FIG. 3.

(a) Equivalent circuit model of the interface formed between an electrode and the skin. Reproduced with permission from Shad et al., IEEE Sens. J. 20(24), 14565–14577 (2020). Copyright 2020 Authors, licensed under a Creative Commons Attribution (CC BY) license.⁹³ (b) Schematic of the differences in electrode contact on the scalp among wet (left), dry (middle), and semi-dry (right) electrodes, highlighting the electrode–skin interface (ESI) and the electrode electrolyte interface (EEI). Reprinted with permission from Li et al., Sens. Actuators, B 277, 250–260 (2018). Copyright 2018 Elsevier.⁹⁵ (c) Representative images of the different types of skin interface electrodes (wet—left, dry—middle, and semi-dry—right). Left panel reproduced with permission from Leach et al., Front. Neurosci. 14, 586 (2020). Copyright 2020 Authors, licensed under a Creative Commons Attribution (CC BY) license.⁹⁸ Middle panel reproduced with permission from Zhang et al., Nat. Commun. 11(1), 4683 (2020). Copyright 2020 Authors, licensed under a Creative Commons Attribution (CC BY) license.¹¹⁵ Right panel reprinted with permission from Li et al., Sens. Actuators, B 237, 167–178 (2016). Copyright 2016 Elsevier.¹²⁵