A highly stretchable optical strain sensor monitoring dynamically large strain for deformation-controllable soft actuator

In this paper, we report a highly stretchable optical strain sensor that can be compatible with artificial muscle and wearable human-assistive devices. The optical strain sensor is fabricated by embedding a polymeric optical fiber thermoformed for bi-tortuous structure in silicone elastomer. The strain sensor can detect uniaxial strain using amplitude of output light intensity that increases as curvature of the curved regions becomes enlarged with uniaxial strain. Due to the benefits from curvilinear design of the optical fiber and sensor structure with the elastomeric matrix securing geometric recovery from being elongated, the strain sensor is capable of reliable detection of arbitrary tensile strain in a wide range from 0% to 120%. It possesses fast, reversible, and durable strain-sensing performance with a small hysteresis even under continuative cyclic loadings of large strain. As integrated into a soft rolled-actuator based on acrylic elastomer, we finally demonstrate the strain-sensor performance is enough to monitor dynamic deformation response of the soft actuator.