The main types of magnetic materials that are widely applied in the wireless chargers at present are NdFeB permanent magnets, NiZn ferrite thin disk, MnZn ferrite thin disk, and soft ferrite magnetic stripe.
As the main components of wireless charging technology, a variety of absorbing material disks made of soft magnetic ferrite materials play a role in increasing induced magnetic field and shielding interference of coil. The requirement for performance, size, and reliability of soft magnetic ferrite materials is rather high in a wireless charger. Nevertheless, the receiving end has a higher requirement.
Multi-coil free position type charger can work with multi-terminal at the same time. There are a number of coils arranged in its internal covered most area of the charging dock. Thus, the terminal can be freely placed in the charging dock; the charger will automatically select several efficient transmission coils to work. The working frequency is 105 kHz to 113 kHz for this type of charge according to QI standard regulation. Absorbing material disk uses high Bs and low loss characteristics of MnZn power materials.
According to the way of receiver placement, a wireless charging transmitter is divided into fixed position type, single-coil free position type, and multi-coil free position type. These transmitting terminals have different requirements for ferrite products.
Fixed position type charger applied NdFeB permanent magnet as positioning, terminal equipment must be placed on the fixed position to charge and maximize the charging efficiency. In this charger design, the working frequency is 110 kHz to 205 kHz based on QI standards. The resonance frequency of the fixed position type charger is high, generally using low loss, high-frequency magnetic shielding NiZn ferrite chip as a separate disk.
For single coil free position type charging equipment, there is a drive device in the internal coil which allows plane mobile. By setting the position from the automatic detection device, moving the coil to this position, making the position of the coil in line with the position of terminal receive, eventually realize charging and increase the charging efficiency. With this design, the receiver can be placed at any position on the charging panel. Based on the QI standard, the working frequency is 140 kHz for this charger. Due to the movement requirement of the coil, the absorbing material disk must be high reliability. It needs to use a flexible magnetic disk produced by the taper-casting process.
Permanent magnet materials applied to the wireless charging system, on the one hand, enhance magnetic flux between transmit and receiving coil and improve transmission efficiency; on the other hand, as a positioning device between transmitting and receiving, facilitate fast and exact positioning of the terminal. Small wireless charging equipment mainly uses NdFeB permanent magnet materials; large wireless charging equipment can use ferrite magnets instead of neodymium permanent magnet materials to reduce the cost.
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