Design And Research Of Tunable Toroidal Dipole Metamaterials

In recent years,with the research of toroidal dipole by scientists at home and abroad,a variety of metamaterials have been designed,so many novel electromagnetic properties of toroidal dipole have also been discovered.Because the metamaterials structure is easier to adjust than natural materials,the metamaterials structure parameters are changed to modulate the electromagnetic properties of the toroidal dipole.This paper studies the electromagnetic characteristics of toroidal dipole by designing a Z-shaped toroidal dipole metasurfaces,including:First,we introduce the related concepts of toroidal dipole,metamaterials,and terahertz waves and the research status at home and abroad.In addition,we also describe the fabrication process and research tools of metamaterial samples in detail,and introduce the equivalent LC circuit of the split ring and the calculation formula proposed by J.Zhou.Since the goal of our research is toroidal dipole,and considering the effects of other multipoles in the multipole family,we also calculated the scattered energy of the multipoles.Secondly,In order to study the modulation effect of metasurfaces structure parameters on the toroidal dipole,we designed the toroidal dipole metasurfaces and changed the Z-shaped metallic longitudinal total length ly,Z-shaped metallic lateral total length lx,Z-shaped metallic width w,length of the short metallic arms e1 and e2 on both sides of the Z-shaped and the distance g between the two incomplete U.We illustrate the existence of toroidal dipole through transmission curves,surface current distributions,and magnetic field distributions,and explain why metasurface structure parameters can produce modulation by establishing LC resonant circuits.The results show that toroidal dipole resonance will be red-shifted when change the metasurfaces structure parameters through the respective transmission curves,but as the Z-shaped metal width w is increased,the toroidaldipole resonance is blue-shifted.We also estimate the resonant frequency at ly=38?m using the established LC resonance calculation formula and the curve function fitted by MATLAB,and proved the both methods can estimate the toroidal dipole resonance frequency within a certain error range.Thirdly,by researching,we found that the metasurface structural parameters and addition graphene could achieve the purpose of tuning.According to this phenomenon,we designed a tunable band-stop filter.In order to illustrate the modulation of the metasurface structure parameters and graphene,we studied the tuning effect of the distance(g)of two incomplete Ushaped spilt rings on the band stop filter,and in order to understand the mechanism of action of g on band stop filter,we constructed the LC resonance model for qualitative analysis.The results show that the band stop filter has a wide stopband and its 3dB stopband is 0.191 THz.Finally,in order to study the modulation effect of graphene on the toroidal dipole,we added a layer of 1 nm thick graphene on the Z-shaped metasurface.We simulated the effect of graphene biasing by changing the conductivity of graphene materials.The results show that the transmittance of the toroidal dipole will change greatly after the addition of graphene on the metasurface,and the Q value and the resonance frequency also have a slight change.