Realization of Bidirectional, Bandwidth-Enhanced Metamaterial Absorber for Microwave Applications.

The ever-increasing interest towards metamaterial absorbers owes to its remarkable features such as ultra-thin nature and design flexibility. Subduing the inherent narrow bandwidth of such absorbers is the prime goal in metamaterial absorber research, as this can widen the applications areas. A greater challenge is to construct bidirectional absorber, which provides direction-insensitive absorption, as most of the existing designs exhibit single sided absorption due to the complete metal film used in the design. This work presents the realization of a bidirectional, bandwidth-enhanced metamaterial absorber with basic elements such as strips and squares optimized to have adjacent resonances leading to a bandwidth-enhanced absorption. The structural evolution of the constituent metallic components towards the formation of bandwidth-enhanced absorption is described. The bidirectional absorber exhibits more than 90% absorption between 13.40 GHz and 14.25 GHz from the two incident directions. The mechanism of absorption is studied with the surface current analysis and the effective parameters of the structure. The choice of the metallic components with four-fold rotation symmetry renders the proposed design to be polarization independent and wide-angle receptive. The numerical studies are verified experimentally at microwave frequencies, which shows a good agreement between them.