Force Sensor Based on FBG Embedded in Silicone Rubber

Force sensing is a key enabler for getting haptic feedback, useful in a variety of applications, especially in the fields of robotics, automation, and health. Indeed, equipping machines, vehicles, robots, and even humans with force sensors provides controlled processes and production, safe and enhanced external interaction, and capability to perform efficient manipulation and precise movements. Aiming to develop an alternative solution to electrical force sensors, in this work a fiber Bragg grating (FBG) is embedded inside a patch made of silicone rubber. Such embedding strategy allows to make the FBG sensitive to the force variations, obtain a flexible patch having a moldable shape, and protect the most fragile areas of the optical fiber. Moreover, due to its high flexibility and stretchability, the sensing patch can be easily employed as portable and wearable device. Besides reporting fabrication process and results of the performed force tests, this work provides a systematic study of the FBG embedding in a silicone matrix. Indeed, for this purpose, three sensing patches having different thicknesses are developed and tested in temperature, strain, and force, finding that the patch thickness influences the sensing performances of the device. The resulting force sensitivity varies in the range from 9.2 to 19.0 pm/N, based on the sensor thickness. Temperature sensitivity, instead, is comparable with respect to bare FBGs, while strain sensitivity is enormously reduced, obtaining a patch able to insulate the FBG from the strain variations.