Tannin-based carbon foams in microwave frequency range: Toward fully carbon photonic crystal

The electromagnetic (EM) properties of tannin-based rigid carbon foams were investigated in the 26-37 GHz microwave frequency range (Ka-band). It was experimentally proved that 2 mm thick carbon foams of 36-61 mg/cm3 density are almost not transparent to microwave radiation, and this is especially true for the densest foams having the smallest mean cell size. Depending on both cell size and bulk density, the electromagnetic response of carbon foams in the microwave region can be mainly accounted for by either reflection or absorption. In this communication, we demonstrate that the model based on long wave approximation for photonic crystals can be used to describe precisely the obtained experimental EM spectra, and to explain the observed features of the electromagnetic behavior.