Smart Elastic Fabric Strip Encompassing Prestrained Fiber Bragg Grating Sensors

This article describes the creation and characterization of a smart elastic fabric strip that incorporates prestrained fiber Bragg grating (FBG) sensors. The fabric strip is 700-mm long and 60-mm wide, and a standard single-mode optical fiber with four cascaded and wavelength-division-multiplexed gratings is sewn onto the strip. Each FBG sensor is affixed to a specifically designed 3-D-printed pad in a prestrained manner, which permits the detection of both FBG traction and compression. Among three configurations, the design of the pad has been chosen following tensile tests. The sensitivity of the elastic fabric strip was measured, and it is found that there is a Bragg wavelength deviation of 12.2 pm per mm of textile elongation and 11.7 pm per mm in release. Validation tests are conducted to demonstrate the system sensitivity to compression: indeed, a negative Bragg wavelength shift compared with the rest position can be observed. Afterward, ten traction cycles are applied to the fabric strip to validate its ability to repeat measurements in a dynamic setting. In stretched position, the standard deviation of the Bragg wavelength shifts from all the cycles is 2.46 pm. Similarly, in the rest position, the standard deviation is 0.60 pm. Finally, tests are performed in the context of backbone monitoring, and results are analyzed for four backbone positions. These experiments pave the way to the use of the smart elastic band for the dynamic measurement of the backbone position of a patient.