Multi-scale design of electromagnetic composite metamaterials for broadband microwave absorption

The microwave absorbing composites embedded with magnetic-dielectric lossy components including spherical carbonyl iron (CI) and multi-wall carbon nanotubes (MWCNT) were fabricated by a two-step molding method. By manipulating the content of CI and MWCNT for adjusting complex permittivity and permeability, the as-prepared composites were used to optimize the electromagnetic composite metamaterials (ECMs) for broadband absorption. The multi-scale ECMs achieved -8 dB absorption in 2-40 GHz and -10 dB absorption within the 30 GHz bandwidth, where the minimum reflectivity of -55 dB was found at 14.8 GHz. It is found that the magnetic and dielectric loss materials are responsible for attenuating the electromagnetic energy, while the structure of the metamaterials are mainly linked with the broadband absorption via impedance match improvement and electromagnetic field manipulation. The results suggest that multi-scale design for ECMs is an attractive avenue to enhance microwave absorption performance via utilizing ternary composites and tailoring geometrical sizes for absorption resonance.