We propose an all-dielectric hollow annular groove ultra-broadband metamaterial absorber
(A-D ILMMA) based on imidazole ionic liquids, which is freed of metallic substrate and
can offer an extremely wide bandwidth of electromagnetic absorption and prominent
wide polarization angle range. When the ionic liquid 1-ethyl-3-methylimidazolium
Tetrafluoroborate ([EMIM][BF4]) with a high conductivity and dielectric loss factor is
arranged into the hollow annular groove unit cells with a 6 mm total thickness, nearly perfect
impedance matching can be achieved in a wide frequency range. Research results show that
the simulated absorptivity is over 90% in 13.9–50 GHz with the relative bandwidth of 113%,
and the corresponding microwave experiment is performed to support the results of the
simulation. Moreover, the A-D ILMMA can work efficiently at arbitrary polarization angles
from 0° to 90° and wide incident angles from 0° to 60°.