Preparation And Microwave Absorption Properties Of Graphene/Epoxy Lightweight Absorber

With the rapid development of electronic equipment and communications technology,people increasingly live in a complex electromagnetic environment.Electromagnetic pollution has become a serious concern.Electromagnetic waves not only cause malfunction,but cause leakage of confidential information and adversely affect human health.In the military,with advances in radar technology,some large equipment will confronted with gradually increased threat.How to make these weapons and equipment get effective stealth become a key factor in the modern war.Electromagnetic absorbing materials?RAM?can absorb electromagnetic waves and realize the function of stealth.They will not cause secondary pollution.In the military and civilian they have broad application prospects.In this paper,the epoxy resin matrix composites,with RGO-HGS@Ag,RGO-HGS@Fe₃O₄,RGO-Fe₅₀Ni₅₀ as absorbing agent,were prepared by solution blending.The composites were tested and characterized.On the basis of material research,with RGO-CNTs as absorbing glue,a honeycomb absorbing structure is prepared.With graphene as dielectric layer,copper foil or graphene as reflective layer,a polarization insensitive metamaterial is prepared.The main contents and conclusions of this paper are as follows:?1?The preparation of RGO-HGS@Ag composites,the maximum effective absorption bandwidth?<-10 dB?reached 4.1 GHz,the minimum reflection loss reached-46 dB,the density was 0.7-1.0 g/cm³ between.Good absorbing performance was mainly due to the following aspects:HGS@Ag and its surrounding graphene formed the"core-shell"on the micro structure,special“core-shell”structure and multiple polarization allowed the improvement of RGO-HGS@Ag composite permittivity;Graphene connected originally separated HGS@Ag,thus improving the electrical conductivity of RGO-HGS@Ag composites.Appropriate conductivity increased the dissipation of the incident electromagnetic wave;Graphene and HGS@Ag can offer more reflection interface,when the electromagnetic wave was incident into the composites,the large surface area of HGS@Ag and large aspect ratio of RGO sheets may improve the multiple reflections,allowing the trap of electromagnetic radiation and the increase of propagation path inside the absorber.?2?The HGS@Fe₃O₄ was fabricated via chemical precipitation method.The coercive of HGS@Fe₃O₄ was 58.4 Oe,the saturation magnetization was 49.8 emu/g and the density was approximately 0.37 g/cm³.The the maximum effective absorption bandwidth of prepared RGO-HGS@Fe₃O₄ composite reached 3.6 GHz,the density was 0.57-0.72 g/cm³between.By combining conductive graphene with magnetic Fe₃O₄,the impedance matching condition and attenuation constant were improved,thereby improving the absorbing effect.?3?Surface modified Fe₅₀Ni₅₀ nanoparticles-Reduced graphene oxide epoxy composites with enhanced microwave absorption properties were successfully prepared using a wet chemical method.After surface treatment,the FeNi alloy has lower dielectric constant,which was benifical for impedance matching.FeNi alloy not only serve to improve the magnetic loss and regulate the impedance,but reduce reunion trend of graphene because steric hindrance effect.The maximum effective bandwidth of the composite was 4.3 GHz,the minimum reflection loss reached-23.9dB and the density was between 1.1-1.3 g/cm³.?4?By blending graphene with carbon nanotube,the RGO-CNTs absorbing glue was prepared.Dipping the honeycomb core into the glue would form the honeycomb absorbingstructure.One-dimensionalnanotubeswereincontactwith two-dimensionalgraphene,whichwaseasytoformawell-developed three-dimensional conductive network,improving the dielectric constant and dielectric loss.The cell size,skin thickness,glue type on absorbing effect were studied using numerical simulation.Studies have shown that the loss of the honeycomb structure mainly from the dielectric loss of coatings,electromagnetic waves in the cellular wall of multiple reflections and destructive interference.The absorbing effect was dominated by?/4 wavelength matching theory,multiple reflections theory and interference theory.For 15 mm thick honeycomb structure,the actual test revealed that the effective bandwidth was about 10 GHz?8-18 GHz?.?5?Using graphene film or copper foil as a patch,FR4 or graphene composite as dielectric layer,a cross-shaped polarization insensitive metamaterial absorber was designed.By adjusting the small cross arm length and arm width,the magnetic resonance of the metamaterial occurred.When the arm length and arm width increased,the resonant frequency shifted to lowre frequency.When the sheet resistance of patch layer is small,the increase in sheet resistance has comparatively less effect on absorbing properties.When the square resistance is greater than 0.05?/?,the absorbing properties decreased significantly.The greater the film resistivity,the smaller the induced current and the weaker coupling induced current on surface and bottom surfaces,thus the lower magnetic resonance intensity.When the thickness of substrate layer was much smaller than the operating wavelength,the absorbing mechanism of metamaterial absorber was electromagnetic resonance.When the thickness is odd multiples of 1/4 wavelength,absorbing mechanism was dielectric loss and destructive interference.