Comment on “An ultrathin and broadband metamaterial absorber using multi-layer structures” [J. Appl. Phys. 114, 064109 (2013)]

Abstract

In a recent publication by Xiong et al. [J. Appl. Phys. 114, 064109 (2013)], a linear cross-polarizer is erroneously interpreted as a broadband absorber with a claimed absorptivity above 90% over a frequency range of 8.3721 GHz. In this article, the authors have presented an investigative study demonstrating that the structure proposed by Xiong et al. is actually an efficient cross-polarizer rather than a perfect absorber. If we consider both co- and cross-polarized components of the reflected electromagnetic wave, the subject absorber provides less than 20% absorption in the claimed band. In addition, the polarization conversion ratio of the structure is above 85% within the operating band, this makes the subject metasurface a potential candidate for applications where high-efficiency cross-polarization is desired.

Comment on Lu et al. Ultrathin Terahertz Dual-Band Perfect Metamaterial Absorber Using Asymmetric Double-Split Rings Resonator. Symmetry 2018, 10, 293

“…It remains a challenge to achieve wide-band absorption using single-layer periodic structures. While there are several single-layer designs reported in the literature that researchers claim to be absorbers [5][6][7][8][9][10], they are cross-polarizers [11][12][13][14][15] in reality. These articles only consider the co-polarization component of the reflected wave in their analysis and mistakenly conclude that their structures are perfect wide-band absorbers.…”

Design of an optimized multilayer absorber into the MWIR and LWIR bands

“…On the other hand, due to the inherently resonant behavior of the periodic metamaterial layer, good matching tends to be limited in a relatively narrow frequency band; to achieve dual‐band absorption, multiresonance metamaterial absorbers combining more than one resonant element in each array cell may be used 11 . More complicated multilayer structures, (e.g., in References 12,13,16) have also been proposed for extended absorption bandwidth in microwave and THz regimes, but are difficult to fabricate in smaller dimensions required for infrared regime, while it has also been pointed out recently (see e.g., the Reference 24) that some such designs actually tend to cross‐polarize rather than absorb a significant portion of the incident power. Alternative approaches make use of pyramidal‐shaped resonant elements 14‐16 .…”