Physicists have long known that energy can be efficiently transmitted between two objects with the same resonant frequency, and the interaction between objects of different frequencies is more weak. The singer can smash one of the bottles with different water volumes without affecting other bottles. This is also like when we are swinging, just sit on the top and let the sagging legs swing together to give the swings the same power. Wireless charging technology makes use of this principle. Similarly, wireless charging technology also applies the principle of electromagnetic wave induction, and related AC induction technology. At the transmitting and receiving ends, a corresponding coil is used to transmit and receive an AC signal that generates an induced signal for charging. The user only needs to The charging device can be charged on a "flat". This type of charging used to appear on watches and razors, but it was not possible to charge a large-capacity lithium-ion battery at that time. The structure of the wireless charger technology is shown in the figure.