Synergy-induced tunable electromagnetic response and enhanced shielding efficiency in carbon black- and carbonyl iron-reinforced polydimethylsiloxane composites

This work reports the broadband (10 MHz-1 GHz) electromagnetic response and Electromagnetic Interference (EMI) shielding of PDMS- based meta-composites of conducting carbon black (CB) and magnetic carbonyl iron (CI). The prominent inductive character resulting from the three-dimensionally extending conducting network results a transition to negative permittivity in the composites and its frequency can be tuned with the content of CI. Moreover, the combined effect of magnetic resonance in CI as well as the formation of current loops inside the conducting network results a negative permeability in the composites. The Electromagnetic interference (EMI) shielding effectiveness (SET) of the composite is found to progressively improve with CI addition; SET> 60 dB (99.9999%) is obtained for PDMS-CCI@80. A detailed investigation on the absorption as well as the reflection coefficient indicates that the increase in the EMI SE in the composite is strictly based on the dominating microwave absorption mechanisms. Out of the 64 dB obtained for 3 mm thick PDMS-CCI@80, 59.4 dB is due to absorption and 4.6 dB corresponds to the reflection of electromagnetic radiation.