TENGs integrated into the soles. (a) Structure of the designed multilayer TENG. (b) Photo of an as-fabricated TENG. (c) Open-circuit voltage output of the as-fabricated TENG. Reproduced with permission from [132
]. Copyright Springer Nature, 2015. The 3D schematic illustration to demonstrate the structure of the TENG. (e) Working principles of the multilayer elastomeric TENG. (f) The photo showing the multilayer elastomeric TENG integrated into the sole. (g) The photo to demonstrate the function of the fitness tracker that is powered by the TENG-based self-charging power system. Reproduced with permission from [171
]. Copyright Wiley-VCH, 2017.