Reconfigurable Terahertz Metamaterials

We demonstrate reconfigurable anisotropic metamaterials at terahertz frequencies where artificial “atoms” reorient within unit cells in response to an external stimulus. This is accomplished by fabricating planar arrays of split ring resonators on bimaterial cantilevers designed to bend out of plane in response to a thermal stimulus. We observe a marked tunability of the electric and magnetic response as the split ring resonators reorient within their unit cells. Our results demonstrate that adaptive metamaterials offer significant potential to realize novel electromagnetic functionality ranging from thermal detection to reconfigurable cloaks or absorbers.

Figure 1

(a) Unit cell consisting of a split ring resonator and cantilever legs. (b) Schematic view of a portion of the metamaterial structure highlighting how the SRRs rotate as the cantilever legs bend. (c) and (d) Photographs of portions of two of the THz metamaterial arrays fabricated for this study. The SRRs are $72\mu \mathrm{m}\times 72\mu \mathrm{m}$ with an in-plane periodicity of $100\mu \mathrm{m}$ and an overall dimension of $1\mathrm{cm}\times 1\mathrm{cm}$.

Figure 2

(a) SEM pictures showing the bending of the SRRs following KOH release (first picture) and RTA at 350, 400, and 450 °C. (b) Magnetic Response: Transmission as a function of frequency for various orientations of the SRRs. The black curve is with the SRRs lying in the plane of the substrate, red curve—RTA 350 °C, blue curve—RTA 400 °C, green curve—RTA 450 °C, magenta curve—RTA 500 °C, dashed black curve—RTA 550 °C. (c) Electric Response: color code is same as for (b). (d) Schematic showing the polarization for (b) (on left) and (c) (on right). (e) Bianisotropic response: color code as for (b) and (c). (f) Nonresonant response. (g) Schematic showing the polarization for (e) (on left) and (g) (on right).

Figure 3

(a) Magnetic response: Transmission as a function of frequency for various bending angles (0°—SRR in the plane of the substrate, 90°—perpendicular to the plane of the substrate). Black—0°, red—30°, blue—40°, green—60°, magenta—80°. (b) The extracted permeability with the SRRs at 90°. Black line is the imaginary part of ${\mu }_{zz}$ and the dashed line is the real part. (c) Electric Response: Transmission as a function of frequency for various bending angles. Color code is same as for (a). (d) The extracted electric permittivity with the SRRs at 0°. Black line is the imaginary part of ${ϵ}_{yy}$ and the dashed line is the real part.