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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

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.


Typical evolution of the reflection peak power and the Bragg wavelength shift of one grating with the corresponding temperature profile during annealing for fabrication of the regenerated fiber Bragg grating (RFBG) in H2-loaded PS1250/1500 fiber.
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sensors-17-00431-f001: Typical evolution of the reflection peak power and the Bragg wavelength shift of one grating with the corresponding temperature profile during annealing for fabrication of the regenerated fiber Bragg grating (RFBG) in H2-loaded PS1250/1500 fiber.

Mentions: Step 2: RFBGs were regenerated by annealing process. The type-I seed FBG was loosely placed in a capillary quartz tube (1 mm inside diameter and 2.5 mm outside diameter) horizontally inserted into the central area of a horizontal miniature tube furnace in order to maintain the temperature uniform along the grating and avoid any mechanical or thermal strain on the fiber. Then, a calibrated armored N-type thermocouple with a precision of ±0.5 °C was assembled together with the capillary quartz tube, and its tip was adjacent to the grating in order to control the temperature. It was built into the furnace’s feedback during the annealing throughout which the spectral behavior of the grating was monitored in reflection by a commercial FBG interrogator (Micron Optics, Inc., Sm125-500, Atlanta, GA, USA). The tabular furnace is custom-made with a length of 40 mm to anneal a short length of the fiber, as the mechanical strength of the fiber is considerably reduced by the annealing treatment and polymer coating is also removed via thermal stripping. Coating is essential to protect the fiber surface from handling damage during subsequent fabrication. The furnace is equipped with a quartz tube with an inside diameter of 8 mm and a length of 40 mm to homogenize the temperature inside the furnace. The furnace temperature was raised from room temperature to 500 °C within 50 min, and subsequently held constant at the temperature of 500 °C for ~120 min, which is the temperature triggering regeneration. To the best of the present authors’ knowledge, this temperature is the lowest regeneration temperature observed for the B–Ge co-doped photosensitive fiber, where a typical annealing process used for regeneration of RFBGs is shown in Figure 1. As the temperature approached 500 °C, the reflection peak power of the seed FBG started to decay drastically until it fell below the noise floor in a few minutes after the temperature reached 500 °C. After that, a regenerated grating appeared at longer wavelength after ~8 min at the temperature of 500 °C where the isothermal annealing was performed for ~120 min, followed by its reflection strength being increased gradually to a maximum until stability. No variation was observed in the strength of the RFBG as the temperature was decreased to room temperature over 90 min. The reflection spectra of the RFBG and its corresponding seed FBG was recorded at room temperature of 21 °C by the FBG interrogator.


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
Typical evolution of the reflection peak power and the Bragg wavelength shift of one grating with the corresponding temperature profile during annealing for fabrication of the regenerated fiber Bragg grating (RFBG) in H2-loaded PS1250/1500 fiber.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sensors-17-00431-f001: Typical evolution of the reflection peak power and the Bragg wavelength shift of one grating with the corresponding temperature profile during annealing for fabrication of the regenerated fiber Bragg grating (RFBG) in H2-loaded PS1250/1500 fiber.
Mentions: Step 2: RFBGs were regenerated by annealing process. The type-I seed FBG was loosely placed in a capillary quartz tube (1 mm inside diameter and 2.5 mm outside diameter) horizontally inserted into the central area of a horizontal miniature tube furnace in order to maintain the temperature uniform along the grating and avoid any mechanical or thermal strain on the fiber. Then, a calibrated armored N-type thermocouple with a precision of ±0.5 °C was assembled together with the capillary quartz tube, and its tip was adjacent to the grating in order to control the temperature. It was built into the furnace’s feedback during the annealing throughout which the spectral behavior of the grating was monitored in reflection by a commercial FBG interrogator (Micron Optics, Inc., Sm125-500, Atlanta, GA, USA). The tabular furnace is custom-made with a length of 40 mm to anneal a short length of the fiber, as the mechanical strength of the fiber is considerably reduced by the annealing treatment and polymer coating is also removed via thermal stripping. Coating is essential to protect the fiber surface from handling damage during subsequent fabrication. The furnace is equipped with a quartz tube with an inside diameter of 8 mm and a length of 40 mm to homogenize the temperature inside the furnace. The furnace temperature was raised from room temperature to 500 °C within 50 min, and subsequently held constant at the temperature of 500 °C for ~120 min, which is the temperature triggering regeneration. To the best of the present authors’ knowledge, this temperature is the lowest regeneration temperature observed for the B–Ge co-doped photosensitive fiber, where a typical annealing process used for regeneration of RFBGs is shown in Figure 1. As the temperature approached 500 °C, the reflection peak power of the seed FBG started to decay drastically until it fell below the noise floor in a few minutes after the temperature reached 500 °C. After that, a regenerated grating appeared at longer wavelength after ~8 min at the temperature of 500 °C where the isothermal annealing was performed for ~120 min, followed by its reflection strength being increased gradually to a maximum until stability. No variation was observed in the strength of the RFBG as the temperature was decreased to room temperature over 90 min. The reflection spectra of the RFBG and its corresponding seed FBG was recorded at room temperature of 21 °C by the FBG interrogator.

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.