Research On Multi-scale Design And Electromagnetic Absorption Properties Of Electromagnetic Composite Metamaterials

As an artificial materials with special properties,metamaterials can achieve perfect absorption in a certain frequency band,but cannot be compatible with thin thickness and wide frequency band at the same time.Recently,materials with different absorption mechanisms have been widely used in metamaterials.This method can achieve thin thickness and broaden the absorption band.Here,the absorbing properties of composite materials under various loss mechanisms are discussed.The FeSiAl/MWCNT absorbing material was combined with the metamaterial absorber.Through the multi-scale regulation of the absorber,the absorption properties of the metamaterial absorber at different scales are explored.The main contents are as follows:（1）FeSiAl/MWCNT composites were prepared by ball milling,insulation coating,nitric acid passivation and multi-walled carbon nanotubes.The multi-walled carbon nanotubes were added on the surface of FeSiAl to form a particle-carbon nanotube-particle conductive network structure,which can effectively improve the absorption performance of FeSiAl/MWCNT composites.The structure of different FeSiAl/MWCNT composites were characterized by XPS,XRD and FTIR.The surface morphology of the composites was observed by SEM.The electromagnetic properties of the composites were tested by coaxial method.The reflectivity of metamaterial absorbers were tested by bow method.The metamaterial absorbers based on composite material were simulated by CST software,and multi-scale control was carried out.（2）The effects of different milling time on the absorption properties of FeSiAl were systematically studied,and the effects of multi-walled carbon nanotube content on the electromagnetic properties of FeSiAl/MWCNT composites and the improvement of absorption properties were investigated.The EAB of FeSiAl（ball milling for 6 h,thickness of 2.20 mm）reached 3.36 GHz,and the RL_m of FeSiAl（ball milling for 5 h,thickness of 2.45 mm,frequency of 9.44 GHz）reached-52.27 d B.After adding carbon nanotubes,the EAB of FeSiAl/6 wt%MWCNT（ball milling for6 h,thickness of 1.95 mm）reached 3.20 GHz,and the RL_m of FeSiAl/6 wt%MWCNT（ball milling for 6 h,thickness of 2.20 mm,frequency of 8.88 GHz）reached-65.09 d B.（3）TiO₂ shell was coated on the surface of ball milled FeSiAl by coating process,and the effect of multi-walled carbon nanotube content on the electromagnetic properties of FeSiAl/MWCNT composites and the improvement of absorption properties were investigated.The EAB coated with FeSiAl（ball milling for 5 h,thickness of 2.95 mm）reached 3.04 GHz,and the RL_m coated with FeSiAl（ball milling for 4 h,thickness of 5.00 mm,frequency of 4.72 GHz）reached-39.28 d B.After adding carbon nanotubes,the EAB coated with FeSiAl/4 wt%MWCNT（ball milling for 4 h,thickness of 2.70 mm）reached 2.88 GHz,and the RL_m coated with FeSiAl/4 wt%MWCNT（ball milling for 4 h,thickness of 2.70 mm,frequency of 8.24GHz）reached-52.96 d B.（4）The effect of oxidation time on the electromagnetic parameters and absorption properties of FeSiAl was studied by adjusting the time of nitric acid oxidation of FeSiAl,and the effect of MWCNT content on the electromagnetic properties and absorption properties of FeSiAl/MWCNT composites was investigated.The EAB of passivated FeSiAl（ball milling for 6 h,thickness of 2.60 mm）reached2.56 GHz,and the RL_m of passivated FeSiAl（ball milling for 5 h,thickness of 5.00mm,frequency of 4.80 GHz）reached-21.27 d B.After adding carbon nanotubes,the EAB of passivated FeSiAl/8 wt%MWCNT（ball milling for 5 h,thickness of 2.20mm）reached 2.88 GHz,and the RL_m of passivated FeSiAl/8 wt%MWCNT（ball milling for 5 h,thickness of 2.75 mm,frequency of 7.68 GHz）reached-45.81 d B.（5）The influence of multi-scale regulation of metamaterials on absorption properties was studied by using composite materials as matrix.Different metamaterial absorbers were simulated by CST software,and multi-scale control was carried out.The simulation results of the conical metamaterial absorber reached-10 d B in the range of 3-18 GHz,and the absorption peak moved to the low frequency as the absorber became wider and higher.The metamaterial absorber was prepared by using the mold and placed under the bow frame for testing.The results showed that the EAB（-10 d B）of the cylindrical metamaterial absorber was 9 GHz（9-18 GHz）.The trend of the test and simulation results with the frequency was very close,which proved the feasibility of the simulation of the metamaterial absorber.