Flexible strain sensor based on embedded three-dimensional annular cracks with high mechanical robustness and high sensitivity

• A strain sensor with high mechanical robustness and high sensitivity. • High sensitivity was realized by embedding 3D cracks to the elastomer. • The formed interpenetrating structure improve the interface performance. Crack-based flexible strain sensor have advantages of high sensitivity and high detection resolution, which have shown high promise for applications in human–machine interface, biological health detection, and electronic skin. However, the conductive layer in the commonly used crack-based strain sensors tends to lift off after repeatedly stressing/releasing because of the weak interface bonding property, limiting the robustness of flexible sensors. Moreover, the cracks induced by the flat membrane structure are concentrated on the two-dimensional (2D) surface, which limits the further improvement of the sensor's sensitivity. In this study, a new type of flexible strain sensor was fabricated by embedding the 3D annular cracks in the elastomer. By optimizing the fiber weaving structure, the maximum gage factor of the device could reach 45 within strain range of 0–15%, and the minimum detection accuracy reached 0.1%. The sensor maintains good linearity within 15% and good hysteresis characteristics within 5%. Besides, the interpenetrating structure formed between the elastomer material and the conductive material resulted in the increase in the stability of the interface, endowing the device with highly stable sensing performance and high mechanical robustness (anti-scratch). Experiments show that the device can be cycled 10,000 times under a strain of 10%. Finally, the proposed sensor was able to detect even small vibrations and human motion characteristics, exhibiting great potential for broad range of practical applications.