Wearable and Thermal Drift-Compensated Monitoring System Based on Fiber Bragg Grating Sensors for a 3D-Printed Foot Prosthesis

Monitoring foot prostheses is essential, as their performance impacts users’ daily lives. Fiber Bragg Grating (FBG) sensors represent a gold standard in monitoring applications, but traditional optoelectronic units are too cumbersome for wearable applications. This research addresses this issue by using a lightweight and compact optoelectronic unit and developing a compensation algorithm to overcome the signal drift phenomena caused by the light source instability. The proposed method uses an FBG as a reference to provide the algorithm with information on the signals drift. The developed algorithm is based on the assumptions of linearity among drift in different detection channels and the absence of drift at the initial time instant. The compensation variable was experimentally identified and validated. Experimental validation through temperature tests showed the algorithm reduces the drift error by 60%. Finally, mechanical tests were conducted on a foot prosthesis equipped with two FBGs: one used as a reference and the other for strain sensing. An electrical strain gauge was used to validate the FBG-based sensing system. The results of the mechanical tests indicate the possiblity to monitor a foot prosthesis using FBGs. The FBG and strain gauge measurements comparison aligns with previous studies where high-performance optoelectronic units were used.