Angle-insensitive broadband transparent microwave absorber with high shielding effectiveness

In this work, a specially designed multilayer indium tin oxide (ITO) mesh structure metasurface was proposed as a microwave absorber, achieving both excellent angle-insensitive broadband absorption and high shielding effectiveness (SE). It features gradually changing surface resistance (R ), to expand the absorption bandwidth while maintaining high SE. Also, a folded square ring metasurface was designed to effectively suppress surface wave grating lobes, as well as to reduce the unit size of the metasurface and thus the absorber. What is more, an additional top dielectric layer was used to stabilize the absorption and SE under an oblique incidence condition (≤45°). As a result, an ultra-broadband miniaturized transparent absorber was realized, with an absorption of >80% in a 2.10-14.65 GHz frequency band (150% relative bandwidth) and a SE of >20 dB in 1-12 GHz at normal incident. The relative thickness of the absorber is only ∼0.117λ₀, and the unit size of the metasurface is only 0.083λ₀. The broadband absorption mechanism of the multilayer absorber was analyzed from the aspects of resonance frequency, surface current distribution, and equivalent circuit. In general, the proposed absorber showed angle-insensitive ultra-wideband absorption with high SE at the same time, implying a wide range of applications.