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

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.

Femtosecond FBG Written through the Coating for Sensing Applications

“…The type I FBG breaking stress value of 5.3 GPa is higher than a previously reported value of 4.6 GPa for a commercial type I FBG written in silica fibers [ 25 ]. However, in [ 25 ], the chemical composition of the fiber is different and the FBGs were uncoated for UV writing purpose. This may explain the observed difference.…”

“…The type II gratings, at 0.5 GPa of mean breaking stress, has better mechanical strength than type I grating undergoing annealing treatment at 900 °C (mean breaking stress of 0.1 GPa [ 25 ]), which is the usual temperature for regenerated grating [ 25 ]. The type I FBG breaking stress value of 5.3 GPa is higher than a previously reported value of 4.6 GPa for a commercial type I FBG written in silica fibers [ 25 ]. However, in [ 25 ], the chemical composition of the fiber is different and the FBGs were uncoated for UV writing purpose.…”

Temperature Resistant Fiber Bragg Gratings for On-Line and Structural Health Monitoring of the Next-Generation of Nuclear Reactors

“…One approach to fix these FBG sensors to metallic substrate in order to perform strain measurement at high temperature is to bond these transducers using high temperature resistant adhesives. More sophisticated approaches may be to use metal-coated FBG and to braze them to the metallic structure or to directly embed the FBGs into a metallic substrate thanks to additive layer manufacturing processes [ 38 , 39 ].…”

Overview of high temperature fibre Bragg gratings and potential improvement using highly doped aluminosilicate glass optical fibres

“…An approach to attach these FBG sensors, especially to metallic substrates, is to bond them using high temperature resistant adhesives. More sophisticated approaches may be to directly embed the FBGs into a metallic substrate thanks to additive layer manufacturing processes [21,22] or to use metal-coated FBGs and to braze them to the metallic structure. Although of extreme importance, these topics are vast and go beyond the scope of this overview.…”