Tunable ultra-broadband terahertz metamaterial absorbers based on complementary split ring-shaped graphene

In the design of graphene-based tunable broadband terahertz (THz) metamaterial absorbers (MAs), simplifying the gating structure to control the Fermi energy of graphene is a critical requirement for practical applications. To solve this problem, we numerically demonstrate two kinds of tunable ultra-broadband THz MAs based on complementary split ring-shaped graphene. The first absorber exhibits an ultra-broadband absorption performance with an absorptance of above 90% in the frequency range of 2.06–4.24 THz, with a relative absorption bandwidth of 69.2%. By changing the Fermi energy of graphene from 0 to 0.8 eV through bias voltage, the absorptance can be tuned from 32.8% to 99.9%. The ultra-broadband absorption mechanism is based on the surface plasmon polariton resonances caused by the surface charges of complementary split ring-shaped graphene. In addition, to further expand the absorption bandwidth, we cover another dielectric layer on the first absorber to make the second absorber have an increased relative absorption bandwidth of 108.27%.