Design,Preparation And Electromagnetic Characteristics Of Lightweight Graphene-Based Composites

With the continuous development of modern science and technology,electromagnetic wave-related technique have been applied in national defense and civil applications to protect the safety of our people.However,while bringing convenience to people's lives,a series of electromagnetic pollution will inevitably occur.In order to enrich the technology in the military defense field and absorb harmful electromagnetic waves in daily life,the research on microwave absorbing materials is of great significance.Graphene is a typical,electrically lossy,light-weight absorbing material,while carbonyl iron is a typical magnetic lossy ones,and both have good absorption performances.However,the dielectric constant of graphene is relatively large which results in the poor impedance matching.The carbonyl iron has a good absorption effect but the mass is very large.Using it alone does not meet the light-weight requirement of the absorbing material.Barium titanate is a fine,stable,dielectric loss type wave absorbing material,but the unmodified barium titanate has a weaker absorption strength.In this thesis,graphene,carbonyl iron,and barium titanate are used as raw materials to prepare their composite thin-layer microwave absorbing materials.The microwave absorption performance of the combined cast film in the 2-18 GHz band is systematically explored,and the electromagnetic shielding performance of the thin-layer cast film is measured at the same time.It is found that the multilayer absorbing materials constituting the absorption type and the interference type exhibit excellent absorbing properties.The total thickness of the multilayer absorbing material is in the range of 0.45 mm-1.43 mm,and the areal density is in the range of 1.2 kg/m~2-2 kg/m~2.The combined cast film with the maximum reflection loss can reach-43.88 d B,and the-10 d B absorption bandwidth can cover3.88 GHz-11.76 GHz;in the composite thin-layer cast film,the higher the graphene content,the better the shielding effect.The 0.26 mm thick graphene cast film can achieve a shielding performance of-16 d B.On the basis of the above research,graphene,carbonyl iron and lightweight aramid honeycomb with load-bearing structure and filled with absorbent are combined.Introducing the idea of encoding metamaterials,simulations and experiments on three different filling methods of graphene honeycomb structure absorbing materials,the results are consistent,with the change of the structure,the maximum reflection loss moves toward high frequencies,and the-10 d B absorption bandwidth gradually become larger,and the surface density of the material is 0.7kg/m~2,0.69 kg/m~2,and 0.60 kg/m~2 respectively.Finally,this thesis combines single-layer graphene and carbonyl iron honeycomb structure to form a double-layer graphene honeycomb structure absorbing material,and a double-layer graphene and carbonyl iron honeycomb structure,8 mm thick double-layer graphene structure-10d B absorption bandwidth up to 13.75 GHz,5.5 mm thick graphene carbonyl iron double-layer structure-10 d B absorption bandwidth up to 3.48 GHz.The absorbing performance of the 4 mm-thickness graphene carbonyl iron double-layer structure is simulated,and the absorbing bandwidth below-10 d B is up to 3.31 GHz(7.54GHz-10.85 GHz).When electromagnetic waves of different polarization modes are incident,their absorbing performances are all a certain degree of angular stability can be maintained.