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.