Design of an ultra-thin quad-band metamaterial absorber for sensing and antenna performance enhancement

This article presents a polarization-insensitive quad-band microwave metamaterial absorber for sensing and wireless communication applications. This absorber is characterized by a high effective medium ratio (EMR) of 9.76 and provides maximum absorption of 98.49, 95.94, 94.00, and 99.88 % at 3.84, 7.41, 10.56, and 15.66 GHz, respectively. The properties of this absorber have been studied by E-field, surface current, and equivalent circuit model. The absorber is used as a refractive index sensor, giving a maximum sensitivity of Smax = 1.86 GHz/RIU in the Ku-band. A metasurface (MS) consisting of 4 x 4 unit cells of this absorber is employed as a reflector to improve the peak gain of the antenna by 2-5 dB and it shows circular polarization (CP) behavior. In addition, another MS consisting of 1 x 3 unit cells is used as an isolator to reduce the mutual coupling between MIMO elements. Finally, the effect of the metasurface on single and MIMO antennas has been confirmed experimentally.