Study On The Microwave Absorption Performance Of Flaky FeSiAl/SiO₂ Composite Coatings

The rapid development of modern electromagnetic wave application technology hasprovided people with convenience as well as hidden dangers.Accordingly,the requirements for the performance of the microwave absorbing coatings have become higher and higher.In this paper,starting from the composition design of the coatings,takes the flaky Fe Si Al(FFSA),the graphene(GN)powders and two kinds of surface modification silicon dioxide(DNS-2 Si O2,RNS-A Si O2)particles as the research objects.Different types of absorber coatings were prepared and their electromagnetic properties were studied.The microscopic appearance and size of FFSA,GN,DNS-2 Si O2 and RNS-A Si O2 are studied by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The electromagnetic parameters are measured by the coaxial test method and analyzed by vector network analyzer(VNA),and the loss mechanism of each absorbent is discussed.The FFSA absorbing coatings are prepared polyurethane(PU)as a matrix,and the effect of absorbent content on the absorbing performance of coatings is discussed.The composition of the best absorbing performance is selected,the FFSA/Si O2 absorbing coatings are prepared to study the effect and mechanism of Si O2 on absorbing properties.The FFSA/GN composite absorbing coatings are prepared by optimizing the composition of the absorbent,and the influence of the composite absorbent on the performance of coatings and related electromagnetic wave loss mechanisms.Based on the above research foundation,in order to broaden the effective absorption frequency range and improve the absorption performance,Si O2 was added to the coatings as wave-transparent agent to prepare FFSA/GN/Si O2 composite coatings,and the wave absorption performance and related electromagnetic wave loss mechanisms are studied.Studies of absorbents show that,FFSA used in this paper has higher permeability and smaller coercive force,belongs to soft magnetic material,which mainly depends on the natural resonance to attenuate the energy of electromagnetic waves.GN has high permittivity,which is a typical dielectric loss type material,mainly dependent on polarization relaxationand conductance loss to attenuate the energy of electromagnetic waves.After surface modification,the hydroxyl groups on the surface of DNS-2 Si O2 are replaced by the inert groups,which is dispersible Si O2.The surface of RNS-A Si O2 is active groups,which is reactive Si O2.At the same time,the electromagnetic parameters of Si O2 are very small,belonging to the wave-transparent material,which can effectively broaden the absorption frequency band and improve the absorbing performance of coatings.Studies of coatings show that,the performance of the FFSA absorbing coatings increase first and then decrease with the increase of content,and the frequency of the absorption peak gradually shifts to the low frequency region.When the mass ratio of FFSA and PU is 0.6:1,the absorption peak is-17.9d B,and the effective absorption bandwidth(RL<-10 d B)is 2.9 GHz.The FFSA/Si O2 coatings are prepared and the improvement of the performance of coatings is attributed to Si O2 powders which can improve the level of impedance matching between the coatings and the atmosphere.Because Si O2 powders can improve the level of impedance matching and provide electromagnetic waves into the channel inside the coating.The study of the performance of FFSA/GN composite absorbing coatings found that,the absorbing performance of the composite coatings is improved with the increase of the content of GN.When the mass ratio of GN/FFSA/PU is 0.5%:0.5:1,the absorption peak reaches-23.7d B and the effective absorption bandwidth reaches 3.1GHz.Exceeding the threshold due to the good electrical conductivity of GN forming a local current results in a large amount of reflection of electromagnetic waves on the surface of the coatings,resulting in reduced performance.After the threshold value is exceeded,the local current due to the good conductivity of GN causes electromagnetic waves to be reflected on the surface of the coatings in a large amount,resulting in performance degradation.The performance of the composite coatings is greatly improved by adding Si O2 to the composite coatings to improve the impedance matching level of impedance matching between the coatings and the atmosphere and provide electromagnetic wave channels.When the mass ratio of FFSA/GN/Si O2/PU composite coatings is0.05:0.5%:0.5:1,the minimum reflection loss value reaches-40.6 d B and the effective absorption bandwidth reaches 3.3 GHz.