Accurate Monitoring of Small Strain for Timbre Recognition via Ductile Fragmentation of Functionalized Graphene Multilayers.

Sensitivity and linearity are two key parameters of flexible strain sensors. Although the introduction of microstructures (e.g., channel crack inspired by the geometry of the spider's slit organ) can effectively improve the sensitivity, the sudden breakage of the conductive path in turn leads to poor linearity. In practical applications, in order to achieve precise detection of subtle strains, high sensitivity and high linearity are required simultaneously. Here, we report a strain sensor design strategy based on the ductile fragmentation of functionalized graphene multilayers (FGMs) in which the conductive path is gradually broken to ensure high sensitivity while greatly improving the linear response of the sensor. The presence of oxygen-containing functional groups plays a key role in the deformation and fracture behaviors of the sensitive layer. High sensitivity (gauge factor ∼ 200) and high linearity (adjusted R-square ∼ 0.99936) have been achieved simultaneously in the strain range of 0-2.5%. In addition, the sensor also shows an ultralow detection limit (ε < 0.001%), an ultrafast response (response time ∼ 50 μs), good stability, and good patterning capability compatible with complex curved surface manufacturing. These outstanding performances allow the FGM-based strain sensors to accurately distinguish the sound amplitude and frequency, highlighting the sensor's potential as smart devices for human voice detection. Such sensors have potential applications in the fields of smart skin, wearable electronics, robotics, and so on.