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 the detection of human motions. The sensor is based on dye-doped polydimethylsiloxane optical fiber, which enables the 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 responses in a large dynamic range up to 100%, far exceeding the stretchability of conventional silica fibers (<1%), and the strain precision 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.