Tuning Negative Permittivity by Anodization of A 3D Copper Network

Abstract

Negative permittivity is a required physical property of metamaterials which has been widely used in some emerging and unconventional applications, such as cloaking, perfect lens and perfect wave absorption. In addition to periodic meta-structured units, a composite with conductive networks, so-called metacomposite, is equivalent to diluted metals, which also exhibits negative permittivity properties at microwave frequency. The percolative metacomposites have the advantages of isotropic property, flexible preparation methods and low cost in achieving negative permittivity. However, building a percolation network from conductive fillers in an insulating matrix is a complicated process, and the dispersion of fillers is difficult to control. In this study, the percolation network was modulated on the basis of the conductive copper foam by anodization treatment. The conductivity and negative permittivity of the foam varied with the anodization time. As the anodization time increased, the foam changed from a typical Drude metal to a less conductive 3D structure with mitigated negative permittivity. The absolute value of the negative permittivity of Cu-30V-5h sample was two orders of magnitude lower than that of the samples anodised for 30V-3h, 20V-3h and 20V-1h. Therefore, anodization is a facile and effective method to control the conductivity and negative permittivity of copper epoxy metacomposites.