Wearable sensor based on fiber bragg grating with flexible polymer for squat exercise

Monitoring body movement with bend sensor is an important requirement in areas such as medical, sports and robotics. As an imitation of human motion perception ability, the flexible and stretchable strain sensor is expected to achieve the perception performance of human joint movement. The stretchable strain sensors should be able to deform and closely adhere to any surface to achieve accurate monitoring of the signal. Body posture identification through Fiber Bragg grating sensing medium has been extensively utilized for monitoring various engineering structures due to the rewards such as high sensitivity, the simplicity of application, great consistency, light mass, minor size, flexibility, upright stability, and safe to electromagnetic interference. In this study, we presented a wearable sensor for monitoring knee posture based on FBG and Polydimethylsiloxane as flexible polymer. The PDMS-coated FBG sensor was embedded on commercial knee protection to make easy to wear. The relationship between knee angle and wavelength response was fitted in a working range of 30 to 120° during knee flexion and extension, because the safe angle ranges are 0 to 50° for rehabilitation patients and 70 to 100° for people with healthy knees. A volunteer performed a variety of squat exercise, and then the wearable sensor successfully measured knee angle in real time. The further experiment was carried out with two posture, correct and wrong, during squat exercise. The correct posture was performed with the waist straight, and the wrong posture was performed with the waist bent. Therefore, during squat exercise, the correct posture can be performed with measuring knee angle and waist response feedback.