Dual-Band Terahertz Perfect Absorber Based on Metal Micro-Nano Structure

Round 1

Reviewer 1 Report

The authors have satisfactorily addressed most of the reviewers’ remarks and suggestions, and changed the manuscript accordingly. In particular, this reviewer was concerned with the presentation of the results and the overall quality of the figures and plots. The authors have addressed these issues satisfactorily and added to the manuscript more details regarding the choice of parameters and the full-wave simulation. They have also clarified the irradiation schemes used in the numerical simulations and excluded the solar radiation absorption from the possible applications of the proposed metamaterial.

Overall, although the manuscript still needs a lot of correction regarding style and text editing, the study presented by the authors seems technically correct and could be of interest to the readers of Coatings.  For this reason, this reviewer recommends its acceptance for publication.

Author Response

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

good work!

Only a little suggestion: could you remove outlined text?

Author Response

Response to Reviewer 2 Comments

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript under review entitled " Dual-band terahertz perfect absorber based on metal micronano structure " reports on a theoretical study of a sub-wavelength range-based dual-band tunable terahertz metamaterial perfect absorber. The proposed absorber structure consists of three main layers, with the absorber layer consisting of a metal I-shaped structure.

The subject of the paper considered is noteworthy and the manuscript is reasonably structured and organized. However, the introduction does not give a satisfactory literature survey on a similar topic.

In short, there are still some problems. It can be considered to be published after revisions. My comments and questions are listed as below:

1. Other than numerous instances of poor grammar and a number of sentences without a verb, the paragraph/sentence describing the obtained results in the presented work is repeated several times at different places in the manuscript.
2. The figures in the paper are not clear. The size of the figures should be improved and their quality could be improved.
3. It is thought that the novelty of the proposed absorber structure has not been discussed (deeply and in detail) enough by using references in the introduction section. In addition to the existing references, some up-to-date references must be given in this section.
4. For the construction and principles of the proposed absorber, the authors should explain why the absorber layer consists of a metal I-shaped structure? Why did the authors choose metal I-shaped structures?
5. The authors mentioned that the structure of the metamaterial perfect absorber consists of five layers. Such structure gives absorption peaks for the two polarization states in the terahertz band. However, various photonic crystal structures have already been well proposed for the realization of the multi-channel perfect absorber, including photonic crystal cavities and one-dimensional topological photonic crystal heterostructure (Wang, X., Liang, Y., Wu, L., Guo, J., Dai, X., & Xiang, Y. (2018). Optics letters, 43(17), 4256-4259, Kassa-Baghdouche, L. (2019). Physica Scripta, 95(1), 015502, Kassa-Baghdouche, L., Boumaza, T., & Bouchemat, M. (2015). Physica Scripta, 90(6), 065504.). Such structures should be included in the introduction of the manuscript. Moreover, the difference between these structures and the proposed structure should be included in the manuscript.
6. In the second section (Unit structure and simulation methods), the authors give the values for the geometrical parameters of the metamaterial perfect absorber designed in the paper. Why do the authors choose such values for the geometrical parameters (the thickness of the first, second, and fourth layer) ?
7. In the third section (Results and Discussion), the authors studied the relationship between the thickness of the metal absorber layer and the absorbance of the metamaterial structure. The relationship between the thickness of the SiO2 dielectric layer and structural absorbance. The relationship between the incident angle of the incident electromagnetic wave and structural absorbance. The authors should derive a mathematical model for these relationships.
8. In the third section (Results and Discussion), it is better to have a table when making a comparison with some other similar absorber devices.
9. In this manuscript, only numerical studies of the absorber were performed and any experimental results were not given. If the numerical results (Section 3) of this study had been extended with additional experimental results, it would be better.

Author Response

Response to Reviewer 3 Comments

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have implemented my suggestions. I recommend this manuscript should be accepted for publication.

I would not like to sign my review report

Please do not publish my review report and my name alongside the accepted manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Dear authors,

this simulation work is interesting. I have only a suggestion. This structure can be effectively utilized for terahertz imaging and detection, but not for solar absorption (as you propose in the conclusion) because the solar radiation absorption requires a nanostructured metamaterial (as you correctly cite in introduction [1-2]). Metamaterials are artificial media that can be tailored in different spectral ranges, and those you propose are idoneous in Thz but not in visible and solar  range.

Reviewer 2 Report

Using simulations based on finite element analysis, the authors have proposed a terahertz metamaterial absorber consisting of a three-layer metal-insulator-metal microstructure. The main idea was to investigate a layered metamaterial where the top layer was patterned in four I-shaped microstructures.  To this end, they have considered two layers made of gold with a silica layer acting as a dielectric spacer irradiated by TM and TE plane waves in free space. They have obtained absorption efficiency of 99% for two peaks in the terahertz frequency range for normal incidence. They have also studied the robustness of the metamaterial absorber regarding the geometric parameters of the layers, polarization and incidence angle of radiation, obtaining good results for angles smaller than 40 degrees.

Overall, the manuscript needs a lot of improvement in the writing and the English usage. More importantly, the proposed metamaterial absorber should be compared with other approaches using I-shaped resonators (see, e.g., Optics Letters 37, 154-156, 2012). For instance, it could be included in the manuscript a discussion of the advantages and shortcomings of the authors' design compared with the aforementioned reference using the same I-shaped structure.

In conclusion, this reviewer believes that the manuscript needs a lot of improvement in the presentation and discussion of the results, and does not recommend its acceptance for publication in Coatings. The authors are suggested to consider the comments below.

• The irradiation scheme and polarizations used in the simulations are not clear. In fact, the authors have not defined in the manuscript the TE and TM modes associated with the incident electromagnetic wave.
• In Fig.2, the absorption curves seem to be calculated for the electromagnetic waves interacting with the metamaterial absorber (TE and TM modes) and not for the electric and magnetic fields separately. The authors should clarify this issue for the benefit of the reader. In fact, both the electric and magnetic field distributions should be presented for the TE and TM modes in Fig.2.
• Figure 3 suggests that the electric field is polarized along the y axis for the TE mode (Figs.3 a and c) and along the x axis for the TM mode (Figs.3 b and d). Again, the plots do not seem to show the electric and magnetic field distributions separately.
• The overall quality of the plots presented in the manuscript should be improved. In particular, the font size used in the figures is not readable in the printed version and is pixelated.  

Reviewer 3 Report

General comments:

In the article titled “Dual-band terahertz perfect absorber based on metal micro nano structure” propose a sub-wavelength range-based dual-band tunable ideal terahertz metamaterial perfect absorber. This article study the absorption peaks by simulating the incident wave absorbance. Moreover, the other parameter including the relationship between structural absorbance and structural geometric parameter, the relationship between the thicknesses of the metal absorber layer, and the relationship between the thickness of the SiO2 dielectric layer and structural absorbance has studied also. However, for a better understanding it should be integrated considering the following aspects:

1. The author highlight several previous works that there is the other work have achieve perfect absorption. However, I could not see the frequency and absorbance value. Please add the previous works with frequency and the absorbance achieved. In addition, please explain the novelty of the study in detail because I am unable to see the impact of this study especially compare to the previous study including:

https://doi.org/10.1038/s41598-022-04772-4

https://doi.org/10.1016/j.rinp.2019.102603

https://doi.org/10.3390/mi12111290

2. Please justify why several the geometrics values are chosen. Why the h₁ layer thickness must 16 μm, the h₂ layer thickness 15.5 μm and also the other values, please explain.
3. I am unable to find the software used in this study which are for simulation and for design. Please explain.
4. The author state that achieve a strong magnetic response at 6.35 THz and a weaker magnetic response at 8.05 THz due to the higher frequency, resulting in a weaker magnetic field absorption at 8.05 THz. However, this phenomena is not explain in detail.

Comments for author File: Comments.docx