Research On MnZn Ferrite Magnetic Sheet And Its Application In The Wireless Charging System

MnZn ferrites can be applied into the 100 kHz ~ 200 kHz Qi standard wireless charging system because of its high saturation magnetic flux density, high permeability, low loss and high resistivity. In the wireless charging receiving module, the apply of MnZn ferrite sheet can improve the power transmission sensing distance and the power transmission efficiency. This paper made the Mn Zn ferrite by oxide ceramic method and presented the impact of the grinding time, additives and the sintering temperature on the microstructure and magnetic properties of Mn Zn ferrite. This paper also made the ferrite sheet by tape-casting method and presented the impact of technological conditions and the sintering temperature on the ferrite sheet. Futhermore, on the wireless charging circuit, this paper studied the difference between two inverter topologies. Finally, the ferrite sheet and the circuit were integrated and the power transmission distance and power efficiency on different ferrite sheets were studied in the last chapter of the paper.The grinding time controls the particle size distribution of the powder, thereby significantly affects and improves the material microstructure and magnetic properties. When the grinding time reaches 2 h, the material obtain a good microstructure and magnetic properties. However, when the grinding time continuely increases, the microstructure and the magnetic properties deteriorate. In this paper, four groups of additives were compared. The results showed 0.05wt%CaO, 0.08 wt%TiO2, 0.03 wt%SnO2, 0.03 wt%V2O5 can give the best microstructure and magnetic properties. Sintering temperature greatly impacts the grain growth of MnZn ferrite. As the sintering temperature increases, the grain size become larger, the grain boundaries get thinner, the porosity decreased. The material microstructure and magnetic properties reach the best point when the sintering temperature reaches 1360 ℃. However, as the sintering temperature continuely goes high, microstructure and magnetic properties deteriorate.Tape casting method significantly affects the appearance and the flexibility of the casting-film. If the film were too thin, the flexibility will deteriorate. And if the drying temperature were too high, the film occurs cracking problem. A uniform, dense, tough film can be made in the condition of thickness 100 μm on the room drying temperature(20oC). The sintering temperature greatly impacts the microstructure and magnetic properties of the ferrite sheet. Low sintering temperature causes little grain growth, and grainsize become overlarge when the sintering temperature is too high. The best microstructure and magnetic properties can be reached when the sintering temperature is 1320℃.Both the single-tube resonant inverter and the half-bridge inverter can be used in wireless charging transmitting terminal. The experiments showed the single-tube resonant inverter is less efficient than the half-bridge inverter which could reach the efficiency of 60%. MCU can communicate transmitting circuit and the receiving circuit effectively. As a MCU, Bq500210 is being apply into the transmitting circuit. The efficiency of different ferrite sheet was tested in the wireless charging system. The results showed the higher the permeability of the ferrite sheet, the higher the inducing distense and the transmitting efficiency can be reached; the thicker the ferrite sheet, the higher the inducing distense and the transmitting efficiency can be reached. When the ferrite sheet is thicker than 0.45 mm, the transmitting efficiency can be more than 50% in the distense of 10 mm.