Double-Layered Microcracks Coupled Strain Sensors with High Sensitivity and Wide Working Range

The flexible strain sensor is a crucial component of wearable technology, offering considerable potential for monitoring physiological signals. Notably, strain sensors based on nanomaterial thin films have gained much attention from researchers due to their excellent performance and ease of preparation. Nevertheless, challenges remain, such as the rapid expansion of cracks in rigid conductive films under strain, which greatly reduces the working range of the sensors. Soft conductive films characterized by small cracks can lead to low sensitivity. This study introduces a novel conductive strategy centered on the double-layered microcracks of gold/PPy (Polypyrrole) composite films. The as-prepared strain sensor exhibits ultrahigh sensitivity with a GF (gauge factor) of ≈3.604 × 10⁷, an expansive working range spanning from 0% to 60%, high strain resolution at 0.02%, and commendable cycling stability. The crack formation and sensing mechanisms are thoroughly investigated, elucidating the key role of the double-layered microcracks in enhancing sensing performance. Ultimately, the practicality of the developed sensors for human health monitoring and human–machine interaction is demonstrated by the accurate detection of vital signs, body motions, weight, and sounds, and the transmission of encrypted messages.