Fig. 2. Flexible fiber optic BCG sensor design and the extraction of hand-crafted fiducial features.

a Exploded schematic illustration of the constituent layers: a bare multimode optical fiber core, a grid-shape nylon deformer, two polyethylene terephthalate (PET) plastic films as core cover, two silicon elastomers encapsulation layers, and a fitting polyester outer covering. b schematic of the microbend fiber sensor. c Sensor output as a function of weight. d Sensor sensitivity as a function of weight. e Illustration of fiducial points labeling. f Sample illustration of five types of fiducial features: extremum—A(J), displacement—∣A(J) − A(K)∣, time interval—T(H, L), time ratio—T₁/T, and area under the curve—AUC(J, K). The periodic contraction (systole) and relaxation (diastole) of the heart can be illustrated into five major stages: (1) atrial systole (AS), (2) isometric ventricular contraction (IC), (3) ventricular ejection (VE), (4) isometric ventricular relaxation (IR), and (5) ventricular filling (VF).