Abstract
In this work, MWCNT-ferrite-CIP /silicone composites were fabricated. The electromagnetic shielding and absorption properties were measured by a network analyzer and calculated in 45 MHz ~ 4.5 GHz. The reflection loss was simulated from the obtained complex permeability and permittivity at various sample thicknesses. Electromagnetic shielding effectiveness was improved significantly with increasing MWCNT content over the percolation threshold of about 4 wt% when high electric conductivity resulted from well inter-connection among MWCNTs in the silicone matrix. Less than 5 % electromagnetic wave energy can be transmitted in 45 MHz ~ 4.5 GHz with the addition of 9 wt% MWCNT content. CIP /MWCNT composites generally show better absorption performances (reach 63.61% at 4.5 GHz) than others. With more MWCNTs, the capability of the high absorption is extended to lower frequency range. Ferrite/ MWCNT composites show better absorption performances than that would expect by simple addition. This surplus beneficial effect is proposed to be a result of that the electromagnetic wave got reflected back and forth by the fillers in the material and thus increased the probability of absorption. In some frequency ranges, the absorption of ferrite/ CIP/ MWCNT/ silicone composites is better than both ferrite only and CIP only composite. The reflection loss exceeding -20 dB was observed easily in 0.9 GHz ~ > 4.5 GHz with composite thickness from 3 mm to 10 mm. For 70 wt% CIP/ 5 wt% MWCNT/ silicone composite with 5 mm thickness, the reflection loss reached -91.2dB (99.9999999 %) at 2.28 GH and the bandwidth below -20 dB is 0.96 GHz. In addition, the highest useful frequency bands were observed for ferrite/ MWCNT/ silicone composites and the broadest -20dB bandwidth is observed for ferrite/ CIP/ MWCNT/ silicone composites.