A tunable ultra-wideband planar metamaterial absorber

We present a tunable outer square inner circle coupled metamaterial absorber for planar microwave circuits, which is parallel to the electromagnetic wave transmission direction. The tunable ultra-wideband absorption is achieved by loading electrorheological fluid with electrically tunable permittivity in metamaterial absorber. The simulation results show that the absorption of the absorber reaches up to 90% from 31.92 GHz to 81.76 GHz. The absorption band gradually shifts to lower frequency with the increasing of electric field strength applied on electrorheological fluid, which starts from 31.92 GHz and moves to 26.32GHz when electric field strength applied from 0 V/mm to 816 V/mm. Moreover, the upper frequency of the 90% wideband almost no change with the electric field strength.