One-Dimensional And Core-Shell Structure Design Of Electromagnetic Coupling Microwave Absorbers And Application

The rapid development of modern electronic communication technology and the increasing seriousness of electromagnetic pollution have attracted much attention to the research of microwave absorption materials（MAs）.The electromagnetic coupling effect can be used to optimize impedance matching and enhance the characteristics of electromagnetic wave loss and attenuation.Designing absorbers with both dielectric loss and magnetic loss,and integrated structures and functions,becomes a research hotspot in the MAs research area in recent years.Therefore,in this article,according to the“structure determines performance and performance determines application”research route,magnetic Ni nanoparticles and carbon nanofibers（CNFs）are combined by electrospinning and high temperature carbonization technology to construct one-dimensional porous structures.The core-shell structure composites compounded magnetic Fe₃Al and polypyrrole（PPy）by chemical oxidation.The influence of specific microstructure on magnetic loss,dielectric loss and conduction loss was studied,the microscopic mechanism of ferromagnetic resonance,polarization relaxation and microwave attenuation mechanism of absorbers were clarified,and the absorption mechanism and absorption enhancement mechanism were elucidated.In addition,to explore the industrial application prospect of absorbing materials,conductive carbon black（CCB）@Fe₃O₄ absorber was synthesized by sol-gel method,and then CCB@Fe₃O₄/natural rubber（NR）absorbing films were prepared by plasticizing,mixing and vulcanization processes.Thus,three types of absorbing materials with electromagnetic coupling effect were prepared through structural regulation and component design,and their absorption performance and loss mechanism were analyzed.The influence of the dielectric-magnetic loss synergy effect on MAs was investigated and their industrial application was explored.The results are given as follows:（1）The porous Ni/Ni O/CNFs were fabricated by electrospinning combined with vacuum calcination and etching technology using nickel acetate（NiAc）,polyvinyl alcohol（PVA）,silicon dioxide（Si O₂）,sodium hydroxide（Na OH）and deionized water（H₂O）as raw materials.The presence of Ni/Ni O magnetic particles can not only produce magnetic losses but also enhance the dielectric loss of the CNFs.In addition,the porous structure can increase the porosity and specific surface area of the CNFs,prolong the transmission route of EMW,and create conditions for multiple reflection and scattering of EMW.The porous Ni/Ni O/CNFs exhibited the optimal RL of-47.9d B at 9.5 GHz and effective absorption bandwidth of 3.5 GHz（8.1-11.6 GHz）with a matching thickness of 3.0 mm when the vacuum calcination temperature of 650°C.（2）Core-shell Fe₃Al@PPy composites were prepared by chemical oxidative polymerization method using Fe₃Al alloy particles,pyrrole（Py）,ammonium persulfate（APS）,and p-toluene sulfonic acid（p-TSA）as raw materials.The thickness of the PPy shell layer could be adjusted between 0.3 and 1.5μm by changing the addition amount of Py.The EMW absorption performance of the as-prepared samples was significantly enhanced compared with that of pure Fe₃Al,and the optimum RL reached-40.5 d B at 13.3 GHz with an effective absorption bandwidth of 3.28 GHz（11.6-14.88 GHz）,and a matching thickness of 2.0 mm with a core-shell thickness of only 0.8μm when the Py addition amount was 0.75 m L.（3）The CCB@Fe₃O₄/NR absorbing films were prepared by sol-gel method,plasticizing,blending and vulcanizing process using conductive carbon black（CCB）,ferric trichloride（FeCl₃）,ferrous chloride（FeCl₂）and natural rubber（NR）as raw materials,and the EMW absorbing properties of films were controlled by adjusting the addition amount of CCB@Fe₃O₄.The introduction of the CCB@Fe₃O₄ composites greatly ameliorates the interfacial loss and polarization loss of the films,in which the CCB can improve the dielectric constant and conductivity of the materials.The film achieves the optimal RL of-40.5 d B and effective absorption bandwidth of 0.72 GHz（3.28-4.0 GHz）with the matching thickness of 5.0 mm when the CCB@Fe₃O₄ was added at 45 g.