Mechanically Tunable Terahertz Metamaterial Perfect Absorber

Abstract

The development of a wide range of technologies based on terahertz (THz) electromagnetic radiation drives a strong demand for flexible optical elements. Metasurfaces based on metallic resonators offer a versatile toolkit that permits easy tuning over a wide spectral range by the geometric design. Herein, a mechanically tuned metasurface perfect absorber comprised of split‐ring resonators in combination with a metallic mirror in a microcavity arrangement, is demonstrated. By mechanically tuning the length of the microcavity in the range of 10 μm and above, precise control over the perfect absorption condition is exhibited. A maximum recorded extinction of 45.8 dB is obtained at the perfect absorption condition, corresponding to a suppression of the reflected radiation by almost five orders of magnitude. Experiments are performed in a reflection arrangement using a terahertz time‐domain spectrometer. Simulations of the experimental arrangement show that near‐field effects are weak and the enhancement of metamaterial perfect absorption is in agreement with purely interferometric effects.

Terahertz Metamaterial Absorbers

“…In addition, The TMA designed by Piper et al also uses air spacer as the dielectric layer, and the absorption peak can be tuned by adjusting the cavity thickness. [90] The difference from Schalch et al's work is that their precisely tunable experimental system has an accuracy of tens nanometers for tuning the cavity thickness. In addition, it is verified through experiments that the near-field effect has negligible influence on the absorption enhancement, but the interferometric one dominates the TMA response.…”

“…also uses air spacer as the dielectric layer, and the absorption peak can be tuned by adjusting the cavity thickness. [ 90 ] The difference from Schalch et al. 's work is that their precisely tunable experimental system has an accuracy of tens nanometers for tuning the cavity thickness.…”

“…Another type is to apply flexible materials to tunable TMAs, such as polyimide (PI) [89][90][91] and polydimethylsiloxane (PDMS). [93] The electromagnetic response of a TMA is changed by the deformation of flexible material when the continuous and reversible adjustment of the unit cell array is realized by mechanical stretch.…”

“…Reproduced with permission. [ 90 ] Copyright 2021, Wiley‐VCH. c) (Top) Schematic diagram of TMA with and without stretching and (bottom) experimental results of the 1st stretching‐releasing cycle.…”

“…b) (Left) Schematic diagram of TMA with movable top layer and (right) simulated and experimental absorption spectra with different displacements between the two metal layers. Reproduced with permission [90]. Copyright 2021, Wiley-VCH.…”