In this work, a new and efficient terahertz reflective phase shifter is proposed. The phase shifter is composed of a metal-dielectric-metal structure with a double dipole patch array, as well as copper grating electrodes immersed within the nematic liquid crystal. More specifically, the employed copper grating electrodes consist of two sets of cross-distributed comb grids, whereas at each set of comb grids can be applied an external bias voltage separately. On top of that, the electric field in the liquid crystal (LC) layer can be continuously changed by enforcing an innovative technique. Consequently, the orientation of the LC molecules was fully controlled by the applied electric field, since the dielectric constant of the LC is controlled by the biased voltage. The phase of the reflective electromagnetic wave can be continuously manipulated. Under this direction, the experimental results show that the phase shift exceeds the value of 180° in the range of 102.5 GHz-104.3 GHz, where the maximum phase shift is 249° at 103 GHz. The proposed work provides a new regulation concept for the implementation of LC-based terahertz devices and the respective applications in the terahertz reconfigurable antennas field.

In this article, we present a study of the equivalent dielectric constant of two nematic liquid crystals (LCs) with different thicknesses, in the region from 90 to 140 GHz. The equivalent dielectric constant of the LCs was measured using a frequency selective surface (FSS). The LC-based tunable FSS with 22 × 25 unit cells was printed on a quartz substrate with an area of 4 × 4 cm2 and a thickness of 480 µm; the LC layer with thicknesses ranging from 30 to 100 µm acted as a substrate. The FSS featured a maximum frequency-shifting range of 8.15 GHz and 30 µm-thick LC layers with mutually orthogonal rubbing directions were deposited on it. The results show that the initial equivalent dielectric constant of the LC layer increased with the LC layer thickness, while the saturation-equivalent dielectric constant remained almost constant. This work provides LC parameters that can be useful for the design of LC-based devices in the millimeter and terahertz ranges.

In this work, we propose a liquid crystal (LC)-based double-dipole phase shifter. By manipulating the electric field, we change the resonant frequency and phase of the electromagnetic wave by deflecting the orientation of LC molecules. We made the LC-based device with a 30 × 30 array of two parallel unequal dipoles on a Quartz substrate. The substrate has an area and thickness of 4 × 4 cm 2 and 480 µm, respectively. The experimental results show that the phase shift of 0 • -385.4 • is achieved at 94 GHz by changing the applied bias voltage on the LC layer from 0 V to 8.4 V. The phase shift is greater than 360 • in the range 91.75-94.85 GHz. When the LC molecules are most significantly affected by the electric field, the maximum precision of phase shift is 4.08 • with a bias voltage of 2 mV.

No abstract

In this paper, we present a novel design of an electrically tunable metamaterial device in the terahertz frequency range of 325–500 GHz. The device is analyzed and optimized using an equivalent circuit and numerical simulation. The experimental and simulation results are almost identical in the entire design frequency range. A maximum modulation depth of 90.87% is achieved in the transmission window. The bandpass width decreases from 102.55 to 28.7 GHz as the bias voltage increases from 0 to 30 V. This structure provides new insights into the potential of electrically tunable terahertz devices for a wide range of applications.