Excitation of Electromagnetically Induced Transparency Effect in Asymmetrical Planar Terahertz Toroidal Dipole Metasurfaces

We proposed and fabricated J-shaped planar structure metasurfaces to achieve excitation of dual-frequency toroidal dipole resonances simultaneously, which results in electromagnetically induced transparency effect in the terahertz band. The mutual coupling of two asymmetric J-shaped metal rings in the metasurface units excites low-frequency and high-frequency toroidal dipole resonances, and a transparent window was formed. The fitted curves based on the Fano resonance model have a good consistency with the simulated transmission spectrum of the metasurfaces, which explains this coupling effect deeply. The resonant mode and radiant mechanism were revealed by the analysis of the electromagnetic field distribution and the numerical calculation of the multipole moment. Furthermore, the toroidal dipole resonant response can be adjusted by the structural parameter, indicating the sensing characteristics of the metasurfaces. The simple and flexible planar toroidal dipole metasurfaces with electromagnetically induced transparency effect provide more possibilities for the development and application of terahertz functional devices.