are considered as an effective method for structural health monitoring of high-temperature components, which require accurate, reliable and durable sensors. To develop strain sensors that can be used in higher temperature environments, an improved metal-packaged strain sensor based on a regenerated fiber Bragg grating (RFBG) fabricated in hydrogen (H2)-loaded boron–germanium (B–Ge) co-doped photosensitive fiber is developed using the process of combining magnetron sputtering and electroplating, addressing the limitation of mechanical strength degradation of silica optical fibers after annealing at a high temperature for regeneration. The regeneration characteristics of the RFBGs and the strain characteristics of the sensor are evaluated. Numerical simulation of the sensor is conducted using a three-dimensional finite element model. Anomalous decay behavior of two regeneration regimes is observed for the FBGs written in H2-loaded B–Ge co-doped fiber. The strain sensor exhibits good linearity, stability and repeatability when exposed to constant high temperatures of up to 540 °C. A satisfactory agreement is obtained between the experimental and numerical results in strain sensitivity. The results demonstrate that the improved metal-packaged strain sensors based on RFBGs in H2-loaded B–Ge co-doped fiber provide great potential for high-temperature applications by addressing the issues of mechanical integrity and packaging.

No MeSH data available.


Related in: MedlinePlus