Preparation And Characterization Of Magnetic Particle/Nano Carbon Koch Fractal Electromagnetic Shielding Composites

With the rapid development of information technology,the sources of the electromagnetic radiation continue to increase,which will affect people’s health,interfere with the normal operation of equipment,and cause information leakage.Therefore,the development and application of electromagnetic radiation protection materials become more important.Traditional metal protective materials have limited applications due to their shortcomings such as high density and poor oxidation resistance;advanced carbon materials,such as carbon fibers,carbon nanotubes,and graphene,have attracted more and more attention due to their light weight,high strength,and good electrical and thermal conductivity,but when used in the field of electromagnetic protection,their protection frequency bands are narrow,and the protection effects need to be further improved.Therefore,the development of new high-performance electromagnetic protection materials is of great significance.In this paper,the patterning of the fractal structure was introduced into the design of the electromagnetic shielding material to prepare the magnetic particle /nano-carbon Koch fractal layered electromagnetic shielding carbon fiber composite material.In the composite material,different areas of Koch fractal patterns were filled with magnetic particles and nanocarbon,respectively,to constitute the electromagnetic wave absorption layer of the composite material,and glass fiber（GF）was used as the wave-transmitting layer,and carbon fiber（CF）was used as the structural support layer.The effects of Koch fractal times,filler types and layered structure on the electromagnetic shielding properties of composite materials were studied.Moreover,the HFSS electromagnetic simulation software was used to simulate the S21 parameters generated by the fiber layer and the fractal layer through the wave port under the frequency of 2 ～ 18 GHz.The experimental results show that nano-carbon materials and magnetic materials played the role of electrical loss and magnetic loss in composite materials,respectively.Combined with the shielding advantages of the composite layered structure,the two synergistically improved the electromagnetic shielding performance of the composite material.The introduction of Koch fractal structure and the adjustment of fractal times had significant effect on the electromagnetic shielding performance of the composite material,and the second fractal sample had better shielding effect in the frequency range of 2 ～ 18 GHz.In the scheme of Fe（CO）5 @ EP and CNT @ EP as the absorption layer,the performance of the second fractal（n = 2）sample reached a shielded peak of 73.8 d B in the 2.36 GHz band,and the cumulative frequency bandwidth with shielding effectiveness exceeding 55 d B was over 14.3 GHz.As the number of fractals increases,the shielding peak shifted to lower frequencies at 1 ～ 6 GHz.And in the scheme of Fe₃O₄ @ EP and 3DC @EP as the absorption layer,as the number of Koch fractals continued to increase,the shielding effect of the composite material in the 6 ～ 14 GHz frequency band continued to increase.For the second fractal（n = 2）sample,when the incident wave frequency was 17 GHz,the maximum electromagnetic shielding effectiveness of 80 d B was obtained,and the cumulative frequency bandwidth with the shielding effectiveness greater than 55 d B was above 12.5 GHz.HFSS simulation calculation results show that the Koch fractal structure can produce multi-frequency and multi-absorption protection effect in the X band of 8 ～ 12 GHz,which is basically consistent with the experimental conclusion.The research results have laid a certain experimental and theoretical basis for the application of electromagnetic protection of carbon fiber composite materials.