Broadband frequency-reconfigurable metamaterial absorber using switchable ground plane

In this study, we propose a broadband frequency-reconfigurable metamaterial absorber using a novel switchable ground plane (SGP). A double resistive square-ring resonator is introduced for broadband absorption. The distance between the top resonator pattern and the ground plane determines the resonant frequency; the proposed SGP is thus capable of switching the absorption frequency band. The SGP can be either ground or reactive, by switching the PIN diodes on and off, respectively. The SGP is placed as the middle layer, between the top pattern and the bottom ground plane. In the low frequency band, the SGP becomes reactive and the bottom ground plane works as the ground plane of the absorber. In the high frequency band, the SGP works as the ground plane and the bottom ground plane does not affect the absorber. The proposed idea is demonstrated via full-wave simulations and measurements. The absorption of the fabricated sample with 27 x 27 unit cells is measured under normal incidence. When the PIN diodes of the SGP are turned on, an absorption higher than 90% is achieved between 3.5-11 GHz. When the PIN diodes of the SGP are turned off, an absorption higher than 90% is achieved between 1.7-5.2 GHz.