Excitation of Electromagnetically Induced Transparency Effect in Asymmetrical Planar Terahertz Toroidal Dipole Metasurfa
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Excitation of Electromagnetically Induced Transparency Effect in Asymmetrical Planar Terahertz Toroidal Dipole Metasurfaces Song Wang 1 & Shuang Wang 1
1
1
& Xiaoli Zhao & Jianyu Zhu & Quan Li
1,2
& Tai Chen
1
Received: 6 October 2019 / Accepted: 17 November 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
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. Keywords Terahertz . Electromagnetically induced transparency . Metamaterials . Toroidal dipole
1 Introduction Metamaterials are the artificial materials with periodic structures that have special physical properties not found in many natural materials, such as super-imaging, cloaking, negative * Shuang Wang [email protected]
1
School of Electronic Engineering, Tianjin University of Technology and Education, Tianjin 300222, China
2
National-Local Joint Engineering Laboratory of Intelligent Manufacturing Oriented Automobile Die & Mould, Tianjin University of Technology and Education, Tianjin 300222, China
Journal of Infrared, Millimeter, and Terahertz Waves
refraction, metamaterial absorbers, reconfigurable metadevices, and classical analogue of electromagnetically induced transparency (EIT) [1–7]. As the planar 2D structure of metamaterials, the metasurfaces greatly reduce the difficulty of 3D structure processing and can achieve the physical phenomenon effectively through reasonable structural design [8]. Among many metamaterial/metasurface applications, Fano resonance-induced EIT effect has attracted extensive attention of researchers [9–12]. EIT is the quantum interference effect originally observed in coherently driven atomic systems, which can be realized by the interference of two different excitation pathways in a threelevel atomic system and resulting in a transparent window in a wide absorption band [13, 14]. In general, the EIT effect is produced by the coupling between the bright mode and the dark mode, where the bright mode is
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