Iron/epoxy random metamaterials with adjustable epsilon-near-zero and epsilon-negative property

Metamaterials with metal conductive phase always suffer from their high negative permittivity (epsilon-negative), the mechanism of negative permittivity is still need to be explored. Herein, we prepared iron (Fe)/epoxy composites by mechanical mixing and pressure forming. With the increase of Fe content, the conductive behavior changed from hopping conduction to metal-like conduction. The permittivity became negative when the iron content exceeded the percolation threshold (0.425), the negative permittivity was caused by the plasma oscillation of delocalized electrons in the iron conductive network. Besides, when the iron content was 50, 55, 60 or 70 vol%, the permittivity changed from negative to positive at certain frequency points, which is called epsilon-near-zero property. We used the Debye-Drude model to analyze this special dielectric behavior, and the fitting results are in good agreement with the experimental results. A transformation from capacitive to inductive was founded by using equivalent circuit analysis model, this suggests that the occurrence of negative permittivity is accompanied by the appearance of inductance and the negative permittivity behavior is inductance. The epsilon-near-zero and epsilon-negative property could be adjusted effectively by simply changing iron content. Our work provides an understanding guidance on the mechanism of epsilon-negative and epsilon-near-zero property and offers an efficient way to regulate the dielectric property.