A fiber Bragg grating-based smart wearable belt for monitoring knee joint postures

Smart wearable technology is exceedingly desirable in athletic sports due to being lightweight, flexible to bend, soft and comfortable. It can continuously deliver accurate information and deformation. During knee flexion, the upper knee perimeter increases with the shrinkage of the knee joint flexor, and it can be monitored. In this study, a fiber Bragg grating (FBG) smart belt is fabricated by embedding FBG sensors at the center of a special silica gel (with unique adhering characteristics to fix FBG on the surface of the belt) for sensing knee joint movements. Polyvinyl chloride strips were adhered to the surface of the smart wearable belt for better protection. The smart belt was calibrated in the laboratory by a systematical changing knee posture and used to identify body postures at various static and kinematic postures of a male subject. The FBG-based smart wearable belt presented a consistent wavelength change after each step by angle changes at the knee joint position. The wavelength increment of FBG sensors increases linearly with the increasing of the bend angle of the knee joint in static tests, and the related slope ratio was 0.3 nm/degrees. In a jogging test, the measurement sensitivity achieved by the FBG smart wearable belt was within a range between 0.018/degrees and 0.021 nm/degrees for the male subject at the velocities of 2 and 3 km/h, respectively. The smart wearable belt could be a useful index to characterize a simple design and ease of implementation, and could also applied for knee posture circumferential strain measurements, especially for sports activities and monitoring stroke patients. This FBG smart belt can be fabricated to produce smart sensing fabrics.