Reflection-less frequency-selective microwave metamaterial absorber

We present a subwavelength-thick reflection-less metamaterial absorber that shows frequency-selective narrow-band near-perfect absorption at 2.4 GHz. The absorber does not have a ground plane and is constructed with a square array of pairs of C-shaped split-ring resonators (SRRs) orthogonally arranged in such a way that induced electric and magnetic dipoles destructively interfere and no reradiation of electromagnetic (EM) waves is observed. The SRRs are made of nichrome with high ohmic loss so that EM energy dissipates as heat. We numerically determined the optimum geometrical parameters of SRRs, and absorption of 97% is achieved at 2.4 GHz. We also fabricated a device using nichrome wire and obtained a huge decrease in transmission at a resonance of –6 dB with no reflection over the entire frequency range of interest. Our basic concept can be extended to higher frequency ranges and may be utilized for next-generation wireless communications, the Internet of Things (IoT), and so forth.