Flexible Thin-Layer Strain Sensors Made of Natural Rubber

High-performance 2-layer polymeric strain sensors based on natural rubber (NR) and the electrically conductive filler acetylene black (AB) were fabricated. The structure of the sensors and the thickness of the polymer layers were optimized. An optimal sensor design comprised a 2-layered configuration with a nonconductive rubber layer (0.108 mm thick) bound to an AB-containing conductive rubber layer (0.125 mm thick). This configuration had superior mechanical properties with a gauge factor (GF) peaking at 10,607 during the initial stretching cycle and stabilizing at approximately 2800 from the second cycle onward, within a strain range of 54–71%. The sensor maintained high linearity (correlation coefficient = 0.99). It demonstrated outstanding long-term durability, retaining functionality over 5000 dynamic stretching cycles in the 10–50% strain range. Within this strain range, the sensor had a rapid response time of 0.06–0.10 s. A simple fabrication process, combined with high sensitivity, rapid response, and excellent durability underscored its potential for use in human motion detection and other wearable applications.