Challenges and solutions in designing broadband metamaterial absorbers based on coplanar arrangement of resonators

Coplanar metamaterial absorbers have been investigated extensively in literature, however, there are still various hidden issues related to their optimum designs, which prevent successful achievement of coplanar broadband metamaterial absorbers (BMAs). In this work, we investigate three key challenges to achieve the best performance of coplanar BMAs, which are (i) unexpected shifts of magnetic resonant wavelengths induced by the gap coupling effect; (ii) low absorptivity caused by inappropriate filling rate of resonators; and (iii) diminished absorptive spectra incurred by hybridization between magnetic resonance (MR) and surface plasmon resonance (SPR). To improve the optimum coplanar designs of BMAs with excellent performance, we provide the corresponding solutions to these problems including: (a) setting a gap larger than the critical value to prevent the gap coupling effect or calculating precisely the magnetic resonant wavelength by the correct prediction equation covering the gap coupling effect; (b) designing resonators with smaller feature sizes and/or to reducing the gap to its critical level; and (c) avoiding or weakening the hybridization of MR with SPR by adjusting their relative positions.