Research On Graphene/iron And Cobalt Ferrite Composite Absorbers

Absorbing material refers to a kind of material that can convert electromagnetic energy into other forms of energy to absorb or greatly weaken the electromagnetic wave incident on its surface.Absorbing materials can shield electromagnetic interference,and have the advantages of light weight,high temperature resistance,corrosion resistance,and large absorption rate in a wide frequency band.In this paper,the fabrication and testing of graphene composite absorbing materials are mainly studied.The absorbing mechanism,structure,morphology and absorbing performance of materials are analyzed,and the influence of different concentration,fabrication method and other factors on the absorption performance is compared.The work during research and design mainly includes the following aspects:(1)Understand the classification and application of absorbing materials,deeply study and analyze the absorbing mechanism of different types of absorbing materials and the causes of different absorbing mechanisms from the microstructure level,understand the electromagnetic wave transmission mode of multi-layer absorbing materials and master the calculation of reflection loss of single-layer absorbing materials with metal plate as the background.(2)Graphene oxide dispersion was fabricated by Hummers method,and then graphene /cobalt ferrite composite absorbing material was synthesized by hydrothermal method.The structure,morphology and thermal stability of the sample were analyzed.The electromagnetic parameters of the sample were measured by vector network analyzer,and the reflection loss of the material was calculated.The results show that the concentration of graphene oxide dispersion has a great influence on the microwave absorption properties of the final composite.When the concentration of graphene oxide dispersion is 1mg / ml,the reflection loss is the largest at 10.5ghz,which is-16.8d B.Higher or lower than this concentration has a negative impact on the microwave absorption properties.(3)Cobalt ferrite magnetic nanoparticles were fabricated by sol-gel method,and then combined with graphene by hydrothermal method.Finally,graphene / cobalt ferrite composite microwave absorbing materials were obtained.The effects of graphene addition on the morphology,structure and microwave absorbing properties of the samples were analyzed and compared.The results show that the addition of graphene can significantly improve the cobalt ferrite and the absorption performance of the composite sample is greatly increased.At12.4GHz,the maximum reflection loss is-19.4d B,and the absorption bandwidth is up to5.4GHz.Compared with(2)graphene / cobalt ferrite samples fabricated by hydrothermal method,the particle size distribution,crystallinity and microwave absorbing properties of the samples prepared by sol-gel method are relatively good,thus improving the microwave absorbing properties.(4)In this paper,the sol-gel process was innovated and improved.The one-step sol-gel process was used to simplify the fabrication process and greatly improve the fabrication efficiency.The nitrogen doped graphene / iron composite absorbing materials were fabricated by one-step reaction using citric acid as complexing agent and urea as carbon source.The XRD and TEM tests showed that the method could effectively synthesize nitrogen doped graphene /iron composite absorbing materials.The samples had better crystallinity,dispersed magnetic nanoparticles more evenly,and the wave absorption performance was outstanding.At the thickness of 3mm,the maximum absorption was found at 12.5GHz.Peaking-37 d B,bandwidth up to 6.2GHz.Compared with the graphene / cobalt ferrite fabricated by sol-gel method,it can be found that the one-step sol-gel method has greatly improved the fabrication process,and the particle size distribution and the crystallinity of the samples have also been improved significantly.