Multicomponent Composite Layers as Elements for Effective Multilayered Microwave Shields and Absorbers

Constructing a multilayered structure as an absorbing coating is an important tool for improving the characteristics of microwave absorbing (MA) and shielding materials. The influencing factors on microwave absorption performances of multi-layered structures are filler types and loading in composite layers, stacking sequences and thicknesses, etc. Multicomponent epoxy composites with various content (0–5 wt%) of nanocarbon (graphite nanoplatelets (GNP), carbon nanotubes (CNT) and magnetic fillers (30 wt% of Co and Co3O4 particles) were studied in a frequency range (1–67) GHz. The observed enhanced microwave permittivity and dielectric loss tangent in these multicomponent composites is explained by the enhanced contribution of interfacial polarization due to an additional large number of conductive magnetic particles and the formation of more interfaces with accumulated electric charge in heterogeneous structures. The modeling of reflection loss \(RL\) of multilayered composite structures using measured permittivity and permeability spectra showed good microwave absorptive properties. For example, the 4-layered composite structures based on GNP/Co3O4/epoxy layers showed a more pronounced reflection loss \(\left| {RL_{{{\text{min}}}} } \right| \approx 36\;{\text{dB}}\) (sample thickness is 2.5–2.7 mm) and effective bandwidth \(\Delta f_{{10{\text{dB}}}} \approx {24}\;{\text{GHz}}\) compared with single layers. Much better microwave absorption properties of the multi-layered structures compared with the single composite layer can be ascribed to the improved impedance matching with free space and the addition of interior interfaces.