Tunable multiband terahertz metamaterials using a reconfigurable electric split-ring resonator array

Abstract

We demonstrate micromachined reconfigurable metamaterials working at multiple frequencies simultaneously in the terahertz range. The proposed metamaterial structures can be structurally reconfigured by employing flexible microelectromechanical system-based cantilevers in the resonators, which are designed to deform out of plane under an external stimulus. The proposed metamaterial structures provide not only multiband resonance frequency operation but also polarization-dependent tunability. Three kinds of metamaterials are investigated as electric split-ring resonator (eSRR) arrays with different positions of the split. By moving the position of the split away from the resonator's center, the eSRR exhibits anisotropy, with the dipole resonance splitting into two resonances. The dipole–dipole coupling strength can be continuously adjusted, which enables the electromagnetic response to be tailored by adjusting the direct current (DC) voltage between the released cantilevers and the silicon substrate. The observed tunability of the eSRRs is found to be dependent on the polarization of the incident terahertz wave. This polarization-dependent tunability is demonstrated by both experimental measurements and electromagnetic simulations. Researchers in Singapore have developed metamaterials whose shape and optical properties can be easily reconfigured. Metamaterials are artificial structures much smaller than the wavelength of light that can achieve functionalities not possible with conventional optics. Chengkuo Lee and colleagues at the National University of Singapore achieved reconfigurable control by fabricating metamaterials on micrometer-scale cantilevers. Applying an electrical voltage bends the cantilevers vertically and thus changes the shape of each component in the metamaterial. As the active elements of the device move away from each other with increasing cantilever height, the optical resonance of the device shifts. The researchers performed their investigation in the terahertz regime, although in principle the concept can be applied to the entire electromagnetic spectrum. This approach could lead to novel applications in which optical functionalities can be freely tuned by an electrical voltage.