Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate

An equivalent-circuit model is used to analyse the improvement of the wave absorbing performance of the lossy frequency selective surface（FSS） absorber by using a magnetic substrate,showing that it is possible to widen the wave absorbing bandwidth.Three pieces of magnetic substrates are prepared.According to the complex permittivity and permeability,the reflectivity of the corresponding absorber is calculated by the finite difference time-domain（FDTD） method,and the bandwidth of the reflectivity below 10 dB is optimized by genetic algorithm.The calculated results indicate that the wave absorbing performance is significantly improved by increasing the complex permeability of the substrate;the reflectivity bandwidth below 10 dB of the single layer FSS absorber can reach 3.6-18 GHz with a thickness of 5 mm,which is wider than that with a dielectric substrate.The density of the FSS absorber is only 0.92 g/cm 3.Additionally,the absorption band can be further widened by inserting a second lossy FSS.Finally,a double layer lossy FSS absorber with a magnetic substrate is fabricated based on the design result.The experimental result is consistent with the design one.

Synthesis of a novel Al foam with a periodic architecture by introducing hollow Al tubes and Al/Mg powders

In this work,we synthesized a brand-new Al foam with a periodic structure via a simple powder metallurgical route.The periodic architecture consists of both hierarchical porous and bi-directional composition-graded structures.The results show that the hierarchical porous material includes large pores on millimeter scale inheriting from the hollow structure of the Al tubes,and small pores on mi-crometer scale produced by the sintering of Al/Mg powders.The bi-directional Mg concentration-graded structure is formed in the tube walls due to the condensation of Mg vapor in the inner tube wall.The addition of Mg powders achieves excellent metallurgical bonding between the Al powders and the hollow tubes at 550℃.The plateau stress and energy absorption capacity of the Al foam in y-axis compression are significantly higher than that in the x-axis due to their anisotropic structure.In general,the Al foam with Mg addition presents the most superior compression performance,and we believe that our find-ings could open up a unique strategy for developing high-performance metallic foams with the periodic architecture involving both hierarchical porous and bi-directional graded structure.

Preparation and microwave absorption property of Ni/Al powder

As a functional composite material,nickel-coated aluminum powder has been widely used in conductive fillers,electromagnetic shielding materials and other fields due to its advantages of low density,high conductivity and low cost.In this paper,nickel-plated aluminum powder was prepared by a sodium hypophosphite system.The effects of different nickel coating amounts(the percentage of nickel-plating quality to nickel-plated aluminum powder quality)on the morphology,phase,compaction resistivity and electromagnetic parameters of nickel-plated aluminum powder coating were studied.The X-Ray Diffraction(XRD)results proved the successful preparation of nickel-coated aluminum powders with different nickel coating amounts.The Scanning Electron Microscope(SEM)images clearly show the coating effect under different nickel coating amounts.By plating nickel on the surface of aluminum powder,the surface characteristics of aluminum powder are changed,so as to adjust its conductivity,resistance,stability and other properties,thus affecting its electromagnetic performance and wave absorption performance.The results show that the comprehensive absorbing performance is excellent when the nickel coating amount is 40%.The reflection loss of the sample with a thickness of 2.0mm is less than-10 dB in the frequency range of 10.17–12.38 GHz.When the frequency is 10.72 GHz,the minimum reflection loss reaches
33:17 dB.