Highly porous conducting carbon foams for electromagnetic applications

Five different cellular glasslike carbons prepared from tannin-based foam pyrolysed at 900°C and presenting variable electric conductivities have been evaluated for electromagnetic (EM) interference shielding effectiveness (SE) in K_a-band. Sufficiently large dielectric loss tangent was also observed in radio frequency range from 1MHz to 2GHz. The effect of density on the EM response properties in microwaves has been studied and found to correlate well with the electrical conductivity. In particular, the contribution to EM attenuation of absorption / reflection mechanisms was found to be very dependent on the cellular microstructure and changed from the ratio 2/1 for dilute samples (bulk density 0.042 g/cm³) to 3/8 for compact ones (0.150 g/cm³). The maximal 23 dB SE has been obtained in K_a-band for the samples with the highest densities, indicating that the carbon foam being extremely lightweight and characterized by relatively high electrical conductivity can be used as effective multifunctional EM coating.