Abstract
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.
Highlights
Liquid crystals (LCs) feature the fluidity of liquids and the anisotropy of crystals and are considered to be excellent materials for controlling electromagnetic waves
As with the equivalent dielectric constant, the equivalent loss tangent varies with the thickness of the LC layer, but in this study, we mainly focused on dielectric constant
The results show that the initial equivalent dielectric constant (ε ) of the LC layer increases with the increase in the thickness of the dielectric constant (ε⊥⊥) of the LC layer increases with the increase in the thickness of the LC layer, while the saturation equivalent dielectric constant (ε ) of the LC layer remains
Summary
Liquid crystals (LCs) feature the fluidity of liquids and the anisotropy of crystals and are considered to be excellent materials for controlling electromagnetic waves. LC-based microwave and THz devices, such as modulators [6], filters [7], absorbers [8], transduces [9,10], and phase shifters [11], can be adjusted and controlled by changing the electric field or magnetic field. They offer the advantages of low power consumption and low cost [12]
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