Development of an FBG-Based Wearable Sensor for Simultaneous Respiration and Heartbeat Measurement

This work presents a novel fiber Bragg grating (FBG)-based wearable sensor with a high sensitivity to achieve accurate and simultaneous measurement of respiration and heartbeat activities. The proposed sensor prototype consists of an elastic arc-shaped curved structure, a suspended silicone membrane, an optical fiber inscribed with a 3-mm-length FBG sensing element, and a wearable elastic belt. The elastic arched structural component with excellent flexibility directly contacts the chest wall with its arch apex part. Its two ends have been assembled with the tensioned membrane that is prestretched to form a suspended configuration. The FBG optical fiber is wrapped with the silicone membrane to improve the anti-interference ability and overlaps with the geometric chord length direction of the arched structure. With this sensitive arched structure, the loading force along the chest wall’s vertical direction can be amplificated and converted to the horizontal stretching of the suspended membrane, generating tensile strain on the FBG element. This sensor structure offers outstanding merits in terms of high sensitivity, great flexibility, and compactness, making it suitable for wearable device design. The theoretical model that corresponds to the sensing principle has been derived. The finite element method (FEM)-based simulation has been utilized to investigate the sensor’s performances. Experiments for the measurement of respiration and heartbeat activities which are two kinds of highly varied movements in amplitude have been performed to provide precise and clear waveforms and validate the effectiveness of the proposed sensor prototype.