Preparation Of NiZn Ferrite Material And Its Application In 6.78 MHz Wireless Charging Module

Resonant wireless charging technology has become a hot topic in scientific research because it has the advantages of general wireless charging,but also the advantages of long charging distance and the ability to charge multiple objects.Improving the energy transfer efficiency is the key point of wireless charging design,which can be achieved by optimizing the circuit design and model structure,Specifically,improving the coupling between the transmission systems by adding magnetic isolators is more direct and effective.Therefore,it is of great importance to develop high permeability and low-loss magnetic separators that meet the standard of resonant wireless charging.In this thesis,we obtain ferrite that meets the performance requirements by adding Bi₂O₃,Co₂O_3,Y₂O₃ and changing the Ni/Zn ratio.The denseness of ferrite is firstly enhanced by doping with Bi₂O₃,it is shown that Bi₂O₃ promotes grain growth and improves the denseness of the sample.The saturation magnetic induction of ferrite tends to increase with the increase of doping amount,and the growth trend starts to slow down when x≥0.4 wt%.The initial permeability increases with the increase of doping amount,and the permeability decreases when x≥0.7 wt%when Bi₂O₃is doped excessively.One group with Bi₂O₃ doping of 0.5 wt%was selected as the base formulation,and its densities and electromagnetic properties met the performance requirements.Secondly,in this thesis,the effect of ferrite Ni and Zn element content ratio on the performance was investigated on the basis of Bi₂O₃ doping formulation.It is shown that the saturation magnetic induction strength and coercivity of the samples decrease with the increase of Zn²⁺content.And the magnetic permeability tends to increase,while the corresponding cut-off frequency will continue to decrease.When the Zn content x=0.53the sample applied frequency is closest to 6.78 MHz,and the initial permeabilityμ_i=384and quality factor Q=1.8 meet the performance requirements.Based on the above experiments,the effect of Co³⁺on the ferrite properties was also investigated,and it was shown that because of the high magnetic crystal anisotropy of Co³⁺,the cut-off frequency of the material was broadened,the hysteresis loss of the material was reduced and the quality factor Q was increased.The initial permeability of the ferrite is stabilized at 6.78 MHz when the Co³⁺content x=0.03,and the permeabilityμ=373.74 and has a high-quality factor Q=3.8.At the material section,Y³⁺was added to reduce the eddy current loss of the material.The experiments show that Y³⁺refines the grains and increases the resistivity of the material,and the quality factor of the material is greatly improved to meet the performance requirement of low loss,with the quality factor Q=9.23 and AC resistivityρ=8.63×10³Ω·m when the Y₂O₃ doping amount is 0.03 wt%.Finally,according to the performance parameters of Co3+substituted ferrite and Y³⁺doped ferrite,the wireless charging module is constructed and optimized in Maxwell simulation software,and the simulation results of the position parameters on the coil performance are obtained.The transmission efficiency of the wireless charging module is compared with that of the coil without the spacer and with that of the coil without the spacer.