Research on Local Sound Field Control Technology Based on Acoustic Metamaterial Triode Structure

Round 1

Reviewer 1 Report

This manuscript is about designing acoustic triode using acoustic metamaterial, and this subject is suitable to the journal. However, the reviewer could not get the main idea of the paper, and suggests the authors to rewrite it thoroughly and to proofread the manuscript thoroughly with a professional English assistance for a publication. The reviewer suggests a major revision and requests the answers to the questions and comments  below.

1. The written English requires a thorough proofreading. Examples include followings.
   199. Some sentences are grammatically wrong and thus very difficult to read, such as L106-108, L 138-139, and L197-199.
   200. Not enough explanation such as L 165-167
2. In Section 1, it seems that the main idea is to amplify and deliver ultrasonic wave from a cell excited by a laser pulse for photoacoustic detection. If this method is used only for the photoacoustic detection, the introduction requires more explanation about the detection methods such as how low is the acoustic pressure, what the frequency range is etc. Otherwise, investigating other possible applications will be very helpful to readers.
3. Does the term ‘high-frequency’ in the paper mean ultrasonic? The reviewer suggests to stick to one term for one definition.
4. 1b seems a part of Fig. 1a. There is no such description. Are the two figures all acoustic triode model and artificial periodic structure model or not?
5. 1b does not look like a periodic structure.
6. In L95, the dimensions are not clear. Is the outer diameter 0.7mm? what is “the size”? Is it the diameter of the steel bar?
7. L105: The frequency is 274 kHz. It seems the frequency range is important but there is no explanation about the frequency. Can you explain why the frequency is selected?
8. L105: In addition, 2 Pa is within the reason of actual sound pressure from a cell excited by a laser pulse? Why did you choose 2 Pa?
9. In Fig.2, correct the captions.
10. In Fig. 2b, what is this showing? What is normal condition? Sound wave transmission from where to where?
11. L 114: Do the red and blue colors mean the colors in the color bar? What does the sentence ‘the sound pressure in different direction’ mean?
12. L116: the sound pressure can reach 20 Pa. The reviewer cannot understand how it can reach 20 Pa with the two 2 Pa sources. Is the metamaterial resonance-based? Is the mechanism explained in the text?
13. L117: the sentence does not make sense. “the sound wave energy … greatly improved” ? What is “the defect” ? Did you ever mentioned “wave transmission energy loss” before?
14. L118: The authors must explain what is the normal condition.
15. L120: now it reaches to 60 Pa. How is this possible with two 2 Pa sources? Similar to the question # 12.
16. In Fig. 3, it is very difficult to see what the graph is showing. What is the x-axis referring? The label says length. Which length is it? There is no explanation about the axis in the manuscript.
17. Although the reviewer cannot understand what it is, Fig. 3 seem important to authors. However, there is no in-depth explanation about it.
18. 4 shows simulation results with 4 different frequencies. Are they arbitrarily chosen? Are they related to the photoacoustic detection? Could you explain why they are selected?
19. In Fig. 4b and 4c, the two frequencies are 1 kHz different, and the simulation results seem very similar. Is there any reason that the authors choose these similar two examples in the figures?
20. L 150: The authors say “similar effect”. The reviewer cannot agree with it because there is no proof, no explanation about the effect in the figure and the manuscript.
21. L 151: the authors say “same sound wave transmission phenomenon”. What does this mean? Does this mean the four simulation results in Fig. 4 are showing same phenomenon? But they look different to the reviewer. Did you show the figures to readers in order to prove that they are the same? Need much more explanation.
22. 5: same to question # 16.
23. In Fig. 5, although it is difficult to see what they are, I believe that the authors must’ve tried to show some valuable results. However, the reviewer cannot find any in-depth explanation of the results in the manuscript. Please explain the results in the manuscript.
24. L164-168: The reviewer cannot understand any of the sentences. Does this mean that the pressure values are increased but differently? then what does “but the effects are different” means? Please rewrite it and explain more about it.
25. The reviewer’s questions above are about sections up to 4.1. The reviewer cannot continue to read it without understanding the stories up to the section. Please consider the questions above for the other sections in the manuscript as well.

Author Response

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Reviewer 2 Report

The manuscript “Research on local sound field control technology based on acoustic metamaterial triode structure” presents a study of wave propagation in the triode model with periodic manmade structures, with an emphasis on application to cell photoacoustic detection. The authors carried out numerical simulations (not experiments) to improve the weak acoustic signal through the defect-based acoustic structure, and to show the blocking function with the phase interference. However, the current manuscript should be improved considering the comments:

1. The paper is not well written. I strongly recommend that this paper should be double-checked by a native speaker.
2. It seems that all figures are extracted directly by COMSOL software, even for 2D graph data. These figures are not up to the level of any scientific journals, therefore they should be edited in a scientific way.
3. I see the term “experiment” in the manuscript describing numerical simulations. The authors should clarify the use of terminology. Readers may misunderstand that this work would have carried out experiments.
4. The main system is a triode with the bulky periodic structures based on rubber and steel. Here, I don’t see how the model (rubber and steel) is chosen. Usually, defect-based phononic crystals with a single material (not composite like rubber+steel) have been investigated to guide acoustic waves. Moreover, the composite material (rubber and steel) may induce an internal local resonance interrupting the efficiency. Therefore, the authors perhaps explain more clearly about the model choice.
5. All phenomena are totally expected and the underlying physics in terms of metamaterials/phononic crystals is not improved at all, but this work shows the feasibility toward applications. In that sense, I would like to see the comparison between the normal Y-junction tube and the author’s suggestion. If the authors explain well about this comparison, then this work will be more highlighted.

Author Response

Thanks to the reviewer for your comments. We use word to upload comment responses. Please see the attachment.

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Round 2

Reviewer 2 Report

The queries are properly answered and reflected accordingly. I recommend this for publication. 

Only a minor comment is adding few recent references for acoustic metamaterials such as,

https://aip.scitation.org/doi/10.1063/1.5051439

https://nanoconvergencejournal.springeropen.com/articles/10.1186/s40580-017-0097-y