Review Reports

Round 1

Reviewer 1 Report

I have reviewed the manuscript entitled “Tunable Beam Splitter Based on Acoustic Binary Metagrating”. This manuscript is based on the comprehensive study of beam splitter based on an acoustic binary metagrating (ABM) constructed by etching one straight-walled groove per period on a planar hard surface. It gives rise to reduced intrinsic loss and easy fabrication. The manuscript may be interesting for the readers of this area. Therefore, I recommend it for publication in its current form.

Author Response

Response to Reviewer 1 Comments

 Point 1: I have reviewed the manuscript entitled “Tunable Beam Splitter Based on Acoustic Binary Metagrating”. This manuscript is based on the comprehensive study of beam splitter based on an acoustic binary metagrating (ABM) constructed by etching one straight-walled groove per period on a planar hard surface. It gives rise to reduced intrinsic loss and easy fabrication. The manuscript may be interesting for the readers of this area. Therefore, I recommend it for publication in its current form.

Response 1: We are strongly encouraged by the reviewer’s report that the paper can be published in its current form. Thank you!

Author Response File: Author Response.pdf

Reviewer 2 Report

The conclusions paragraph is missing at the end of the paper.
You have only used numerical models with the comsol software, but you have not performed any tests to validate your theory with experiments in the laboratory or in the field.
The paper as it is written is very weak to be accepted for publication in the journal

Author Response

Response to Reviewer 2 Comments

Point 1: The conclusions paragraph is missing at the end of the paper.

Response 1: We thank the reviewer for raising this valuable point, which gives us the opportunity to improve the manuscript. Following the reviewer’s suggestion, we have added the conclusion paragraph at the end of the paper on Lines 364-376: “In conclusion, we have demonstrated the beam splitter based on the ABM, which is constructed by etching a wall-straight groove per period on the planar hard surface. The structure of ABM in our proposal gives rise to the reduced intrinsic loss and the easy fabrication. The diffraction orders in the proposed ABM take a value of n = -1 (split beam 1) and n = 1 (split beam 2), and hence, the beam splitting occurs. In our design, the directions of the split beams can be readily controlled by setting a proper incident angle. Theoretical analysis and numerical simulations are provided to give the proof of concept for the proposed acoustic beam splitter. In the proposed ABM, the beam splitting occurs when the period length a is in the range of  and the incident angle  is in the range of . For example, in the case of , the beam splitting occurs when . In the case of , the beam splitting occurs when . The proposed beam splitter based on the ABM may has potential applications in information processing and biomedical diagnostics.”

Point 2: You have only used numerical models with the comsol software, but you have not performed any tests to validate your theory with experiments in the laboratory or in the field. The paper as it is written is very weak to be accepted for publication in the journal

Response 2: We thank the reviewer for the careful review and pointing out this important point.

First, it should be clarified that experimentally reproducing this work is technically feasible. The experiment setup should be built in a planar waveguide system with the 3D-printed ABM firmly sandwiched. The absorbing foam should be placed surrounding the planar waveguide to avoid the reflections from the boundary of the planar waveguide system. The pressure field can be scanned by the microphone. However, it is a great pity that there is no necessary equipment in our research group to conduct the experiments for this moment.

Despite that, we would like to emphasize that this work is still valuable and worthy of the publication. The metasurfaces, which leads to a number of unique functionalities which cannot be realized by the conventional materials, are the promising and hot topics in acoustics. However, the typical design of the subwavelength unit cells on the acoustic metasurfaces are usually constructed by the multi-folded channels or multi-connected cavities of a deep subwavelength scale. It gives to the elaborated configurations, inevitable loss and deformation effects. Our proposed ABM here is constructed by etching only one straight-walled groove per period on a planar hard surface. It leads to the reduced intrinsic loss and easy fabrication. In addition, the previous beam splitter is only designed for the normal incidence [Phys. Rev. B 2019, 100, 104104]. In our design, the beam splitting occurs in a broad incident angle range. Our work not only proposed the design of an ABM with the reduced intrinsic loss and easy fabrication, but also realized the beam splitting in a broad incident angle range. It exhibits the beam splitting when the incident angle is in the range of  in the case of  and when the incident angle is in the range of  in the case of .

In fact, our research group are eager to build the experiment platform. We are actively promoting the building progress. Once the experiment platform is built, this work will be experimentally reproduced.

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper “Tunable Beam Splitter Based on Acoustic Binary Metagrating” concerns a very interesting acoustic solution which is able to split acoustic wave into two predesigned directions under precise but tunable conditions. The model is well represented as well as the results; in conclusion, the paper is well written. However, minor but necessary adjustments must be done before publication:

• Line 51: is an ABM model firstly introduced by the authors? Or similar models are still available in literature? In the first case, please underline it; otherwise, insert specific references which report readers to the state-of-the-art.
• Line 75: 1 has a well described caption, but some important information should be inserted in the text as well. Please respect this general rule for each figure description.
• Line 99-109: this part needs an improvement: theory besides it must be described with more details (i.e., acoustic-electromagnetic equivalence). FE model should be better explained, maybe adding useful images of the numerical model. Last but not least: references must be put for each theoretical assumption even for FEM pre-implemented boundary conditions. You will enable readers to re-build the mathematics besides the problem.
• Line 118: please do not use square brackets for equation calls.
• Line 147-158: third person is highly recommended; please do not use first person.
• Line 243-253: few grammar and orthographical errors; not a big deal.

General tip for the paper: authors should emphasize the originality of their work.  Their results seem quite good, but it is not clear for what, how and where their beam splitter can be a solution better than other acoustic meta-surfaces, because not a true comparison was proposed. Furthermore, conclusions can be extended with more details: for example, in line 268 authors mentioned that “ABM has potential applications in information processing and biomedical diagnostics”; maybe it is better to justify this sentence and add more about it.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

improve refernces (see e.s. Ciaburro et al)

Author Response

Response to Reviewer 2 Comments

 

Point 1: Improve references (see e.s. Ciaburro et al)

 

Response 1: We thank the reviewer for carefully reading our manuscript and raising this important point, which provides us an opportunity to improve our manuscript. Following the reviewer’s suggestion, we have added DOI for all the references. In addition, all the misstatements have been corrected. For example, in Ref 10 on Line 407, the title of “Acoustic Focusing and Energy Confinement Based on Multilateral Metasurfaces” has been corrected as “Acoustic focusing and energy confinement based on multilateral metasurfaces”.

Author Response File: Author Response.pdf