Terahertz 3D bulk metamaterials with randomly dispersed split-ring resonators.

While optical systems using terahertz wave are expected to achieve beneficial applications, at present, the materials of the optical elements that compose them must be selected from limited choices. In this study, we propose a three-dimensional bulk metamaterial in which metal microstructures are dispersed in the bulk resin randomly. A bulk metamaterial was designed and fabricated, in which split-ring resonators known as typical metamaterials were dispersed in cyclo-olefin polymer. In the fabrication method, a resin sheet containing split-ring resonators was first prepared and then diced into resin grains containing a single split-ring resonator. Finally, they were filled in a mold and solidified with a resin solution to obtain the target bulk metamaterial. The optical properties of the fabricated bulk metamaterial were measured by terahertz time-domain spectroscopy. The measurement results confirmed that the refractive index deviated from the original refractive index of the cyclo-olefin polymer due to the resonance of split-ring resonators, suggesting that the proposed bulk metamaterials could be used as a new optical material in the terahertz band.