Ultra-broadband and optically transparent metamaterial-based absorber for electromagnetic absorption/shielding

In this paper, an optically transparent ultra-broadband metamaterial-based microwave absorber using indium tin oxide (ITO) deposited on glasses is proposed. The proposed structure integrates two glasses: the upper one is a glass substrate and the lower one is a glass coated with a hybrid metamaterial structure and a grid mesh ground using ITO film. Owing to the multi-resonances of the metamaterial and the impedance matching of the upper glass, the proposed structure obtains an ultra-broadband absorption covering 4.0–17.0 GHz (a relative bandwidth of 123.8%) with over 90% absorptivity. The structure is compact without air gap and the thickness is ∼0.093 times the upper-cutoff wavelength. The physical mechanism is analyzed using equivalent circuit and surface current distributions. Moreover, a grid mesh ground is first proposed to enhance the visible transparency to 74.69% and ensure a low microwave transmission simultaneously. A prototype is fabricated and measured, and the experiments and simulations are in good agreement. The design yields the advantages of ultra-broadband, high light transmittance, and compact, making it suitable for transparent electromagnetic absorption and shielding devices.