The Study On The High Frequency Dielectric Properties And Mechanism Of Magnetic Materials

Fe-based nanocrystalline alloys have excellent soft magnetic properties and great potential for applications in the GHz frequency bands.With the rapid development of electronic systems and telecommunication equipment,it is necessary not only to meet the high-frequency working requirements of electronic devices,but also to solve the electromagnetic pollution caused by high-frequency applications.Based on this,higher requirements are proposed for Fe-based nanocrystalline alloys: high permeability and high cut-off frequency.In order to break the Snoek limit,the cut-off frequency and permeability can be improved by regulating the shape anisotropy and using flaky particles.The impedance mismatch caused by permittivity much greater than the permeability will hinder its application.Therefore,understanding the high-frequency dielectric mechanism and solving this problem are critical for high-frequency applications of Fe based nanocrystalline alloys.Aiming at the problem,in this paper,the microwave dielectric spectroscopy of Fe based nanocrystalline alloys with different ball milling time is studied,and the polarization mechanism of the change of dielectric spectroscopy is explained.The dielectric mechanism of high frequency is studied by using dielectric model and effective medium theory.The conclusions show that the dielectric spectroscopy is closely related to the ball-milling time,the permittivity increases with the increasing ball-milling time,the modulus of the complex permittivity |?| increases with the decrease of the relaxation frequency,similar to Snoek formula for permeability and cut-off frequency;combined with classical dielectric model,the dielectric spectroscopy is analyzed,the results show that the Havriliak-Negami equation fits best,which indicates that the dielectric spectrum has relaxation time distribution and asymmetric broadening of relaxation peaks;for the equivalent permittivity of the particles,the order from large to small is flake particles,needle particles and spherical particles,and as the particle aspect ratio becomes smaller or larger,the equivalent permittivity of the composite system tends to nearly unchanged.Subsequently,the effects of conventional annealing and rapid annealing processes on the microwave electromagnetic properties of Fe-based nanocrystalline alloys are studied.The conclusion shows that through the rapid annealing of the material,the permittivity can be greatly reduced,the permeability is basically unchanged,which narrows the gap between permittivity and permeability,through the proof of the improvement of impedance matching,it is found that the wave impedance has achieved an almost perfect match;the holding time of the rapid annealing treatment affects the electromagnetic parameters,the permittivity increases with the increase of the holding time,while the permeability decreases as the holding time increases,it is closely related to the change of grain size;under the 3 mm thickness,the absorption bandwidth of the rapid annealing sample(take-10 d B as the reference point)decreases with the increase of the holding time,and the maximum absorption bandwidth is 2.28 GHz;the sample with 30 s holding time for rapid annealing has the best absorption performance,a maximum reflection loss is-50.07 d B at 2.925 mm thickness,and the absorption bandwidth(take-10 d B as the reference point)increases as the thickness decreases,the maximum absorption bandwidth is 5.78 GHz at 1.5 mm thickness.