Hand Gesture Detection and Recognition Using Spectrogram and Image Processing Technique with a Single Pair of Ultrasonic Transducers

Round 1

Reviewer 1 Report

-The paper should be interesting ;;;
-add some photos about sensors, measurement - add arrows what is what;;;
-please add a block diagram of the proposed method;;;;
-please add a block diagram of the proposed research;;;; what is the result of the paper? 
-please add photos of analyzed faults
-please add photos of the application of the proposed research, 2-3 photos ;;; 
-please add sentences about future analysis;;;
-fonts of figures should be the same/bigger, ;;;
-add arrows, axes, labels what is what;;;;;
-formulas and fonts should be formatted;;;;
-references should be 2018-2021 Web of Science about 50% or more;; 30-40 at least.;;;;
-is there a possibility to use the proposed methods for other problems ? ;;;;
-please compare different methods advantages/disadvantages,
(search in Web of Science)
for example with image processing methods, thermal analysis:

1) 
Ventilation Diagnosis of Angle Grinder Using Thermal Imaging. Sensors 2021, 21, https://doi.org/10.3390/s21082853

-Conclusion: point out what are you done;;;;

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors propose a system to detect and recognise hand gestures with excellent results to avoid misdetection of other gestures. The proposed scheme is based on analysing the Doppler signals of hand gestures captured by means of a scheme composed of a pair of ultrasonic emitters and receivers and a signal processing circuit.

Considering the accuracy rate obtained by the proposal I recommend its publication in this journal, but some improvements are required before accepting it for publication.

1. In section 1 (introduction) the authors should discuss the usefulness of hand gesture detection systems. That is, in which fields is it an advantage to apply a hand gesture detection system? I think it is essential to justify the reasons for developing such detectors.
2. I recommend the authors to include the following reference as it is an article from 2020 in which a similar idea to the authors' is proposed.

Zhou, F., Li, X., & Wang, Z. (2020). Efficient High Cross-User Recognition Rate Ultrasonic Hand Gesture Recognition System. IEEE Sensors Journal, 20(22), 13501-13510.

3. Some equations have been included in image format. In particular equations 5, 6, 7, 8 and 9. This should be corrected before publication of the article.
4. The authors should include an analysis of the computational cost of the proposal. This allows justifying issues related to the time needed for the proposal to detect and recognise the hand gesture.
5. In the current version, the results are included in section 5 (Scheme of hand gesture recognition). I suggest that the results of the proposal be placed in a separate section to make them easier to find and read.
6. In the new results section, it is important that the authors provide as much information as possible about the experiments performed:

- How many samples did the authors take for each gesture evaluated?

- Do all the samples evaluated correspond to the same person?

- etc.

Author Response

Please see the attachement.

Author Response File: Author Response.docx

Reviewer 3 Report

Rich and extensive graphic material is used.

The manuscript is interesting in the field of acoustic devices development, information robotics, medicine, computer science and educational didactics.

Author Response

Thank you very much for reviewing our manuscript. We greatly appreicate your comments.

Round 2

Reviewer 1 Report

The paper is good enough to publish