Combined design of dielectric material and layer structure of vanadium nitride/graphene composites for ultra-broadband microwave absorption

Vanadium nitride (VN) has gained much attention for microwave absorption due to its high electrical conductivity and easily tunable microscopic morphologies. However, its microwave dissipation ability is yet to be enhanced. In this work, vanadium nitride with 3D/2D hierarchical microflower structure is successfully fabricated via a rapid microwave hydrothermal method followed by a nitridation process enabled by the in-situ upstream thermal decomposition of melamine. By incorporating with N-doped graphene (N-rGO) in different ratios, the proportion of conduction loss and relaxation polarization loss in VN/N-rGO could be tuned, yielding a minimum reflection loss of - 45.9 dB at 10.4 GHz with 5 wt% filler loading. Further, to achieve optimal ultra-broadband microwave absorption, a rational double-layer absorber is constructed by attaching the N-rGO layer with lower normalized impedance but high dissipation capability under the VN/N-rGO layer with excessively high normalized impedance, delivering a maximum effective absorption bandwidth of 10.3 GHz at a total thickness of 4.9 mm. Impedance matching and power loss density distribution analysis are done to illustrate the working mechanism of the double-layer structure.