Comment on Dual-Band Perfect Metamaterial Absorber Based on an Asymmetric H-Shaped Structure for Terahertz Waves Materials (2018) 2193; https://doi.org/10.3390/ma11112193

摘要

In a recent publication, Lu et al. [ ] proposed a dual-band perfect metamaterial absorber based on an asymmetric H-shaped structure for terahertz waves. The authors claimed 99.95% and 99.91% absorptions at two resonance frequencies of 4.73 THz and 5 THz, respectively. In this paper, we demonstrate that the authors erroneously interpreted cross-polarizer as a dual-band absorber. By including both polarized reflection coefficients (co- and cross-), the absorption decreases from 99.91% to 21% at 5 THz. However, absorption remains at 99.95% at 4.73 THz but disappears when FR-4 (lossy) substrate is used. It is worth mentioning that the authors designed the absorber on FR-4 (loss-free) substrate, which is commonly used in ideal conditions. We analyzed the results for both lossy and loss-free FR-4 substrate. Additionally, the polarization conversion ratio (PCR) is approaching 85% at a resonance frequency of 5 THz, which shows that the proposed metasurface is a cross-polarizer rather than an absorber.