Microwave shielding and absorbing properties of single- and multilayered structures based on two-phase filler/epoxy composites

Abstract

The microwave absorbing and shielding properties of epoxy composites with multiphase filler were studied in a wide frequency range of electromagnetic radiation (EMR) (1–67) GHz. The multiphase filler consists of carbon nanotubes (CNTs) and dielectric (titanium dioxide TiO2) or ferromagnetic (carbonyl iron Fe) particles. The content of TiO2 or Fe was fixed and equal to 35 wt% and 30 wt%, respectively, while the CNT content was varied from 1 to 5 wt%. It was found that EMR shielding efficiency SET is sufficiently increased with carbon nanotubes content and thickness of the composite especially for epoxy CMs filled with carbon nanotubes and carbonyl iron. The measured complex permittivity data (and permeability for CNT/Fe/epoxy CMs) were used for simulation of the reflection loss RL for studied composites. The simulated data have shown that more pronounced reflection loss $$\left| {\text{RL}_{\min } } \right|$$ = (30–44) dB is observed for 2–3 wt% CNT content in ternary epoxy CMs (sample thickness is 0.5–0.7 mm). For the higher CNT content (4–5 wt%), especially for CNT/Fe/epoxy CMs, the reflection loss $$\left| {\text{RL}_{\min } } \right|$$ was decreased, i.e., the large contribution in EMR attenuation is provided due to EMR reflection on the first air-composite boundary. It was shown that effective bandwidth of $$\left| {\text{RL}_{\min } } \right|$$ at level 10 dB can achieve (8–12) GHz and its position and $$\left| {\text{RL}_{\min } } \right|$$ value can be manipulated by varying the composition and thickness of the composite sample. The absorbing performance of 4-layered composite structures was modeled using electromagnetic parameters of single-layer absorbers based on the three-phase composites and optimal layers composition and thickness were found.