All-dielectric ultra-broadband transparent imidazole ionic liquid-based metamaterial absorber with a frustum-shaped structure

In this study, a frustum-shaped addition was made to a cylindrical absorber unit, utilizing 1-ethyl-3-methylimidazolium dicyanamide ionic liquid (IL) to create a transparent all-dielectric liquid metamaterial absorber (A-D ILMMA). The A-D ILMMA achieved over 90% absorption efficiency across 4.86-50.00 GHz, with a 165% relative absorption bandwidth. It maintained robust performance across various polarization angles and achieved over 77% absorption at incident angles of up to 60°. Owing to the excellent thermal stability of the IL, the A-D ILMMA consistently maintained an absorption rate of over 90% across a temperature range from 25 °C to 100 °C. The high absorption rates were attributed to synergistic impedance matching and electromagnetic energy loss. The experimental results confirmed over 90% absorption in the ultra-broadband range of 7.10 GHz to 40.00 GHz, demonstrating the excellent physicochemical properties of ILs and their potential applications.