Chiral composite metamaterials with gradient phase index for vortex electromagnetic−wave generation and attenuation

Abstract

The conversion of incoming electromagnetic-waves into vortex waves by electromagnetic-wave absorption materials (EAMs) is expected to improve the absorption properties, but remains elusive that direct conversion of linearly polarized waves into vortex waves to breakthrough the angular momentum mismatch. In this context, we fabricate chiral composite metamaterials with gradient phase index to realize the mentioned conversion. The chiral composite metamaterials generate vortex waves with topological charges of ± 1 and ± 2 within broad bandwidth from linearly polarized waves, and the arrangement of meta-atoms with different geometric phases manipulate the chirality of vortex waves. Vortex zero of the electric field vector appears near the phase singularity, which induces the far-field diffusive nature of the vortices to enhance absorption. The best absorption peak value of − 33.55 dB is achieved with a topological charge of + 1. Optimal effective absorption bandwidth (reflection loss (RL) ≤ −10 dB) appears when the topological charge is + 2, which reaches 10.97 GHz (7.89 −12.21 and 29.31 −35.96 GHz). Present works provide a research path for the development of novel metamaterials and EAMs.