Most of the wireless charging technologies we see today use electromagnetic induction technology. We can think of this technology as a separate transformer.

We know that the widely used transformer consists of a magnetic core and two coils (primary coil and secondary coil). When an alternating voltage is applied across the primary coil, an alternating magnetic field is generated in the magnetic core. Thus, an alternating voltage of the same frequency is induced on the secondary coil, and the electrical energy is transmitted from the input circuit to the output circuit.

If the transmitter coil and the receiver coil are placed in two separate devices, when the power is input to the transmitter coil, a magnetic field is generated. When the magnetic field senses the coil at the receiver, a current is generated, so we build a A set of radio energy transmission systems.

The main drawback of this system is that the magnetic field weakens rapidly with the increase of distance. Generally, it can only work in the range of several millimeters to 10 centimeters, plus the energy is diverging in all directions, so the induced current is much smaller than the input current. Energy efficiency is not high. However, there is no problem with objects that come into close contact.

The earliest use of this principle of wireless charging products is electric toothbrushes - electric toothbrushes are often exposed to water, so the use of non-contact charging, can make the charging contact point is not exposed, enhance the water resistance of the product, but also the overall water wash.

There is a coil in the charging socket and the toothbrush. When the toothbrush is placed on the charging stand, there is a magnetic coupling effect. The principle of electromagnetic induction is used to transmit power. After the induced voltage is rectified, the rechargeable battery inside the toothbrush can be charged.

The electromagnetic induction method is characterized by a short transmission distance and a relatively fixed use position, but it has a high energy efficiency and a simple technology, and is suitable for use as a wireless charge technology.