A Tunable Transparent Graphene Absorber with Multifrequency Resonance

The demand for multinarrowband absorber has attracted increasing interest among researchers in recent years. However, integrating multifrequency absorption, tunability, and high optical transparency into an absorber remains a crucial challenge. In this study, a multiband, tunable, and transparent microwave meta-absorber is theoretically proposed and experimentally demonstrated. This meta-absorber is composed of resonant patterns made from graphene and indium tin oxide (ITO), placed on a substrate of lithium niobate (LN). By introducing P-type doping to reduce the resistance of monolayer graphene to around 300 Ω, the impedance matching of the absorber is promoted, consequently manifesting ten absorption points within 40 GHz. The electric field distribution analysis and an equivalent circuit model are employed to elucidate the physical mechanisms of the multiband absorber. Additionally, the lithium niobate dielectric layer possesses a substantial dielectric constant and exhibits phase transition characteristics with temperature changes. When the temperature increases to 250 °C, a comprehensive tuning range of more than 5.49 GHz within 40 GHz range is realized. The maximum tuning range for a single frequency point is 1.33 GHz. With the broadening of the band, the meta-absorber can provide multiple tunable ranges, making it more favorable for practical applications in optical modulator and sensor.