Imidazole ionic liquids-based ultra-broadband metamaterial absorbers from cross-architecture design

Abstract

Room temperature ionic liquids (ILs) characterized by high dielectric loss factors and conductivity emerge as promising candidates for liquid-based metamaterial absorbers (LMMAs). In this work, the IL 1-ethyl-3-methyl-imidazolium dicyanamide was employed to construct an IL-based LMMA, leveraging a cross-architecture (C-A) design paradigm. Numerical analyses reveal that the C-A ILMMA achieves an absorption efficiency exceeding 90% within the frequency range of 7.5-57.8 GHz, translating to a relative absorption bandwidth of 153%. Moreover, the symmetrical configuration of the C-A ILMMA ensures its robust performance across a comprehensive range of polarization angles (0° to 90°), thereby underscoring its polarization insensitivity. Even with an increased incident angle of 60°, the C-A ILMMA sustains an absorption rate above 85% within the frequency intervals of 9.0-13.3 GHz and 24.7-60.0 GHz, highlighting its broad incident angle absorption capability. Owing to the superior thermal stability of the IL, the C-A ILMMA consistently maintains an absorption rate of over 90% across a temperature gradient from 20 °C to 100 °C. Mechanistic investigations reveal that the optimal absorption of the C-A ILMMA predominantly stems from dielectric polarization loss and the ionic current induced within the ILs. Subsequent experimental evaluations corroborate that the C-A ILMMA exhibits an absorptivity in excess of 90% over an ultra-broadband frequency spanning 10 to 40 GHz, aligning closely with numerical predictions. This IL-based C-A ILMMA not only augments the absorption bandwidth substantially but also enhances the adaptability of ILMMA in more rigorous environments, attributed to the commendable physicochemical properties of ILs.