Detection of Benzoic Acid Additive Based on a Terahertz Metasurface Sensor

Round 1

Reviewer 1 Report

The paper describes a plasmonic sensor based on metasurface with a resonant absorption peak around 930 GHz. This feature can be used to detect benzoic acid since its molecule has vibrational modes with the same eigen frequency. This approach could be extended to other substances although authors don’t discuss this opportunity. The paper is worth publishing after some minor corrections

1.      Term RIU in the abstract has to be explained right away in the abstract and introduction

2.      Fig 2 a should specify the W value for which the transmission curves with different L were obtained

3.      Similalrly

4.      Fig 2 b should specify the L value for which the transmission curves with different W were obtained

5.      Both figures should contain the T(Frequency curve) with the same L,W set so that th reader can see which parameter change affect the curve more

6.      Figure 5 caption has to be corrected

7.      Section 4 has to be renamed to “Conclusions” since it is nothing but a short summary of the previous section. Section 3 could be named “Results and discussion”

Author Response

Author Response File: Author Response.doc

Reviewer 2 Report

In the present work, the authors proposed a metasurface sensor that works in the terahertz band and is used for the detection of benzoic acid additive. Nonetheless, the overall quality and innovation of this manuscript should be further enhanced, which may not meet the standard of the journal, therefore, it is not sufficient to recommend for publication in this case, or major modifications should be implemented at least.

1.       The conductivity of aluminum used in simulation should be given.

2.       Some of the simulation settings are written in the third section, while some of the results are written in the second section, so the full text needs to be reordered.

3.       The electromagnetic properties of benzoic acid, i.e., the permeability, should be given when using CST to simulate the sensing performance of the proposed terahertz metasurface sensor.

4.       How do structural parameters affect the transmission spectrum of the proposed terahertz metasurface sensor? Further mechanistic explanations, such as equivalent circuit model, are needed.

5.       The interpretation of the peaks produced in the transmission spectra after the addition of benzoic acid by using HIT theory requires more in-depth discussion. Why higher concentration of benzoic acid analyte enhanced transmission rather than weakened?

6.       The authors simply present a model of the relationship between the transmission intensity and thickness of benzoic acid additives, but the metrics used to assess the accuracy of this model, such as the correlation coefficient and root mean square error, are not given, which needs to be added.

7.       What is the lower limit of detection of the proposed terahertz metasurface sensor for benzoic acid additive? Is it possible to meet the detection limits of national standards?

8.       Experiments need to be added to verify the accuracy of the simulation. Besides, can the proposed terahertz metasurface sensor be used to detect benzoic acid additive in food products such as edible oils and flours, not just different amounts of pure benzoic acid.

9.       More comparisons of benzoic acid additive detection performance to the previous works should be given in the paper, as there have been similar reports of benzoic acid additive sensing using terahertz metamaterials, such as [Sensors, 2021, 21(9), 3238], [Infrared Phys. Technol., 2022, 123, 104101] et al. What are the performance improvements of this job compared to those jobs?

10.    The innovation of this work should be highlighted.

the language should be improved by moderate editing.

Author Response

Author Response File: Author Response.doc

Reviewer 3 Report

The submitted paper “Detection of benzoic acid additive based on a terahertz metasurface sensor” by

S. Ma, F. Li, Y. Su, L. Chen, Y. Song, J. Ye is devoted to CST studio modeling of electromagnetic response (current and field distribution, and differential transmission) of a metasurface with benzoic acid analyte. The importance of designing of benzoic acid sensors is highlighted and the subwavelength metasurface structure is proposed as an efficient one. The obtained results seem to be new, but the study would be much more valuable with experimental realization and measured THz transmission/reflection spectra. There is no Conclusion section and the discussion section is too short. Something should be said why crosses were chosen as elementary unit and not split ring resonators or squares. Is it possible to get resonance dips about 0.95 THz using such elements? Was the terahertz transmission spectra of separate benzoic acid layer of 3-8 mkm thickness measured or modeled? How large are reflection and absorption  losses compared to observed variation in differential transmission intensity (not shown in Fig. 4). Which cross length and width were used to get curves in Fig 4? Why the resonance dip splits into two dips?

In my opinion, the submitted paper could be published in Photonics only after improvement of these issues.  

Author Response

Author Response File: Author Response.doc

Reviewer 4 Report

This paper reports that a terahertz metasurface sensor model can be used to detect trace amounts of benzoic acid with good sensitivity, which has applications in the field of food safety.

However, from the scientific point of view the paper lacks of several important aspects, necessary to be solved. The questions have been listed as following:

1.      What are the main ways in which benzoic acid is currently detected in the food sector? The relationship between the thickness of benzoic acid and the resonance peak is analysed in the text, but the conclusion is that the concentration can be detected, so clearly "thickness" and "concentration" are not the same physical quantity and the authors should clarify this.

2. 为什么 是否选择太赫兹波段作为苯甲酸的检测带？一些先前 在修订稿中应增加考虑太赫兹超表面的研究（见 https://www.mdpi.com/2079-4991/11/12/3409 或 https://www.degruyter.com/document/doi/10.1515/nanoph-2022-0018/html），以丰富研究背景。

3. 作者选择聚酰亚胺作为超表面传感的基板和 设计厚度为108μm。众所周知，聚酰亚胺是一种聚合物 材料。在这样的条件下，它的弯曲和起皱是否会影响传感性能。 厚度小？

4. 在第 73 行中，“3.5 （）”应为 改为“（3.5）”; 应写第 140 行括号中的内容。

5. 请 仔细阅读论文的英语语言风格和准确性，并制作 适当的更正和更改。

请 仔细阅读论文的英语语言风格和准确性，并制作 适当的更正和更改。

Author Response

Author Response File: Author Response.doc

Round 2

Reviewer 2 Report

the authors have addressed all my previous concerns and can be published on this journal.

moderate english editing is necessary for the manuscript

Reviewer 3 Report

I think the performed improvements of the text and explanations are good enough, the paper could be accepted for publication.