Revisiting the "Stick-Slip" Process via Magnetism-Coupled Flexible Sensors with Bioinspired Ridge Architecture.

"Stick-slip" phenomenon that occurs when human fingertip scans across a specific surface is essential to perceive the interactions between skin and the surface. Understanding the "stick-slip" behavior is important for bionic flexible system in applications from advanced robotics to intelligent tactile sensors. However, it is often overlooked owing to the limitations to mimic the soft skin that can tangentially deform/recover with informative electrical feedback. Here, a sandwich-type device with deformable ridge-layer is proposed to analyze the characteristic of stick/slip states in "stick-slip" process. Specifically, it is observed that fast recovery of the sensing architecture is caused by dynamic slip phase that generates periodical signals based on principle of induction. The results experimentally show that periods of the electrical pulses are dependent on factors such as inherent properties (e.g., modulus and geometry) and operational parameters (e.g., scanning speed and normal load), which is consistent with the theoretical model. Furthermore, it is found that the transition between "stick-slip" and full slip could qualitatively reflect interfacial properties such as moisture, roughness, and topology. It is expected that the results can strengthen the understanding of "stick-slip" behavior when fingertip interacts with a surface and provide guidance of flexible sensor design to enrich the biomimetic perceptions.