Design of a polarization-insensitive wideband tunable metamaterial absorber based on split semi-circle ring resonators

In this paper, a polarization-insensitive wideband tunable metamaterial absorber is designed and fabricated. The equivalent circuit model for the absorber has been proposed to describe its absorption phenomenon. The proposed absorber is constructed by a periodic array of unit, which contains four split semi-circle ring resonators with 90° rotated. The symmetric structure of the unit gives rise to polarization-insensitivity. Furthermore, the field distribution and the circuit model of the absorber are studied to demonstrate its absorption mechanism. Measurement results show that the proposed metamaterial absorber obtains a reflectivity of less than -10 dB covering 2.1-2.5 GHz and 3.1-6.8 GHz with the total thickness of 8.8 mm, and the reflectivity performance covering the spectrum from 3.1 GHz to 6.8 GHz could be adjusted by tuning the bias voltage on the PIN diodes.