Dual Circularly Polarized Encoding Terahertz Tag with Linked-Semi-Ellipses Elements

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the authors demonstrate a dual-polarized THz design that could be used as a identification RFID tag. This basic elements of the design is a linked semi-eclipse element and the polarization conversion principle is due to the rotation-induced geometric phase. Finally, the author propose a full design to achieve 2-bit circular polarizatio encoding using 9 basic elements as a state. 

The concept is novel for the application of RFID tag. The design concept is solid as the geomtric phase has been widely used in various areas. The authors present concrete evidence analytically and numerically to show the validity of the design. Therefore I recommend the article to be published. However, there are a few points that I think the author should address to improve the article:

1. In line 150-161, the authors discuss the dispersion characteristic of the elements. However, there is no figures related to the context. I think the authors need to add more figures to demonstrate the change of the primary current distribution.
2. Figure 7 and Figure 8 could use a 'wrapped phase' instead of absolute phase difference to show the 180 deg phase change. 
3. In the identification tag design section, could you provide more motivation on how this design is proposed? Could you give more theoretical analysis that whether this design could provide the maximum contrasts?
4. The author should compare with the simulated results in other articles that are targeted for the same application.

 

Comments on the Quality of English Language

1. Sometimes the word is misleading. For example, in line 73, the author states that "The geometric phase element has polarization conversion capabilities". However, the discuss of the "polarization conversion" part is in line 78-81. This confuses the reader.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a dual circularly polarized coding terahertz tag based on linked semi-elliptical Elements. its effectiveness was verified through simulations. The study is of some innovation and can be accepted after minor revisions. Comments are below.

1. The study lacks comparison with other terahertz tags. It is recommended to compare key performance metrics such as polarization conversion rate, bandwidth, and radar cross-section (RCS) with similar designs. Also,
2. Has the tag been fabricated? If not, the authors should explain why or provide a fabrication suggestion.
3. The study only examines the effect of d1 and d2 on tag performance. It would be helpful to analyze other parameters, such as the major and minor axes of the semi-ellipse, to provide a more complete understanding and guide further optimization.
4. The optimization process of the simulation should be clarified. Was a specific algorithm used? Were the simulations repeated to ensure stable results?
5. The manuscript mentions potential uses of circular polarization encoding in recognition systems but does not explain specific applications like indoor positioning or object identification. Adding details on practical usage would enhance the study’s impact.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors present a simulation-based study on a dual-tag configuration operating in the sub-THz frequency range. The proposed tag leverages circular polarization for encoding, and the manuscript effectively demonstrates the simulation results. However, the overall strength of the work is diminished due to the absence of experimental validation to support the simulation-based claims.

1. The working principle of cross-polarization is clearly explained in the introduction. However, the introduction would benefit from additional references showcasing the application of linearly polarized tags in various use cases. A strong example can be found here: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=9264219. Additionally, the inclusion of a comparative figure illustrating the working principles of linearly and circularly polarized tags would significantly improve reader comprehension.

2. In Section 2, please clearly define all notations used in the text for clarity and completeness.

3. Regarding the explanation of matrix element M2(2,2), it is unclear why a phase shift of 270° is observed instead of 90°. This should be clarified with further theoretical justification.

4. Section 3 describes the patch design as consisting of two semi-elliptical shapes connected by a strip line. However, the rationale behind choosing semi-ellipses over other geometries, such as circular or rectangular shapes, is not provided. Please elaborate on the design choice and its impact on performance.

5. The selection of quartz as the dielectric substrate should also be justified. Why was quartz chosen over commonly used materials like Rogers or FR4?

6. For Figure 5, please include two additional subfigures showing the phase variation with respect to the 0 μm case for both d1 and d2. While the authors mention that “At 0.45 THz, the phase variation with d2 is approximately 169.8°/μm, while the dispersion variation with d2 is -6.1°/(THz·μm)”, this is not readily apparent from the current figures.

7. Further clarification is needed on why variations in d2 lead to greater dispersion sensitivity than d1.

8. Figure 6 indicates that the maximum bandwidth occurs when d1 and d2 are 0 μm. However, Table 1 lists the optimized values of d1 and d2 as 25 μm and 10 μm, respectively. Please explain this discrepancy and how the optimized values were determined.

9. It would be beneficial to include a clear explanation of how polarization conversion efficiency is calculated to enhance reader understanding.

10. Please update the figures to use proper scientific notation, particularly for units such as dBm², by using subscripts instead of carets (e.g., dBm² instead of dBm^2).

11. The figures illustrating the simulated RCS pattern vs. angle and vs. frequency should be revised for clarity. Specifically, use one consolidated figure to show the RCS pattern vs. angle for states 00, 01, 10, and 11, and another figure to show the RCS pattern vs. frequency for the same states. This will improve the manuscript’s readability and comparison.

12. The proposed system requires eight tags to represent four states. This raises a fundamental question, as digital encoding typically allows for 2^n states. Is this a limitation of the current approach? Please address this point in the discussion.

13. In the conclusion section, include a comparative table listing the performance of the proposed tag against state-of-the-art chipless tags, incorporating encoding capacity as one of the comparison metrics.

14. Lastly, and most critically, the manuscript lacks experimental validation, which is essential for evaluating the real-world applicability of the proposed tags. Adding experimental results would significantly enhance the credibility and impact of the study.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1. The paper proposes a dual circularly polarized coding terahertz tag using linked-semi-ellipses, which could be a valuable addition to metasurface-based tag technologies. However, to strengthen the impact and clarify the novelty, a more thorough comparison with existing approaches would be helpful. Highlighting what sets this work apart in terms of performance, structure, or application will significantly enhance its contribution.

2. A more detailed explanation of how the geometry enables polarization control could offer readers better physical insight and increase the technical depth of the paper.

3. The technical content of the paper is promising, but clarity is occasionally hindered by grammatical issues and vague expressions (e.g., "less affected by environmental"). A careful proofreading and revision with attention to technical language would improve readability and strengthen the communication of the results.

4. The simulation results are encouraging and show good performance in terms of polarization conversion and RCS reduction. Including a brief discussion on the feasibility of fabrication or planned experimental validation would greatly increase the practical relevance and completeness of the study.
5. The reported results—such as polarization conversion efficiency and beamwidth—are promising. Including a quantitative comparison with recent works would help to clearly showcase the strengths of the proposed design and support the authors’ claims regarding performance advantages.

6. The application to identification systems is compelling. The manuscript could be further enhanced by outlining a practical use case or integration scenario to demonstrate the real-world potential of the design. This would give readers a clearer sense of the broader significance and impact of the work.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have thoroughly addressed all comments and questions raised by the reviewer. Good work.