Preparation Method And Electromagnetic Erformance Study Of Cnt/nano Fe₃o₄/nano Fe Emi Shielding Composites

Nano EMI shielding composites offer a number of prominent technical advantages that surpass traditional EMI shielding materials, including low density, high specific area, excellent mechanical and electromagnetic performance. These remarkable advantages enable such materials to have immense potential in application. Therefore, Nano EMI shielding composites have currently attracted the interest of researchers throughout the world.In this thesis, EMI shielding performance and electromagnetic performance of CNTs, nano Fe₃O₄ , nano Fe and their multi-layer composites are studied. CNT/epoxy(5%, 7.5%,10%wt), nano Fe₃O₄/epoxy(10%,15%wt) and nano Fe/epoxy(10%,15%wt) are prepared respectively. Radar absorbed performance and EMI shielding performance of the nano-composites in the frequency bands of 3.22-40GHz are measured by far-field Radar Cross Section measurement and coaxial waveguide measurement. A computer program is developed by VC++ to calculate permittivity and permeability of the nano EMI shielding composites and try-layer composites, and the shielding performance is simulated by CST Studio simultaneously.Dispersity and deaeration problems of nano materials mixed in epoxy matrix are studied in the process of preparation. Dispersant CTAB are used to depress the conglobation of CNTs. The mixtures of nano materials and epoxy are dispersed by ultrasonic vibration so that they form homogeneous composites. Epoxy are heated to pull down its mucosity, and three times of vacuum-pumping are conducted to eliminate the air bubble in epoxy before and after adding nano powder. SEM photos demonstrate that the nano powder is homo dispersed in the matrix, and no obvious conglobation exists in the composites.The Radar wave absorbing performance and EMI shielding performance are measured and compared respectively in the process of measurement. The result indicates that the wave absorbing performance of composites relates to the category and content of absorbent. For CNTs wave absorbing materials, the absorbing performance improves while the frequency increases. The max shielding rates entirely approach or exceed 99.9%. The peak values of try-layer ramp-impedance wave absorbing composites consisted of CNTs, nano Fe₃O₄ and nano Fe all achieve 100dB. The shielding performance of try-layer nano-composites is much more prominent in high frequency range. In reference to de-embedding method, formulas are deduced to calculate S parameters of material itself, and a program is developed to compute the dielectric permittivity and magnetic permeability. Shielding mechanism of the nano-composites is thoroughly analyzed by comparing experiment data and simulation curves.