MHz Permeability Mechanism Of Fe-Based Soft Magnetic Composites

Soft magnetic materials have the important function of energy storage and conversion in electrical and electronic equipment.With the sustainable development of electrification and information technology,increasing the working frequency to improve the efficiency of power conversion and reduce energy loss has become a consensus.However,none of the available soft magnetic material can fully release the potential of the wide bandgap semiconductors that can work at GHz range.Such as soft magnetic metal with high magnetic energy density can not work over 100 k Hz because of the high energy loss,while ferrites with MHz working frequency can not be used in energy conversion devices because of the low energy density.Soft magnetic composites(SMCs)with high saturation magnetization and low energy loss are recognized as the most promising MHz power soft magnetic materials.In this thesis,the effects of particle size,volume ratio and ring height,and particle aspect ratio on MHz range permeability of Fe-based SMCs were studied.The main research contents are shown as follows:1.The effect of particle size on cut-off frequency and permeability of spherical FeSi SMCs was studied.It is found the cut-off frequency of composites increases to 110 MHz by changing the particle size from 116 μm to 24 μm.By applying a DC field to remove the effect of domain walls,it shows the mechanism of MHz cut-off frequency and permeability of SMCs is determined by coherent rotation modulated by the eddy current effect.Combining with eddy current effect and effective medium theory,it shows weaking the effect of eddy current in magnetic particle is an effective way to increase the cut-off frequency of SMCs.2.The effects of ring height and carbonyl iron volume ratio on cut-off frequency and permeability of spherical carbonyl iron SMCs was studied.It is found the cut-off frequency increases to 730 MHz with same 1 MHz permeability by decrease the height of ring(70 vol%),while the 1 MHz permeability increases and cut-off frequency decreases gradually by increase the volume ratio of ring.The results show that MHz cut-off frequency and permeability mechanism of SMCs is determined by the coherent rotation modulated by eddy current effect.By establishing empirical formula for the relationship of ring height and volume ratio with cut-off frequency,it shows optimizing the height and volume ratio of composites is an effective way to increase the cut-off frequency and permeability of SMCs.3.The effect of particle aspect ratio on the cut-off frequency and permeability of Fe-Si SMCs was studied.By increase aspect ratio,the in-plane saturation field of composites decreases to about 4700 Oe,and the out-of-plane saturation field increases to about 2 T.With spherical particle turn into flake,the cut-off frequency of magnetic rings increases from 8 MHz to 170 MHz,and 1 MHz permeability increases from 52 to81.The results show that high cut-off frequency of flake composites is determined by the eddy current effect,and high permeability comes from the decrease of in-plane magnetic anisotropy.Increase particle aspect ratios is an effective way to improve cutoff frequency and permeability of SMCs.