Fabrication and thermal characteristics of multilayer metal-coated regenerated grating sensors for high-temperature sensing

Abstract

Health monitoring of components operating at high temperatures requires the development of new sensors to measure temperature and deformation. A regenerated grating (RG) sensor with titanium (Ti)–silver (Ag)–nickel (Ni) multilayer coatings is fabricated by magnetron sputtering and electroplating processes. Optical and thermal tests are performed to evaluate the characteristics of the Ti–Ag–Ni-coated RG sensor. The shapes of the reflection spectra for the RG are slightly affected by the metallization process. The Ti–Ag–Ni-coated RG sensor exhibits a higher sensitivity than that of the bare RG for temperatures up to 600 ° C, with good repeatability and stability. It is verified that the titanium coating can achieve good adhesion to the optical fiber and that the silver coating is suitable as a conductive layer for electroplating. An analytical model for the axial strain and radial strain in a multilayer metal-coated optical fiber is proposed. Comparisons of the experimental results and the theoretical predictions show a good agreement below 250 ° C. These results indicate that multilayer metal-coated RG sensors can be successfully fabricated by combining magnetron sputtering with electroplating and provide great potential for high-temperature sensing.

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

“…The behavior of the FBGs in H 2 -loaded PS1250/1500 fiber exhibiting two regeneration temperature regimes is very similar to that of the FBGs in H 2 -loaded GF1B fibers reported by Polz et al [35]. In contrast, for the FBGs in H 2 -loaded SMF28 fiber, only one regeneration regime above 900 °C was observed by the authors and other researchers [31,35]. Such behavior can be associated with the special type of fiber used.…”

“…In addition, the temperature measured with the N-type thermocouple is also shown in Figure 1. The behavior of the gratings in H 2 -loaded PS1250/1500 fiber is significantly different in comparison with that of the gratings in H 2 -loaded SMF-28 fiber whose behavior has been described in our previous work [31]. The type-I FBG in H 2 -loaded PS1250/1500 fiber started to slowly decay after the temperature exceeded 150 °C (corresponding to ~200 °C for FBG in H 2 -loaded SMF-28 fiber).…”

Evaluation of new regenerated fiber Bragg grating high-temperature sensors in an ISO 834 fire test

“…The convective heat transfer coefficient was defined as 25 W/(m 2 K), the emissivity of the exposed surface was defined as 0. 8 A different temperature curve was applied to each concrete specimen in the FEM defined by the temperature measured by the plate thermometer nearest to each specimen (PT2 for Specimen 1 and PT3 for Specimen 2). Plate thermometer temperature-time curves are shown in Figure 6.…”

“…In recent years several high temperature fiber optic sensors have been developed using different technologies such as chiral fiber gratings that were tested up to 1000 °C [6], sapphire gratings which measured maximum temperatures of 1745 °C [7] and multilayer metal-coated regenerated grating sensors that were calibrated for maximum temperatures of 600 °C [8]. However, all of these were tested in laboratory electric furnace tests and in conditions very different to those of real fire scenarios or to those of the standard tests used in fire engineering.…”

“…We consider these tests to be important since: (a) they enable the response of the sensor to direct flames to be evaluated in conditions similar to those of real fires; (b) they can detect possible problems associated with the installation of sensing systems similar to those found in monitoring actual building fires; and (c) the fire curves commonly used in fire engineering have extremely fast temperature increments, which were not considered in the tests conducted in electric furnaces reported in [6][7][8].…”