Figure 2.

(a) Schematic illustration and photograph of a simple-structured triboelectric energy harvester of the metal-to-insulator type in contact-separation mode. Equivalent circuits of the triboelectric energy harvesting system with an external load when the device is in (b) original, (c) pressed, and (d) released states, and (e) corresponding generated current signals during the single cycle. (f) Linear superposition tests of two triboelectric generators (G1 and G2) connected each other in parallel with same and opposite polarity. Reprinted with permission from [90]. Copyright 2013 Elsevier.