Two-sided topological architecture on monolithic flexible substrate for ultrasensitive strain sensors.

Flexible ultrasensitive strain sensors are highly desirable in view of their widespread applications in wearable electronics, health monitoring systems, and smart robots, where subtle strain detection is required. Yet, traditional fabrication of such sensors was to prepare sensitive layers on the bare or single-sided-structural substrate, leading to limited sensitivity. Herein, a stretchable resistive-type strain sensor was demonstrated by self-assembling conductive networks onto a monolithic polydimethylsiloxane (PDMS) substrate with two-sided topological design, e.g. sinusoid/auxetic binary architecture. The sensitivity of the obtained sensor was greatly improved by 22-fold as compared to the traditional counterpart with a bare substrate. The remarkably good agreement between experimental results and Finite element analysis (FEA) predictions confirmed that the superior sensitivity is a synergistic effect of local strain enhancement derived from the topological structure on the foreside, and an additional strain concentration and reduced Poisson's ratio from the auxetic arrays on the backside. Furthermore, this sensor can withstand an extreme mechanical force (>750 N) because of the shear stiffening characteristic of an auxetic structure. Benefiting from the characteristics of ultrahigh sensitivity (gauge factor ~1744 at 5%), low detection limit (< 0.05%), long-term durability (>500 loading cycles), this as-prepared sensor shows promising in practical applications of high-performance wearable electronics.