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An ultra-broadband and optically transparent metamaterial absorber based on multilayer indium-tin-oxide structure

In this work, an ultra-broadband and polarization-insensitive metamaterial absorber (MA) with high optical transparency is presented. Indium-tin-oxide (ITO) films are used as frequency selective surfaces in multiple conductive layers and also as the reflective backplane. Numerical simulation analysis demonstrates that the absorptivity of the proposed absorber exceeds 90% in the frequency range from 10 to 75.5 GHz, corresponding to a relative absorption bandwidth of 153%. The proposed structure has a total thickness of 2.9 mm, which is approximately 1/10 of the free space wavelength of its lowest operating frequency. The absorber also has good polarization insensitivity due to its symmetric geometry. Moreover, for TE-polarized waves, the proposed absorber can maintain an absorptivity greater than 70% for frequencies ranging from 10 to 80 GHz as the incident angle is increased to 45°. For TM-polarized waves, it provides absorptivity of more than 80% at incident angles up to 60°. Surface current distribution on each conductive ITO layer was simulated to analyze the absorption mechanism of the MA. A prototype composed of 16 × 16 unit cells was fabricated and the experimental results show a good agreement with the numerical simulations. Due to its ultra-wideband absorption and wide-incident-angle stability, the proposed MA has potential value in electromagnetic applications such as optically transparent EM shielding and microwave radiation protection.