Controlling of pseudo-graphite proportion in amorphous carbon to enhance dipole polarization for microwave absorption

Abstract

Carbon derived from polymers as microwave absorbing materials (MAMs) has been extensively explored owing to amelioration of balance between impedance matching and dielectric loss by strategies of morphology, nano-microstructure and intrinsic structure. Nevertheless, it is difficult to discern contribution between ohmic loss and polarization relaxation on microwave attenuation due to lack of methods to control the electrical conductivity at a certain value with distinct dipole polarization. Herein, pseudo-graphite proportion in amorphous carbon was controlled by the degree of polymerization of the precursor that was determined by the oligomerization reaction rate. The close electrical conductivities of amorphous carbon with an appropriate range of pseudo-graphite proportion provided a guarantee for impedance matching while avoiding the disparate effects of ohmic loss, thus, the synthetic amorphous carbon with a controllable pseudo-graphite proportion can be used to investigate the impact of polarization loss on the dissipation of microwave. The relative lower pseudo-graphite proportion within limits provided abundance of defects, provoking dipole polarization loss to achieve enhancement of microwave attenuation. The synthetic amorphous carbon with an appropriate proportion of pseudo-graphite phase exhibited excellent microwave absorption with an effective absorption bandwidth (EAB) of 6.64 GHz at a thickness of 2.2 mm over the whole Ku band. This work provided an efficient method to research the contribution of dipole polarization on electromagnetic response and found an effective direction to achieve broad bandwidth response at low thickness for carbon MAMs.