Fig. 5. Capacitive tactile behaviors and mechanisms of e-skin.

(A) Skin-attachable MXene-PpyNW-VSNP-PAM–based e-skin placed on the forearm. Investigation proceeds with a proximity mode followed by a pressing mode via a finger of the other person. Photo credit: Yichen Cai and Jie Shen, KAUST. (B) Schematic illustration shows the capacitance mechanism of a parallel plate capacitor. (C) Relative capacitance change decreases when a finger approaches the e-skin. The inset further demonstrates the continuous changes in capacitance when a finger repeatedly approached upon and removed away from the e-skin sensor. (D) Cyclic tests of capacitance changes from a finger approaching the e-skin cyclically (green, from a distance of approximately 2 cm), touching (pink), and finally moving away from it (white). (E) Relative capacitance changes of the e-skin in response to various pressures. (F) Capacitance changes of the e-skin constructed with two tensile sensors for detection of a tiny pressure (40 Pa) and relatively large pressure (400 Pa). (G) Time retention curve of the change in response to capacitance and force. (H) Tactile durability test of the e-skin sensor under a pressure of 1.0 kPa at a frequency of 0.13 Hz. The current change curves were recorded after each 1000 cycles, and 45 cycles of data were presented in each record.