Fig. 4: Applications of wireless power transfer.

a Experimental setup for the wireless TENG and wireless power transfer. b A photo of the resonant-coupled transmitter and receiver coils. c A photo of the wirelessly lit up 70 40 mW-rated LEDs with high brightness. d The voltages of the storage capacitors as a function of charging time with the coil distance of 5 cm and 10 cm, respectively at the resonant-coupled and nonresonant-coupled states. The storage capacitor value is 15 µF for both the charging cases. e A photo of a shoe integrated with the MR-WTENG for harvesting walking energy. f The photo of a digital watch that could be wirelessly powered.