Tunable Terahertz Transmission Properties of Double-Layered Metal Hole-Loop Arrays Using Nematic Liquid Crystal

Abstract

This article reports on the investigation, manufacture, and testing of a liquid crystal (LC)-based tunable terahertz (THz) metamaterial (MM) metal-dielectric-metal (MDM) structure, which has low insertion loss (IL) and large modulation depth (MD). The demonstrated structure consists of two parallel layers of a quartz dielectric surrounding two copper layers. The copper structures were printed on the inner surfaces of the upper and lower surfaces of the quartz substrate, to form periodic arrays of sub-wavelength circular loops. The transmission characteristics and the LC parameters are calculated and analyzed for THz electromagnetic (EM) waves in the frequency range from 220 to 330 GHz. The experimental results show that at 285.45 GHz, 294.8 GHz, 305.91 GHz, and 314.38 GHz, the IL is below 4.08 dB and an intensity MD greater than 70.56% is available for THz EM waves with normal incidence. By varying the voltage applied to the LC layer (0–4.8 V), which contains the MDM structure, the frequency corresponding to the valley is decreased to 285.45 GHz, with a frequency tunability greater than 13.5%. The theoretical calculations and experimental results are in good agreement. The MDM structure shows good prospects for THz modulators and switches, due to its excellent performance and simple planar geometry.