Influence of adhesive and application method on FBG temperature sensors for space applications

Fiber optic sensors are already used in many industries, such as oil & gas and infrastructure. However, optical solutions have recently been explored in the aerospace sector, and Fiber Bragg Gratings (FBGs) are the most relevant sensor type. FBG sensors are a growing market, with a projected market value growth in 2028 of $5167.4 million and a compound annual growth rate of 23.9 %. Their peculiar properties (small size, lightweight, immunity to electromagnetic fields, multiplexing capability, and fast response) can overcome many of the challenges presented by the space environment. Nonetheless, they are not common in aerospace applications. With the proper packaging, FBG sensors are suitable for many thermal and chemical sensing measurements. Furthermore, with suitable packaging, FBGs could be used in aerospace since they can reach cryogenic temperatures and have vacuum applications. In this work, the effects of the adhesive and the application method on the substrate for thermal sensing were examined in a vacuum in the -170 to 220°C temperature range. The campaign test was divided into three phases with different methodologies, analyzing the eventual disturb introduced by the bonding technique. When an effective strategy is adopted, the study confirmed that, in vacuum, FBG sensors could reach comparable results with traditional thermocouples at cryogenic temperatures. This, combined with the above-mentioned optical fiber advantages, proves FBG to be strategic for thermal testing in space.