Study On High Frequency Electromagnetic Properties Of Ball Milling Carbonyl Iron & FeNi With Orientation And Surface Modification

Nowadays,magnetic materials are widely used in military and civil fields.Several materials such as ferrites,magnetic metal materials,carbon-based composite materials,nanocomposite materials and metal compounds have shown the great potentials in electromagnetic(EM)wave absorption and electromagnetic interference(EMI)shielding fields.In the EM wave absorption field,the stricter requirements for absorbers make the above-mentioned materials still exist some disadvantages,such as large thickness,heavy weight,weak absorbing ability,and narrow absorbing frequency band.What's more,in the field of EMI shielding,people urgently need an EMI shielding material that can not only achieve the good EMI shielding efficiency but also reduce the energy of reflected electromagnetic waves.In this paper,preliminary research on these issues is carried out as follows:1.Based on the impedance matching model and the quarter-wavelength theory,an electromagnetic wave absorbing material with an excellent performance needed to require a higher magnetic permeability together with a matching dielectric constant.In this paper,different types of carbonyl iron soft magnetic materials had been selected and the different ball milling processes had been used to control the morphology of carbonyl iron soft magnetic powder in adjusting its in-plane and out-of-plane anisotropy fields.The soft magnetic composites of carbonyl iron/polyurethane(PU)with easy surface anisotropy were prepared by scraping orientation and hot pressing process,which made the high frequency ability break through the Snoke limit and finally obtained a higher permeability in GHz band and realize the efficient absorption of electromagnetic waves under a thin layer.2.In order to solve the problem that the absorption frequency band of the single-layer absorber was still narrow,Matlab software was used to simulate an ultra-wideband double-layer absorber that could cover the three bands of S,C,and X in many experimental data.The double layer composite was prepared by experiments,and the microwave absorption performance of the double layer composite was further verified by vector network analyzer.3.In order to obtain an excellent EMI shielding material,we prepared the FeNi soft magnetic powder with easy surface anisotropy by high-energy ball milling process.The FeNi/ polyurethane(PU)composite was prepared by scratch-coating orientation and hot-pressing process and the EMI shielding efficiency was measured.A low reflection EMI shielding material,carbonyl iron-FeNi/PU composite,was found from numerous experimental data with the help of genetic algorithm.Then we prepared the double-layer EMI shielding material in our experiments.It was verified that this kind of absorbing EMI shielding material could achieve the electromagnetic shielding efficiency while reducing the energy of reflected secondary electromagnetic waves to the minimum.That is to say,the carbonyl iron-FeNi/PU double-layer material not only achieved an excellent EMI shielding effectiveness but also protected the surrounding environment and people's health.In a certain sense,this kind of double-layer EMI shielding material provided a feasible reference for the future development on EMI shielding materials in industry.