Terahertz high and near-zero refractive index metamaterials by double layer metal ring microstructure

We demonstrate the extensive improvement of the effective refractive index of designed metamaterials through the coupling effect of double layers in terahertz region. It is interesting that when the substrate thickness is decreased to small enough, the effective near zero refractive index can be realized. Both high refractive index and near zero refractive index at different frequency can be realized with designed structure. After optimizing geometric parameters of double-sided metamaterial, the effective ultrahigh refractive index with the peak value more than 100 can be obtained, and the bandwidth of near zero index can be achieved to about 2.0 THz. In order to verify the accuracy of our design, a single layer metallic ring metamaterial was prepared in experiment. The transmission was measured by using terahertz time domain spectroscopy at the frequency range from 0.1 THz to 2.5 THz. It is found that the theoretical design results are basically consistent with the experimental results.