CPA induced Hz to THz broadband absorber with switchable perfect absorption between radio-microwave and THz frequency spectrum.

The coherent perfect absorption (CPA) occurring in the graphene sheet suspended in the air can be utilized to develop an ultrathin, ultra-broadband absorber working in the frequency range covering from the few hertz (Hz) to terahertz (THz) with perfect absorption. A graphene sheet is studied for inducing the CPA covering the radio, microwave and lower THz frequency ranges. A graphene resonator able to provide the surface plasmon resonance is combined with the graphene sheet providing CPA at either side of a thin dielectric layer forms metamaterial structure with the cavity and enhances the absorption bandwidth in the THz region by creating a resonance near to the quasi-CPA frequency. A dielectric resonator of silicon working is engraved in the structure which creates the dipolar resonances between the resonances obtained by the formed cavity between the graphene sheet and resonator. This enhances the absorption level in the THz region. The absorption bandwidth is further enhanced to 7 THz by including a graphene disc at the top of silicon resonator. Thus, the multiple multi-order resonances occurring in the silicon dielectric and surface plasmon resonance of graphene resonators are merged with the phenomena of CPA occurring in the graphene sheets to extend the CPA bandwidth in THz regime. The doping level of graphene or its tunable Fermi energy based on the applied DC electric field can provide the tunability in the total obtained absorption bandwidth. The symmetric structure can provide the polarization insensitive behavior with the allowed incident angle of more than 45° with more than 90% absorption.

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