A Stretchable, Skin-Adhesive FBG-Based Wearable Sensor for Human Health Monitoring: From Vital Signs to Biomechanical Activity

Wearable technologies enhance the accuracy of health monitoring, but ensuring at the same time user comfort remains a significant challenge. Flexible strain sensors have emerged as promising candidates for this task, thanks to their ability to conform to the body and capture subtle biomechanical signals. Among these, sensors based on fiber Bragg gratings (FBGs) offer advantages such as high sensitivity, flexibility, compactness, multiplexing capabilities, and immunity to electromagnetic interference. However, most FBG-based flexible sensors require external adhesives or fixations to maintain contact with the skin, which can limit comfort, usability, and reliability of collected data. This study introduces an innovative bilayer wearable (BW) sensor that integrates a single FBG within a stretchable silicone structure combined with a self-adhesive silicone layer. The device can be directly attached to the skin without any additional support, ensuring stable and comfortable wear even during motion. This work details the fabrication process and metrological characterization of the BW sensor exhibiting repeatable behavior under strain and low hysteresis across a wide range of traction speeds. Preliminary tests on healthy volunteers confirmed the sensor’s capability to be applied in biomedical scenarios ranging from vital signs monitoring to biomechanics. In particular, BW was able to accurately detect respiratory and heart rates, as well as joint movement and muscle contraction. The combination of soft adhesion and optical sensing performance makes the proposed BW sensor a promising tool for real-time, reliable health monitoring.