Wearable System Based on Flexible FBG for Respiratory and Cardiac Monitoring

There is a growing demand for strain sensors that can be embedded into wearables for several potential applications. Among others, respiratory and cardiac rates’ monitoring from chest wall displacements have driven the development of strain sensors based on fiber Bragg gratings (FBGs) coupled with polymers. In this paper, we addressed the fabrication of a flexible sensor based on an FBG encapsulated into Dragon skin 20 silicone rubber. The sensor is intended to be used for developing a wearable system for respiratory and cardiac rates’ monitoring. The sensor’s response to strain, temperature changes, and relative humidity variations has been experimentally assessed. By considering the repetitive strains induced on the chest wall by the phenomena of interest, the hysteresis response has also been analyzed. Then, an elastic band was equipped with the flexible sensor. The feasibility of this wearable system has been preliminarily assessed on healthy volunteers to evaluate its suitability for monitoring respiratory frequency ( $f_{\mathbf {R}}$ ) and heart rate (HR). The interesting results suggest that the proposed system is easy to be worn, non-invasive, stretchy, and seems to be suitable to well-match the chest wall displacements for monitoring $f_{\mathbf {R}}$ and HR. Such findings call for further investigation targeted to evaluate the accuracy of the FBG-based wearable system in monitoring respiratory and cardiac activities and the system usability in both clinical and sports sciences.