A tunable graphene-based hyperbolic metamaterial is designed and numerically investigated in the mid-infrared frequencies. Theoretical analysis proves that by adjusting the chemical potential of graphene from 0.2 eV to 0.8 eV, the reflectance can be blue-shifted up to 2.3 µm. Furthermore, by modifying the number of graphene monolayers in the hyperbolic metamaterial stack, we are able to shift the plasmonic resonance up to 3.6 µm. Elliptic and type II hyperbolic dispersions are shown for three considered structures. Importantly, a blue/red-shift and switching of the reflectance are reported at different incident angles in TE/TM modes. The obtained results clearly show that graphene-based hyperbolic metamaterials with reversibly controlled tunability may be used in the next generation of nonlinear tunable and reversibly switchable devices operating in the mid-IR range.

Shortening of switching times of various soft-matter-based tunable metamaterials is one of the key challenges to improve the functionality of modern active devices. Here we show an effective strategy in the evolution of soft-matter-based tunable metamaterials that makes possible acceleration of both on and off switching processes by using a dual-frequency liquid crystal mixture. The frequency-convertible dielectric anisotropy of the dual-frequency mixture enabled us to create a fast-response in-plane switching metasurface at the nanoscale, which could be tuned by an electrical signal with different frequencies. The results clearly show that the resonance of the metamaterial can be continuously and reversibly controlled within a wavelength range of 100 nm as the applied frequency is inverted between 1 kHz and 40 kHz, with a total response time (τ = τON + τOFF) of 1.89 ms. Furthermore, experimental characteristics of the hybrid metamaterial are in great agreement with numerical calculations, which allow us to anticipate active epsilon-near-zero behavior of the metadevice. This work indicates the future development direction of liquid-crystal-based active plasmonic systems.

The terahertz time domain spectroscopy (THz-TDS) system is used to determine the effects of an AC bias voltage on the tunable response of a metamaterial transducer. The tunability of the metamaterial structure, which is based on the rod-split-square resonator, is demonstrated at terahertz frequencies through electrical control of the nematic liquid crystal orientation. Experimental results show that the metamaterial device can be tuned effectively (with transmittance change of up to 19%) by changing the magnitude of the AC bias voltage from 0 to 300 V. This type of tunable metamaterial could find application in the development of devices operating in the THz frequency region for filtering, modulating, and switching of the electromagnetic signals.

We present an electrically tunable metamaterial device consisting of a periodic array of crossed elements embedded in nematic liquid crystal. Our experimental results show that the transmittance and absorption coefficient of the metamaterial device can be substantially tuned (with an absorption coefficient change of up to 22% for 0.82 THz) by switching the liquid crystal alignment, induced by applying an external voltages applied to the wire electrodes. Structured tunable devices may find applications in modulation and switching elements operating in the visible–infrared–terahertz and microwave regimes.

The search for new low loss nematic liquid crystal mixtures with enhanced birefringence and low temperature of nematic-to-isotropic phase transition plays a pivotal role in a development of new applications in the emerging field of thermally tunable metamaterials. Here we maximize thermally induced tunability of a terahertz metamaterial by using a specially designed nematic liquid crystal mixture. It is shown that the resonant response of a metamaterial device can be effectively tuned both in terms of its magnitude and wavelength with the spectral tunability approaching the theoretical limit of 8 GHz. Electromagnetic simulations confirm our tests and match the experimental observations well. The suggested approach opens new routes for next-generation soft-matter-based filtering and sensing components and devices.