Low-cost wearable device based D-shaped single mode fiber curvature sensor for vital signs monitoring

A low-cost wearable pulse and respiratory monitoring system based on D-shaped single mode fiber (SMF) curvature sensor is proposed and investigated. The curvature sensing performance of D-shaped SMFs with different transmission loss are tested and analyzed, and the sensitivity up to − 7.208%/m−1. The D-shaped optical fiber structure is encapsulated by polydimethylsiloxane (PDMS) and implanted in a wrist strap, which realizes good wearability and comfort in the process of human pulse monitoring. The system adopts laser source module and signal acquisition module for integrated and miniaturized design, and real time signal acquisition using Field-Programmable Gate Array (FPGA). The real-time monitoring of pulse signal intensity and frequency before and after exercise was realized. The results show that pulse intensity increased after exercise, with a 10%− 30% increase in pulse frequency, which is consistent with the results in medical theory. In addition, the D-shaped SMF encapsulated by PDMS also was implanted into the belt, which also successfully applied to the monitoring of respiratory signals under quiet and walking conditions.