Electromagnetic induction and Magnetic resonance
Wireless charging technology originates from wireless power transmission technology and is mainly divided into two methods: low-power wireless charging and high-power wireless charging. Its basic principles mainly include electromagnetic induction and magnetic resonance.
Low-power wireless charging often adopts the electromagnetic induction type, such as the Qi method for charging mobile phones. The electromagnetic induction wireless charging technology utilizes the principle of electromagnetic induction, that is, the phenomenon of generating an induced electromotive force due to the change of magnetic flux. There is a coil in both the charger and the mobile phone. When the magnetic field of the charger meets the magnetic field in the mobile phone, charging will start under the action of electromagnetic induction. However, this method has a short transmission distance and is easily affected by the placement position.
High-power wireless charging often adopts the resonant type, and most electric vehicle charging adopts this method. Resonant charging is an extended form of wireless charging. In resonant charging, there is one or more resonant circuits between the charging base coil and the device coil. These circuits are composed of capacitors and coils and can be precisely adjusted to adapt to relevant applications. Compared to induction charging, resonant charging has many advantages, such as being able to charge multiple devices at once, not requiring the device to be accurately placed on the charging base, allowing a longer distance between the charging base and the device, and being more efficient.
In addition, there are also radio wave type and electric field coupling type in wireless charging, but these two types are currently less applied. The radio wave type conducts power transmission through configuring a radio wave transmitting device on the power supply side and a radio wave receiving device on the power receiving side in the way of DC voltage output and input, with a relatively fast transmission speed but lower security. The electric field coupling type uses the induced electric field generated by two sets of asymmetric dipoles coupled in the vertical direction to transmit electric energy. It is suitable for short-distance charging, has high conversion efficiency, and the position can be unfixed, but it requires large-volume equipment and has low power.