Liu, Mingkai, Mohamad Susli, Dilusha Silva, Gino Putrino, Hemendra Kala, Shuting Fan, Michael Cole et al. "Ultrathin tunable terahertz absorber based on MEMS-driven metamaterial." Microsystems & Nanoengineering 3 (2017): 17033.
The realization of high-performance tunable absorbers for terahertz frequencies is crucial for advancing applications such as single-pixel imaging and spectroscopy. Based on the strong position sensitivity of metamaterials’ electromagnetic response, we combine meta-atoms that support strongly localized modes with suspended flat membranes that can be driven electrostatically. This design maximizes the tunability range for small mechanical displacements of the membranes. We employ a micro-electromechanical system technology and successfully fabricate the devices. Our prototype devices are among the best-performing tunable THz absorbers demonstrated to date, with an ultrathin device thickness (~1/50 of the working wavelength), absorption varying between 60% and 80% in the initial state when the membranes remain suspended, and fast switching speed (~27 μs). The absorption is tuned by an applied voltage, with the most marked results achieved when the structure reaches the snap-down state. In this case, the resonance shifts by 4200% of the linewidth (14% of the initial resonance frequency), and the absolute absorption modulation measured at the initial resonance can reach 65%. The demonstrated approach can be further optimized and extended to benefit numerous applications in THz technology.
.....To quantify the absorption properties of the samples, we measured the reflection spectra with a commercial THz time-domain spectrometer (TeraPulse4000, Teraview Ltd, Cambridge, UK). The incident angle of the THz beam in the spectrometer is 30°, and the polarization is dominated by the TE component........
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