Wearable Wrist Joint Movement Detection Using Two Sensitivity-Enhanced Plastic Optical Fibers

Abstract

We demonstrate two flexible, sensitivity-enhanced plastic optical fiber (PDF) strain sensors embedded in a polyamide wrist brace for human wrist joint movement monitoring. The two sensors are, respectively, featured with a D-shaped side-polished zone of ~40 µm depth and ~30 mm length and etched periodic gratings with a pitch of 3 mm, which correspondingly exhibit around 46.8 and 17.8 times in normalized bending sensitivity by far larger than conventional commercial POF due to more sensitive strain-induced evanescent field interaction with the side-machined fiber. In terms of different detection sensitivity to bending angles, the two modified sensors are separately arranged at the back and side of the wrist and then enable to decouple wrist joint behaviors induced by flexion-extension and abduction-adduction motions. The application therefore shows a great potential for the developed sensors in wearable exercise rehabilitation of human joints.