Tunable All-dielectric Metasurfaces Based On Liquid Crystals

Recently,metasurfaces have sparked much interest and become a hot research field.Over the past years,researchers have demonstrated that with metasurfaces,considerable extraordinary properties can be obtained,such as negative refraction index and reversed Doppler effect,which can hardly be found in natural materials.The properties of metasurfaces are closely related to their structure,thus the feasibility of actively tuning the all-dielectric metasurfaces is quite important.Tranditional metallic metasurfaces still suffer from some disadvantages like serious loss,while all-dielectric metasurfaces based on Mie resonances have become a promising method to overcome these disadvantages.It is known that the properties of liquid crystals(LC)such as permittivity and refraction index can be tuned by external electric or magnetic field or temperature.In the past,research on all-dielectric metasurfaces based on LC has focused on the optical frequency band.In this paper,we report on a generic method for magnetically tunable all-dielectric metasurfaces in terahertz and microwave range.The all-dielectric metasurface is imbedded into LC.The external static magnetic field or electric field is employed to adjust ther permittivity tensor of LC,which in turn alters the resonance frequency of all-dielectric metasurface 23 GHz and the tunability is up to 2.7%.The influence of the lattice period and the size of the resonator on the metasurface is also analyzed.Finally,we add a metal plate to the bottom of the metasurface to obtain an adjustable metasurface absorber.The absorption rate can be changed from 99.8%to 62%and the resonant wavelength can be changed from 370.7 microns to 374.4 microns dynamically as external magnetic field is tuned.In microwave range,the all-dielectric resonators are made of ceramic material,calcium titanium dioxide(CaTi03(1wt%Zr02)).Imbed the metasurface into LC.The influence of the resonator on the metasurface is also analyzed.The resonance is obviously shifted 2.1%by tuning external magnetic field.The tunability of this metasurface is confirmed by both simulation and experiment,and the offset of its resonance's frequency in experiment reaches 40 MHz.