Strain-ultrasensitive surface wrinkles for visual optical sensors

Wearable tactile sensors have found widespread applications in human health monitoring, motion monitoring, human-machine interactions, and artificial prostheses. Herein, we demonstrate a new and feasible strategy for wearable optical sensors based on surface wrinkles that are ultrasensitive to strain using a bilayer wrinkling system, in which the relevance between strain and the optical signal can be founded on surface wrinkles. The strain (S⃑(ε, θ_S)), the wrinkled topography (W⃑(A, θ_W)), and the reflected optical signal (O⃑(δ, θ_O)) are correlated with each other, allowing simultaneous measurement of the strain magnitude and direction due to the vector property of optical signals. In addition, interactively visualized detection of slight strain has been achieved by a conspicuous structural color change, successfully amplifying the strain signal owing to the ultra-sensitivity of wrinkles and the nonlinearity of the optical signal. The sensor also exhibits electrical safety and immunity to electromagnetic interference and thus may find potential applications in detecting various complex slight strains, such as subtle human motion or object deformation.