Study On The Design And Mechanism Of Electromagnetic Shielding Material Iron-Nickel Foam

In this paper, we designed open-cell iron-nickel foam, and systematically investigated the microsructure, mechanical properties, electromagnetic shielding effectiveness of the material by using optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), physical properties measurement system (PPMS), coaxial cable method and Focusing lens antenna, and discussed the relations between properties and microstructure.In the thesis, the adventige and disadventiges of metal mesh and permalloy in electromagnetic shielding are summarized and the factors influencing shielding effectiveness are analyzed. Accordingly, open-cell Fe-Ni foam with magnetic material Fe-Ni alloy frame in application in magnetic field and electromagnetic shielding are proposed.The density of open-cell Fe-Ni foam is in the range 0.2g/cm~3～1.2g/cm~3 and the relative density is 2.3%～12%. The open-cell foam is considered stacking by tetrakaidecahedron cell in the space and SEM observations indicate that the metal mass is clustered more toward the nodes along ligaments, and the cross-section of ligament is approximate as circle.Based on the analysis of X-ray fluorescence spectrometry and X-ray diffraction, a similar chemical composition and structure ofγ-(Fe, Ni) is found in open-cell Fe-Ni foam to solid permalloy 1J50 after heat treatment. Moreovere, the Fe and Ni is gradient distributied in the diffusion layer before they are uniform on a ligament.The relations between distribution of elements and magnetic permeability and electrical conductivity are established by integral method. It indicates the maximum magnetic permability is observed for a certain distribution of Fe and Ni before they are uniform distributed in the layer. The analysis of energy diffraction spectrometry indicates that holding time of heat treatment is different with different ligament to reach the maxium magnetic permability.As for the open-cell Fe-Ni foam of 90 ppi (poles per inch) with 3mm in depth and 12% relative density, the shielding effecitivness (SE) is 8dB and 26.5dB in magnetic field and magnetic field of 50Hz, respectively when it is heat treated for 3 hours at 1100℃. Moreover, the grain size ofγ-(Fe, Ni) increases with the holding time of heat treatment, and generally in the range 5μm ~ 30μm. The Magnetic Force Microscopy (MFM) shows that the magnetic domain is banded distribution in grain and there is certain orientation of magnetic domain between different grains.The SE value of open-cell Fe-Ni foam is simulated by Ansoft Maxwell 2D. In this method, the SE value is confirmed to increase with increasing relative density. And the SE is similar to that of solid permalloy when the relative density is 75%. All the results also show that the weight reduce 21.5 percentages when the solid shield with 3mm in depth is substitued by a two-layers shield of solid permalloy with 2mm in depth and foam with 3mm in depth of 81% porosity. Moreover, there is 24 percentages increase in SE value when the distance of two layer is 8mm.Furthermore, the electrical conductivity of open-cell Fe-Ni foams is also calculated by integral method. It shows the electrical conductivity decreses with the increase of temperature and the holding time and hence lead to 2dB ~ 4dB decrease in SE value in frequency range 30kHz~ 1.5GHz. The electrical conductivity also increases with the increasing relative density.The measurement of electromagnetic shielding effectiveness (EMSE) show that the SE value of open-cell Fe-Ni foam is more than 60 dB in the frequency range 30kHz~1.5GHz, and more than 90 dB when the frequency surpasses 26.5GHz. This SE value is similar to that of aluminum in the frequency range 200MHz~400MHz and 2GHz~15GHz, while a little 5dB lower than that of Al in 400MHz~1.5GHz.Compared to traditional materials like copper, iron and steel mesh, it shows better electromagnetic shielding application in wide frenquency band. Study on the mechanism of EMSE indicates he electromagnetic shielding of open-cell Fe-Ni foam is the common effect of reflection and multiple reflections in the whole frequency range investigated, and the SE value can be enhanced by the way either for the increase of electrical conductivity or the surfaces and interfaces of multiple reflections.Compressive stress-strain curve of open-cell Fe-Ni foam include three regions: elastic region, plateau region and densification region. The yield strenghth of open-cell Fe-Ni foam increase with the increasing aspect ratio of ligament...