Microwave absorption performance of methylimidazolium ionic liquids: towards novel ultra-wideband metamaterial absorbers

Abstract

Here, for the first time, we propose a simple strategy to realize an ultra-wideband metamaterial absorber by using room temperature ionic liquids (ILs) which are a new class of organic salts containing purely anions and cations. At first, the microwave loss characteristics of methylimidazolium ILs were investigated. The results reveal that these ILs have large ionic conductivities and dielectric loss factors which means high conductive loss and dielectric loss of microwaves can both be caused, and the IL with a shorter carbon chain on cation has potential to produce a higher absorption. When the IL [EMIm][N(CN)₂] is properly arranged into periodic cylinders supported by a 3D-printed dielectric bracket, impedance matching can be enhanced in a wide band, and a strong absorption of microwave above 90% can be achieved within the whole frequency range of 8.4–29.0 GHz, which was verified in simulations and experiments. In addition, the IL-based metamaterial absorber can work efficiently at arbitrary polarization angles and wide incident angles from 0° to 45°. Mechanism investigations show that the perfect absorption in ILs-based MMAs is mainly originated from the loss of dielectric polarization and induced ionic currents in ILs. Distinct from metamaterial absorbers based on water or other liquids, such IL-based metamaterial absorber can not only broaden the absorption bandwidth significantly, but also have potential application in a wider temperature range because of the exceedingly high thermal stabilities of ILs.