Metal coating for enhancing the sensitivity of fibre Bragg grating sensors at cryogenic temperature

Abstract

Fibre Bragg grating (FBG) sensors that are immune to electromagnetic interference could advantageously perform cryogenic temperature monitoring in superconducting magnetic fields, but their intrinsic temperature sensitivity is quite poor and must be enhanced. In fact, the low thermal expansion coefficient of silica limits the temperature sensitivity of bare FBG sensors at cryogenic temperature. In this paper the possibility of improving the temperature sensitivity of FBG sensors by metal coating is investigated. Specifically, zinc and copper coating depositions are performed by the traditional electrowinning process, after aluminium pre-coating of the sensor. Coated FBG sensors are inspected by both optical and metallographic techniques. SEM metallographic investigations show that a homogeneous deposit is obtained, with good metal adhesion to the FBG sensor. Optical testing shows that the optical properties of the coated FBG sensors are slightly affected: aluminium pre-coating produces appreciable modification of the diffraction spectrum in both peak width and peak shift, while zinc coating produces a moderate peak shift and copper coating just enlarges the peak width. Results presented in this paper show that both metals appreciably increase the temperature sensitivity of the FBG sensors. Zinc coating provides the highest sensitivity and high-resolution temperature measurements are possible at temperatures as low as 15 K.

Cryogenic Fiber Optic Sensors Based on Fiber Bragg Gratings

“…Zinc [2] and lead [3] metals have been shown to have very high expansion coefficients over the cryogenic temperature range. There are still problems with the stability and physical robustness of this technique, but the data offers the prospect of an FBG sensor that could be used in low temperature superconducting magnets.…”

A Review of Fiber Optic Technology for Turbine Engine Instrumentation Channel: Control, PHM, and Test Cell Applications

“…Given appropriate coatings and/or packaging, optical fiber sensors fare relatively well in both cryogenic [71] and elevated temperature [54] environments including those encountered in aerospace, nuclear reactor, geothermal [73] and thermal protections system (TPS) [1], [52]- [54], [76] applications. Figure 12 shows an example setup for temperature monitoring with an FBG array in a TPS tile subjected to heat from one side as may be the case for a re-entry vehicle.…”

Metal Embedded Optical Fiber Sensors: Laser-Based Layered Manufacturing Procedures

“…Lupi et al coated FBGs with zinc and copper. They used electrowinning for the deposition of the metallic layer after precoating the fiber with aluminum [15]. Li et al have employed magnetron sputtering for titanium and nickel deposition on FBGs.…”

“…Li et al have employed magnetron sputtering for titanium and nickel deposition on FBGs. According to the literature, electrowinning, sputtering, electron beam evaporation, and electroplating techniques are methods that have been employed for the deposition of on-fiber titanium, silver, gold, platinum, zinc, lead, and copper films [15][16][17][18][19].…”