Metamaterial absorbers realized in an X-band rectangular waveguide

In this paper, we demonstrate six types of metamaterial absorbers （MMAs） by measuring their absorptivities in an X-band （8 12 GHz） rectangular waveguide. Some of the MMAs have been demonstrated previously by using the free space measurement method, and the others are proposed firstly in this paper. The measured results show that all of the six MMAs exhibit high absorptivities above 98%, which have similar absorbing characteristics to those measured in the free space. The numerically obtained surface current densities for each MMA show that the absorbing mechanism is the same as that under the free space conditions. Such a demonstration method is superior to the conventional free space measurement method due to the small-scale test samples required, the simple measure device, and its low cost. Most importantly, the proposed method opens a way to enable MMAs to be used in microwave applications such as matched terminations.