Development of a flexible sensor based on fiber Bragg grating technology for simultaneous respiratory and heartbeat measurements

In the last decades, the growing interest in the use of wearables has fostered the exploitation of innovative technologies in the development of highly performant sensing solutions for monitoring human health. Several sensing elements have been proposed to instrument wearable items and textiles, making them able to detect physiological parameters, including respiratory and cardiac parameters.This work presents a wearable sensor based on fiber Bragg grating (FBG) technology with a novel design to simultaneously measure respiration and heartbeat activities with improvements in optical fiber robustness. The proposed sensor prototype consists of a flexible matrix with an optical fiber inscribed with a 5 mm-length FBG sensing element. Only a small portion of the optical fiber (i.e., 10 mm) is integrated into the polymer matrix. In this way, the FBG is protected by the matrix and can be stretched further without any damage. A metrological characterization of the developed sensor was proposed to better investigate any changes in response to strain and temperature of the encapsulated sensing element compared to a bare FBG. Then, a preliminary assessment of the performance of the flexible sensor in monitoring respiration and heartbeat was carried out on a healthy subject. The flexible sensor was equipped with an elastic band to be fastened around the thorax. The preliminary results of this test foster future investigations to assess the capability of the proposed wearable system in monitoring cardiorespiratory activity considering different measuring sites (e.g., thorax and neck) and under various body positions (e.g., supine and standing).