Inkjet-printed frequency-selective surfaces based on carbon nanotubes for ultra-wideband thin microwave absorbers

A microwave absorber combining frequency-selective surfaces (FSSs) and dielectric layers is presented. FSSs are printed on dielectric layers using a resistive ink made of a suspension of carbon nanotubes. The absorber exhibits a fractional bandwidth of 137%, corresponding to reflectivity lower than $-15$ dB and absorption higher than 90% from 7.30 till 41.95 GHz, meaning a 34 GHz bandwidth, for a thickness of only 0.13 $\lambda$. This performance is obtained by tuning the number of printed layers, which fixes FSS resistivities, hence the absorption bandwidth. An electrical equivalent circuit is proposed to explain the absorption mechanism. Excellent agreement is observed between the designed and measured low reflectivity and high absorption. The absorber stands out in term of bandwidth and compacity as compared to the state of the art.