Highly flexible and stretchable optical strain sensing for human motion detection

Strain sensors with high flexibility and stretchability are essential for quantifying strains generated by human activities, due to the soft and curvilinear surfaces of the body. Here, we report the design and fabrication of a highly flexible and stretchable optical strain sensor that is applicable for detection of human motions. The sensor is based on dye-doped polydimethylsiloxane (PDMS) optical fiber, which enables quantitative detection of tensile strains by absorption changes of the light passing through the dye-doped fiber. Elaborate mechanical and strain tests confirm durability, reliability and long-term stability of the sensor device. The sensor exhibits linear and repeatable response in a large dynamic range up to 100%, far exceed the stretchability of conventional silica fibers (< 1%), and the strain accuracy is below +/- 1% . We show that the sensor can be used to monitor various human activities such as joint motion, speaking and deep breathing in real time.