Flexible and Stretchable Optical Fiber Strain Sensor based on Nanoparticles and Polymer for Human Motion Detection

Wearable sensors have been developed for various healthcare applications with human motion detection. For strain sensors to be adopted in smart wearable devices for human joint motion detection, it is necessary that they have excellent mechanical properties such as stretchability, flexibility, softness, and they should be non-toxic to the human body. In this paper, we report on a possible candidate for such a sensor: the polymer fiber composited with polydimethylsiloxane (PDMS) and Zinc Oxide (ZnO) nanoparticles. This polymer fiber exhibits softness, flexibility, stretchability, and reproducibility. Moreover, it has a tensile property of over 100% and excellent resilience. The strain evaluation of the ZnO-PDMS polymer fiber with silica fibers on the ends was carried out with a light emitting diode (LED) and photodetector. The strain sensor with polymer fiber has good properties of strain measurement; stable signal recovery, as well as rapid, immediate, and repeatable response in real-time. The polymer strain sensor was evaluated on the human finger and wrist joints for detection of the bending motion. Moreover, because this polymer strain sensor is waterproof, it can be used for measuring finger bending and releasing even in wet conditions. The results demonstrate that the ZnO-PDMS optical fiber strain sensor can be employed in wearable devices for healthcare applications such as sports and rehabilitation.