Abstract
As one of the basic component materials of metamaterials, natural negative dielectric constant (permittivity) materials have attracted more and more attentions; however, the frequency-dispersion mechanism of negative permittivity, especially the preferable low-frequency-dispersion behavior, still needs to be further explored. In this work, we fabricated the carbon nanotubes (CNTs)/epoxy composites by mechanical mixing and pressure forming. By gradually controlling the CNT content, a percolation phenomenon occurred and the conductive mechanism was changed from hopping conductivity to metal-like conductivity. The Debye model was used to describe the dielectric relaxation when the CNT content was below the percolation threshold; the negative permittivity comes from the plasma oscillation of free electrons in CNT networks when the CNT content is exceeding the percolation threshold explained by Drude model; the equivalent circuit analysis was used to analyze a capacitive-inductive transition. Most importantly, a low-frequency-dispersion and weakly negative permittivity occurred in the composites when the CNT content was slightly higher than the percolation threshold, a new Debye-Drude model was put forward to explain the novel frequency dispersion phenomenon of negative permittivity. Our work provides a new method to explain the phenomenon of low-frequency dispersion and will facilitate applications of negative permittivity materials.