Electromagneitc Properties Of Single-and Double-layer Microwave Absorbers Based On Y-type Barium Ferrite-based Nanofibers

In recent years,in order to reduce the increasingly serious electromagnetic pollution and interference problems caused by the widespread use of various electronic equipment,and to meet the electromagnetic stealth needs of modern military equipment,the development of new high-performance electromagnetic wave absorption and shielding materials has been highly valued by major countries in the world.Ferrite and carbon-based materials are very important magnetic loss and dielectric loss absorbers in the field of electromagnetic wave absorption,respectively.Ferrite mainly uses its magnetic loss to absorb electromagnetic waves,and has the advantages of strong absorption capacity and wider frequency band;carbon-based materials mainly have the characteristics of low density and strong dielectric loss;in addition,one-dimensional nanomaterials have the advantages of The unique shape anisotropy can provide a different loss mechanism from isotropic particles,which is conducive to dissipating more electromagnetic wave energy and becoming a new type of wave-absorbing material with great development prospects.In this paper,electrospinning technology is used to prepare one-dimensional Co₂Y barium ferrite nanofibers(Co₂Y NFs),and the effect of calcination temperature on its structure and morphology,as well as the relationship between filling amount and microwave absorbing performance are studied;at the same time,the Co₂Y/C composite nanofibers were synthesized by the hydrothermal method,and the microstructure,electromagnetic properties and absorbing properties changed with hydrothermal time were discussed;in addition,a double-layer structure absorber was designed based on the prepared Co₂Y NFs and commercial carbon nanofibers(CNFs),and its structure and performance were adjusted and optimized.The main research results obtained are as follows:1.Preparation of Co₂Y NFs and its microwave absorbing properties.Fired at 1000?for 3 hours can form pure Co₂Y barium ferrite with hexagonal structure,and maintain a good fibrous morphology.The fiber thickness is relatively uniform,and the average diameter is about 300?400 nm.With the increase of the filling amount,the microwave absorbing ability of the Co₂Y NFs single-layer absorbing coating first increases and then decreases.When the coating thickness is 1.9 mm and the filling amount is 65 wt%,the minimum reflection loss is-12.6 d B at 18 GHz,and the effective absorption bandwidth with reflection loss less than-10 d B is 2.6 GHz(15.4?18 GHz).In addition,when the coating thickness varies between 1.2 and 3.0 mm,the effective absorption bandwidth reaches 7.4 GHz and the frequency range is 10.6 to 18 GHz.2.Preparation of Co₂Y/C composite nanofibers and its wave-absorbing properties.With the extension of the hydrothermal time,the amount of carbon on the surface of the Co₂Y fiber gradually increases,and the thickness of the carbon layer increases accordingly,forming a Co₂Y/C composite nanofiber with an obvious core-shell structure,and its absorption strength and effective absorption bandwidth both show a trend of first increasing and then decreasing.The composite material synthesized by the hydrothermal time of 8 h has the best absorption performance.When the matching thickness is 2.5 mm,the minimum reflection loss is-28.0 d B at 15.4 GHz,and the effective absorption bandwidth is 7.1 GHz(10.9?18 GHz);the effective absorption bandwidth under the thickness of 1.3?3.0 mm is up to 9.6 GHz,and the frequency range covers 90%of the X-band and the entire Ku-band.The synergistic effect of the magnetic loss of the Co₂Y NFs core and the dielectric loss of the carbon shell makes the absorption strength and effective absorption bandwidth of the composite nanofibers significantly improved compared with pure Co₂Y NFs.3.The structural design and absorbing performance of the double-layer absorber based on Co₂Y NFs and CNFs.When Co₂Y NFs are used as the absorbing layer and CNFs are used as the matching layer,as the content of CNFs increases,the reflection loss of the double-layer absorbing coating with a total thickness of 2 mm first decreases and then increases,while the effective absorption bandwidth gradually increases.The absorption layer thickness d₁=1.65 mm,the matching layer thickness d₂=0.35 mm,and the double-layer absorbing coating with a CNFs content of 3 wt%achieved a minimum reflection loss of-90.4 d B at 14.5 GHz,and the corresponding effective absorption bandwidth was 9.1 GHz(8.9?18 GHz);d₁=1.55 mm,d₂=0.45 mm,and the double-layer absorbing coating with CNFs content of 7 wt%achieves a maximum effective absorption bandwidth of 10.9 GHz,and the frequency range is 7.1 to 18 GHz,covering approximately25%C band and all X and Ku bands.When CNFs are used as the absorption layer and Co₂Y NFs are used as the matching layer,as the content of CNFs increases,the effective absorption bandwidth gradually increases.For the double-layer absorbing coating with CNFs content of 7 wt%,when d₁=1.10 mm and d₂=0.90 mm,a minimum reflection loss of-115.0 d B at 14.2 GHz is reached,and the corresponding effective absorption bandwidth is 7.2 GHz(10.8?18 GHz);when d₁=1.50 mm and d₂=0.50 mm,a maximum effective absorption bandwidth of 9.7 GHz is obtained,and the frequency range is 8.3?18 GHz,covering 90%of the X band and all Ku bands.Compared with Co₂Y NFs or CNFs single-layer absorbing coatings,the corresponding double-layer absorbing coatings show significantly enhanced absorbing capacity and wider effective absorption bandwidth,which is mainly due to the gap between the absorbing layer and the matching layer Good coupling effect and better impedance matching performance.Moreover,by changing the stacking sequence,thickness combination and CNFs content,the performance of the double-layer absorbing coating can be effectively controlled.