Ultra-broadband Polarization-Independent Wide-Angle THz Absorber Based on Plasmonic Resonances in Semiconductor Square Nut-Shaped Metamaterials

Metamaterials are considered to be a promising candidate of making THz absorber for function devices to replace natural materials. Based on geometry evolution, the electromagnetic characteristics of metamaterials can be tailed to enhance the weak THz response of natural materials. Appropriate constituent selection and inhomogeneous geometry constructions are proved to be effective to extend the narrow frequency band of traditional metal resonator-based metamaterial absorbers. In this work, doped silicon was used as the only constituent, and the inhomogeneous geometry was designed in a very simple way (so-called square nut structure) with the assistant of transmission line theory and geometry evolution methodology. Ultra-broadband absorption from 1.6 to 5 THz was verified numerically with an efficiency over 90 %. Various plasmonic resonance modes including surface plasmon polaritons (SPP) together with local surface plasmonic resonance (LSPR) tuned by the inhomogeneous structures and cavities contributed to this broadband absorption. Further working with this geometrical variation concept, our wheel hub-like structure achieved ultra-broadband absorption from 0.98 to 5 THz. Our investigations could provide an alternative design methodology for the design of metamaterial THz absorbers.