Graphene to tune microwave absorption frequencies and enhance absorption properties of carbonyl iron/polyurethane coating

Waterborne polyurethane matrix coatings using the carbonyl iron particles (CIP) and graphene sheets (GNs) as electromagnetic wave absorbing fillers were fabricated. The electromagnetic parameters of CIP and GNs were measured in 2-18 GHz by transmission/reflection technology. The reflection loss (RL) of the coatings was measured by the arch method. The electromagnetic loss mechanisms and the effect of GNs addition on absorption properties and of composites were discussed. And the morphology of fillers and the micrographs of coatings fracture surface were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that, the unique electromagnetic properties of GNs can make up the shortage of CIP, and the synergistic effects of dielectric/magnetic composites can improve the electromagnetic wave attenuation. In addition, the electromagnetic wave absorption properties can be adjusted by simply changing the content of GNs and CIP particles to obtain the broadband microwave absorption coatings with small thickness. When the mass ratio is CIP:PU:GNs = 2.5:1:0.01, reflection loss values exceeding -10 dB can be obtained in the frequency range of 10.9 - 18 GHz with a thickness of 1 mm. The models of equivalent circuit and synergistic effect among CIP/GNs/PU composite coating were built to analyze the improvement mechanisms of absorption properties.