Ultra-broadband metamaterial absorber based on imidazole ionic liquid via center-symmetric concave-convex design

Abstract

Abstract To meet the demand for ultra-broadband absorption, angular and thermal stability, and polarization insensitivity in electromagnetic wave absorbers, a new metamaterial absorber (MMA) is proposed, which incorporates the ionic liquid (IL) 1-ethyl-3-methylimidazolium dicyanamide as the absorber and features a center-symmetric concave-convex (CSCC) structure. The CSCC structure, designed with precise geometry, is combined with the IL layer, and the synergy between them is shown to enhance impedance matching, leading to multiple absorption mechanisms and improved absorption performance. As a result, an ultra-broadband absorption exceeding 90% is achieved in the frequency range of 4.00–50.00 GHz in simulation, corresponding to a relative absorption bandwidth of 170%. In addition, the CSCC ILMMA is also characterized by thermal stability, polarization insensitivity, and angular stability. Excellent performance is maintained under harsh conditions, including oblique incidence up to 60° and temperatures as high as 100 °C. It is demonstrated by experimental results that, in the normal incidence frequency range of 6.80–40.00 GHz, an absorption rate exceeding 90% is achieved, with a relative absorption bandwidth of up to 152%. The key innovation of the design is attributed to the fact that the CSCC structure is capable of effectively enhancing the impedance matching of the absorber, and the integration with the IL leads to significantly improved absorption performance. This design is considered to hold promising potential for applications in radar stealth, sensing, electromagnetic interference shielding, and optoelectronic devices.