Abstract: 

Biomimetic flexible tactile sensors endow prosthetics with the ability to manipulate objects, similar to human hands. However, it is still a great challenge to selectively respond to static and sliding friction forces, which is crucial tactile information relevant to the
perception of weight and slippage during grasps. Here, inspired by the structure of fingerprints and the selective response of
Ruffini endings to friction forces, we developed a biomimetic flexible capacitive sensor to selectively detect static and sliding
friction forces. The sensor is designed as a novel plane-parallel capacitor, in which silver nanowire–3D polydimethylsiloxane
(PDMS) electrodes are placed in a spiral configuration and set perpendicular to the substrate. Silver nanowires are uniformly
distributed on the surfaces of 3D polydimethylsiloxane microcolumns, and silicon rubber (Ecoflex®) acts as the dielectric material.
The capacitance of the sensor remains nearly constant under different applied normal forces but increases with the static friction
force and decreases when sliding occurs. Furthermore, aiming at the slippage perception of neuroprosthetics, a custom-designed
signal encoding circuit was designed to transform the capacitance signal into a bionic pulsed signal modulated by the applied
sliding friction force. Test results demonstrate the great potential of the novel biomimetic flexible sensors with directional and
dynamic sensitivity of haptic force for smart neuroprosthetics.

Full Article:https://spj.sciencemag.org/journals/research/2020/8910692/