Dielectric Properties And Applications Of Large Birefringence Liquid Rystals In Terahertz Bands

Terahertz waves with the frequency range of 0.1-10 THz are situated between the millimeter wave and infrared bands in the electromagnetic spectrum.Because of unique nature,terahertz waves have broad application prospects in biological detection,communication and public safety systems.There has been a lack of efficient materials for direct control of terahertz waves in nature.The high-performance terahertz tunable functional devices are still in its infancy.Due to liquid crystals have anisotropy and mature industrial technology,its application ranges can be extended from the optical band to the microwave band.However,liquid crystals have the following two major problems in the terahertz band: compared with the visible region,the birefringence of liquid crystal shows a comparatively low in the THz range;there is a lack of transparent electrodes in the THz region.In this paper,we present two high birefringence liquid crystal mixtures that were produced by adding eight large birefringence liquid crystals monomers to commercial liquid crystals.A liquid crystals metamaterial transmissive device was designed and fabricated.At the same time,we compare the transmission characteristics of hybrid liquid crystal and commercial liquid crystal.Finally,the effect of the new transparent electrode PEDOT: PSS on the metamaterial absorber was studied.The main contents of this article are as follows:1.The dielectric properties of eight kinds of large birefringence liquid crystals mixed with commercial liquid crystals are studied.The dielectric properties of commercial liquid crystals(E7 and S200)and new mixed crystals(E7-2 and S200-2)at low frequency terahertz are measured by free space method.The dielectric anisotropy of the nematic S200-2 and E7-2 mixtures is 16.4% and 16.3% higher than that of the commercial S200 and E7,respectively.It shows that eight large birefringence liquid crystals can improve the dielectric anisotropy of commercial liquid crystal in the THz band.2.A double-layer metal loop arrays modulation structure based on metamaterial “metal-dielectric-metal”was designed and fabricated.This structure can be used to control the transmission of terahertz waves.The transmission characteristics of mixture liquid crystal materials and commercial liquid crystal on the device were compared.The results show that the mixture liquid crystal materials better improve the performance of the device.3.The effect of the new transparent electrode PEDOT: PSS film on metamaterial absorber was preliminarily explored.The PEDOT: PSS film was spin-coated on the inner surface of the absorber.Before and after spin coating PEDOT: PSS,the resonance peak of the absorber were measured and comprared.The results show that the resonance frequency variable range of the absorber with spin-coating PEDOT: PSS film becomes narrower.The absorption intensity of the resonance peak becomes larger after the voltage is applied.