Ultrasonic Non-Contact Air-Coupled Technique for the Assessment of Composite Sandwich Plates Using Antisymmetric Lamb Waves

Round 1

Reviewer 1 Report

The paper titled "Ultrasonic Non-Contact Air-Coupled Technique for the Assessment of Sandwich Composite Plates Using Antisymmetric Lamb Waves" is currently deemed unsuitable for publication due to several critical issues:

1. The authors should articulate the distinctiveness and novelty of their work within the abstract and introduction sections. Absent such delineation, the paper risks being perceived as an academic exercise rather than a substantial research contribution.

2. The quality of figures presented within the manuscript is suboptimal. We recommend the utilization of vector graphics instead of screenshots for enhanced clarity. Figure 2 contains visible markers from grammar checkers, which is not congruent with accepted publishing standards.

3. A comprehensive text refinement is imperative to rectify linguistic anomalies, such as the presence of mojibake in the mathematical formula on page 4.

The utilization of the English language in this manuscript adheres to established standards of academic papers.

Author Response

The paper titled "Ultrasonic Non-Contact Air-Coupled Technique for the Assessment of Sandwich Composite Plates Using Antisymmetric Lamb Waves" is currently deemed unsuitable for publication due to several critical issues:

1. The authors should articulate the distinctiveness and novelty of their work within the abstract and introduction sections. Absent such delineation, the paper risks being perceived as an academic exercise rather than a substantial research contribution.

 Answer 1.  It is correct your comment. Then in the new version, we expand the reference to 23 papers about the themes that we obtain from the web. We increase the novelty in the introduction and also in the abstract section. For instance, in Germany there are the papers from Hillger using a similar non-contact UT technology. But he recommends the use of FEM simulations in order to improve this technology.  This is what we do in this paper using the FEM technology together with the UT technology. We also proof the antisymmetric mode using the Phase velocity method. This was not considered by previous work in literature, which assumes this mode. (We saw the term lamb velocity, but which one?, group or phase velocity?

2. The quality of figures presented within the manuscript is suboptimal. We recommend the utilization of vector graphics instead of screenshots for enhanced clarity. Figure 2 contains visible markers from grammar checkers, which is not congruent with accepted publishing standards.

Answer 2, we improve the quality of all the figures to bmp.  We redraw many of them

3. A comprehensive text refinement is imperative to rectify linguistic anomalies, such as the presence of mojibake in the mathematical formula on page 4.

Answer 3. This was a mistake from the MDPI editor when they translate the manuscript, (that we sent in format docx,), to the template.doi. The new manuscript is done with the template from MDPI.

Comments on the Quality of English Language

The utilization of the English language in this manuscript adheres to established standards of academic papers.

Submission Date

07 September 2023

Date of this review

15 Sep 2023 06:10:10

Reviewer 2 Report

Comments for author : 

The authors proposed an ultrasonic non-contact air-coupled technique for the inspection of sandwich composite plates using antisymmetric Lamb waves. Although numerical and experimental investigations were conducted, I took the liberty to outright reject the article because of the following reasons:

1. The article lacks a statement of the current state-of-the-art regarding the inspection of sandwich composite plates using non-contact air-coupled transducers. It is imperative that the authors either expand upon this aspect or explicitly state if their work is the first attempt at inspecting sandwich composite plates via non-contact air-coupled transducers. If not, they should clearly articulate the novelty of the proposed technique compared with the existing
2. The resolution of the pictures in this manuscript is too low, especially in Figures 3a, 11, and 12. The authors should enhance the image resolution. Besides, in Figure 2, we can find the underlines below the words, i.e., “plate”, “Tx”, and “air”. These underlines appear to be unintended and should be More importantly, since the arrow in the plate represents the wave propagating direction, its thickness should not exceed the plate thickness.
3. The expression (2) is not accurately shown. The authors need to carefully double-check all the expressions before submitting the manuscript.
4. The authors compare the phase velocities at many frequencies for the free CFRP plate and sandwich plate by FEM in Figure However, only the experimental result at 250 kHz was measured in this case. I think more experimental data are needed to better illustrate the trend in phase velocities. Based on these results, the authors can draw a conclusion.
5. The format and style of the first reference differ from the rest. The authors should ensure consistent formatting and referencing throughout the

The authors may consider making these improvements before resubmitting the manuscript for further consideration.

Author Response

The authors proposed an ultrasonic non-contact air-coupled technique for the inspection of sandwich composite plates using antisymmetric Lamb waves. Although numerical and experimental investigations were conducted, I took the liberty to outright reject the article because of the following reasons:

1. The article lacks a statement of the current state-of-the-art regarding the inspection of sandwich composite plates using non-contact air-coupled transducers. It is imperative that the authors either expand upon this aspect or explicitly state if their work is the first attempt at inspecting sandwich composite plates via non-contact air-coupled transducers. If not, they should clearly articulate the novelty of the proposed technique compared with the existing literature.

Answer 1.  It is correct your comments. Then in the new version, we expand the reference to 23 papers about the themes that we obtain from the web, For instance, in Germany there are the papers from Hillger using  a similar non-contact UT technology. But he recommends the use of FEM simulations in order to improve this technology.  This is what we do in this paper using the FEM technology together with the UT technology. We also proof the antisymmetric mode using the Phase velocity method. This was not considered by previous work in literature, which assumes this mode. (We saw the term lamb velocity, but which one?, group or phase velocity?

2. The resolution of the pictures in this manuscript is too low, especially in Figures 3a, 11, and 12. The authors should enhance the image resolution. Besides, in Figure 2, we can find the underlines below the words, i.e., “plate”, “Tx”, and “air”. These underlines appear to be unintended and should be removed. More importantly, since the arrow in the plate represents the wave propagating direction, its thickness should not exceed the plate thickness.

Answer 2. It is correct your comments. We follow your recommendations, this means. We increase the resolution of the pictures; delete the underlines below the words in Fig. 2. The arrow also was adapted inside the plate.

3. The expression (2) is not accurately shown. The authors need to carefully double-check all the expressions before submitting the manuscript.

Answer3. This was a mistake of the MDPI editor, because we sent an original version in docx. Now we use the template from the MDPI and it is correct now.

4. The authors compare the phase velocities at many frequencies for the free CFRP plate and sandwich plate by FEM in Figure 10. However, only the experimental result at 250 kHz was measured in this case. I think more experimental data are needed to better illustrate the trend in phase velocities. Based on these results, the authors can draw a conclusion.

Answer 4. We agree that it could be convenient to use another frequency. The problems is that this work was a part of a European project, with a specific target  to obtain a UT non-contact method for gear body train. Then it was decided to develop a specific transducer for this purpose. Of course, in the future it could be increased. But in these moments, for the project, it was only necessary to develop one transducer with 250 KHz.

5. The format and style of the first reference differ from the rest. The authors should ensure consistent formatting and referencing throughout the article. The authors may consider making these improvements before resubmitting the manuscript for further consideration.

Answer 5.  As in the No 3, this was a consequence of the MDPI editor, which took our original docx document and translates to the template. In this new version the manuscript was adapted to the template.dot according to MDPI editors.

Round 2

Reviewer 1 Report

I have no further comments.

I have no further comments.

Reviewer 2 Report

The authors well addressed the issues. The manuscript can be published in the present form.