Powering Underwater Robotics Sensor Networks Through Ocean Energy Harvesting and Wireless Power Transfer Methods: Systematic Review
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis is an excellent contribution and I strongly recommend publication. It provides "one-stop shopping" on important topics related to how IoUT devices can be powered. the authors' treatment of these topics is technically sound and clearly expressed.
I have only one criticism: they mention ultrasonic power transfer and they include a reference, [30] Ghaffarivardavagh. But I do not see any corresponding citation in the body of the paper, so this reference is not connected to any discussion. A more appropriate reference would be:
https://www.nature.com/articles/s41467-022-33223-x
Frankly, I find the premise of the Afzal paper to be outlandish. But it was published in Nature so I would really like to see the authors discuss that work in the context of the larger summary of methods they provide.
Author Response
Response to Reviewer 1 Comments
We would like to thank Reviewer 1 for the good and constructive comments on the manuscript.
Comments 1: I have only one criticism: they mention ultrasonic power transfer and they include a reference, [30] Ghaffarivardavagh. But I do not see any corresponding citation in the body of the paper, so this reference is not connected to any discussion. A more appropriate reference would be:
https://www.nature.com/articles/s41467-022-33223-x
Frankly, I find the premise of the Afzal paper to be outlandish. But it was published in Nature so I would really like to see the authors discuss that work in the context of the larger summary of methods they provide.
Response 1: We would like to thank Reviewer 1 for this constructive comment on the manuscript. We agree that the Nature article is a more appropriate and relevant reference for our review. Accordingly, we have incorporated the Afzal paper (now reference [77]) into the text on page 20, line 493, and included its values in Table 7 (page 21, line 519) for comparison.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe Authors have presented a review on powering underwater robotics sensor networks through ocean energy harvesting and wireless power transfer methods. They investigated recent advancements in powering various devices in underwater robotic sensor networks, focusing on two main approaches: ocean energy harvesting and wireless power transfer.
Overall, the manuscript constitutes a valuable resource for readers searching for a general overview of the subject matter. Unfortunately, the scientific quality across the sections varies considerably.
While the Section 4 devoted to Wireless Power Transfer is generally well written, the theoretical introduction of each subsection is, in my view, excessively long and unnecessarily detailed. The fundamental principles of the individual energy transfer methods are already well documented in the basic literature, and reiterating widely known physical phenomena adds little value to this review. This overextended introduction detracts from the conciseness and focus expected in a state-of-the-art survey. In contrast, the summary tables presenting the reviewed solutions are indeed informative and well prepared. Nevertheless, the review would be significantly strengthened if it also included at least approximate or indicative cost estimates for implementing a power supply method, which are currently entirely absent.
The review of ocean energy harvesting methods presented in Section 3 performs considerably worse. It is prepared at a very high level of generality and does not contribute anything of real interest to the subject matter. The authors describe various energy harvesting methods, but provide no data—such as installation costs, generated power, efficiency factors, or other cost-related indicators—that would enable their comparison or assessment of their suitability for powering AUVs or sensor networks. There is also no information on whether such energy can be practically and easily used in small or large AUVs. Furthermore, the authors mix systems designed for connection to the electrical grid with systems that could be used to power a single sensor network node or an AUV. For example, in Section 3.3 they almost exclusively consider kinetic energy of water sources intended for industrial-scale networks, whereas in Section 3.4 they mention the possibility of using Ocean Thermal Energy Conversion for AUVs but provide no parameters of such a solution, making it impossible to assess its usefulness in comparison to other energy sources. The review style in Section 3 should be brought in line with the more focused and informative approach demonstrated in Section 4.
The adopted concept of the introduction, spread across Sections 1 and 2, is highly problematic and lacks clarity.
- The same information is redundantly repeated across multiple subsections, which creates unnecessary verbosity and undermines the manuscript’s conciseness.
- The inclusion of Table 1 appears unjustified. It is not referenced in the substantive part of the review, and the majority of the cited publications bear little or no direct relevance to the core subject matter.
- The rationale for isolating Subsection 1.2 is unclear, as it contributes no new insights to the discussion. Moreover, the omission of publications [23] and [24] from Table 1 is inconsistent, especially given that the table already contains review articles addressing both powering underwater devices and data transfer for underwater solutions (e.g., [15]).
- The introduction of SWIPT and SLIPT definitions in Subsection 1.2 is unjustified, as these terms are never used or discussed in the remainder of the manuscript.
- Publication [24] is misclassified—it is not a review but a standard research article.
- Subsection 2.3 deviates substantially from the declared scope of the review. The review was explicitly defined as focusing on two primary approaches: ocean energy harvesting (OEH) and wireless power transfer (WPT). While the topics of battery power and, in particular, nuclear energy are interesting, they are entirely outside the stated scope. Furthermore, the discussion provided does not extend beyond a superficial popular-science description and falls far short of the analytical depth expected of a literature review in a serious scientific journal.
- Subsection 2.4 suffers from the same issue of being outside the agreed scope. The topic mentioned is indeed of interest, but it is addressed only superficially and is never developed in later sections of the manuscript. The content reads as a popular-science aside and fails to provide any substantive contribution to the review.
Author Response
Response to Reviewer 2 Comments
We thank Reviewer 2 for a thorough, constructive and helpful review.
Comment 1: The review would be significantly strengthened if it also included at least approximate or indicative cost estimates for implementing a power supply method, which are currently entirely absent.
Response 1: We agree that cost considerations are an important aspect, even though they fall outside the scope of the present manuscript. To acknowledge this, we have added two clarifications in Chapter 5 (Discussion and Conclusions). First, at lines 631–633, we now state: “When assessing technological efficiency further, it will also require consideration of both installation and operational costs. While such cost analyses are critical for determining the most suitable solution for specific projects, they are beyond the scope of this article.” Second, at line 640, we added: “This also presents an opportunity to examine cost estimates for the different solutions and how cost affects power efficiency.”
Comment 2: The authors describe various energy harvesting methods, but provide no data—such as installation costs, generated power, efficiency factors, or other cost-related indicators—that would enable their comparison or assessment of their suitability for powering AUVs or sensor networks.
….
The review style in Section 3 should be brought in line with the more focused and informative approach demonstrated in Section 4.
Response 2: We thank Reviewer 2 for this helpful suggestion. To strengthen Section 3, we have added a new table (Table 4, introduced at line 378) that summarizes the literature studies and provides indicative power levels reported for the various OEH techniques. Corresponding text has been added at lines 357–359: “Table 4 also gives an overview of the OEH techniques, indicating the expected power levels reported in the literature.” Additionally, we clarified the limitations of tidal range energy at line 257 by adding: “…thus less suitable for smaller-scale and mobile IoUT applications.”
Below we answer the numerical concerns point by point:
Comments 3: 1. The same information is redundantly repeated across multiple subsections, which creates unnecessary verbosity and undermines the manuscript’s conciseness.
Response 3: Thank you for this comment. Ensuring clarity and conciseness is a key priority for us. Some of the responses to the following comments below involve removing text from the manuscript, and by doing so, the accumulated deleted text is approximately two pages of the manuscript across several subsections. We believe that by doing so, the manuscript has become more concise and readable.
Comments 4: 2. The inclusion of Table 1 appears unjustified. It is not referenced in the substantive part of the review, and the majority of the cited publications bear little or no direct relevance to the core subject matter.
Response 4: Thank you for this fair point, and we agree to it. Table 1 has been removed from the manuscript, along with references to it in the text.
Comments 5: 3. The rationale for isolating Subsection 1.2 is unclear, as it contributes no new insights to the discussion. Moreover, the omission of publications [23] and [24] from Table 1 is inconsistent, especially given that the table already contains review articles addressing both powering underwater devices and data transfer for underwater solutions (e.g., [15]).
Response 5: We value this point as we strive to have the article focused and clear. Therefore, this subsection has been taken out of the manuscript to streamline the introduction and avoid inconsistencies.
Comments 6: 4. The introduction of SWIPT and SLIPT definitions in Subsection 1.2 is unjustified, as these terms are never used or discussed in the remainder of the manuscript.
Response 6: We thank the reviewer for pointing this out, it is an even stronger justification to take subsection 1.2 out of the manuscript, as has been done now and mentioned in our previous response (see Response 5).
Comments 7: 5. Publication [24] is misclassified—it is not a review but a standard research article.
Response 7: We thank the reviewer for highlighting this misclassification. Since Subsection 1.2 has now been removed, this misclassification no longer applies.
Comments 8: 6. Subsection 2.3 deviates substantially from the declared scope of the review. The review was explicitly defined as focusing on two primary approaches: ocean energy harvesting (OEH) and wireless power transfer (WPT). While the topics of battery power and, in particular, nuclear energy are interesting, they are entirely outside the stated scope. Furthermore, the discussion provided does not extend beyond a superficial popular-science description and falls far short of the analytical depth expected of a literature review in a serious scientific journal.
Response 8: This is a good point, and we agree with the comment. Therefore, we have taken the explanatory text regarding the nuclear power battery out, and just pointed out the fact that it falls outside the declared scope, as mentioned the comment.
Comments 9: 7. Subsection 2.4 suffers from the same issue of being outside the agreed scope. The topic mentioned is indeed of interest, but it is addressed only superficially and is never developed in later sections of the manuscript. The content reads as a popular-science aside and fails to provide any substantive contribution to the review.
Response 9: We thank the reviewer for this comment. To keep the review focused and within scope, we have removed Subsection 2.4 totally out of the manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsThis manuscript presents a review of underwater powering solutions for the Internet of Underwater Things (IoUT), with a particular focus on Ocean Energy Harvesting (OEH) and Wireless Power Transfer (WPT) technologies. It provides a comprehensive analysis of various research works, highlighting both their strengths and limitations. Overall, the paper successfully compiles a wide range of relevant studies and offers valuable insights into the current state of the field.
Please check and address the following revision points and comments regarding the paper.
1. In line 322, for the numerical value “2.5” mentioned in the text, it is recommended to use the unit symbol “W” instead of spelling out “watt.”
2. It appears that a space should be inserted between numerical values and units in both the main text and tables. A thorough consistency check is recommended throughout the manuscript.
3. In line 429, Figure 13 appears to be placed on a new line. If there is no specific reason for this, it should be adjusted. (No response is required.)
4. Some abbreviations are spelled out multiple times, for example, “Wireless Power Transfer (WPT)” appears in full more than once. The full term should be given only at its first mention. Please check OEH and other abbreviations throughout the text for consistency.
5. In Table 4, under the “Technique” column, please verify the layout. It seems that some cells should be merged.
6.Please provide the authors’ perspective on Electric Resonance Coupling in WPT. There is a substantial amount of research on electric-field-based WPT for underwater applications, yet this review does not address it. Please explain why it was excluded.
Author Response
Response to Reviewer 3 Comments
We would like to thank Reviewer 3 for the good and constructive comments on the manuscript.
Comments 1: In line 322, for the numerical value “2.5” mentioned in the text, it is recommended to use the unit symbol “W” instead of spelling out “watt.”
Response 1: Thank you for noticing this. We corrected “watt” to “W” (now line 317) and also changed “50 meters” to “50 m” at line 239 for consistency.
Comments 2: It appears that a space should be inserted between numerical values and units in both the main text and tables. A thorough consistency check is recommended throughout the manuscript.
Response 2: This is a good reminder to improve the quality of the article. After a thorough review of the manuscript, some instances were corrected. There were four instances of Temperature (°C) values in table 1, two cases in line 273, and one in line 279, also on temperature values (°C), and the “GAP distance” in table 10 had four instances.
Comments 3: In line 429, Figure 13 appears to be placed on a new line. If there is no specific reason for this, it should be adjusted. (No response is required.)
Response 3: Thank you for noticing this formatting issue. The figure has been adjusted accordingly.
Comments 4: Some abbreviations are spelled out multiple times, for example, “Wireless Power Transfer (WPT)” appears in full more than once. The full term should be given only at its first mention. Please check OEH and other abbreviations throughout the text for consistency.
Response 4: We thank the reviewer for highlighting this. We revised the use of full terms and abbreviations to ensure consistency. For example: AC (line 492), AUV (lines 124, 216, 283, 433, 624), IoUT (line 306), OEH (lines 118, 150, 154, 364, 375), OTEC (line 351), MFC (line 315 and Table 3), PMS (Table 3), PZT (lines 468, 484, 488), and WPT (lines 62, 120, 150, 161, 428, 438, 479, 495, 497, 503, 513, 525, 564, 604, 607, 609, 651, and in Tables 1 and 9).
Comments 5: In Table 4, under the “Technique” column, please verify the layout. It seems that some cells should be merged.
Response 5: This is a good point. Now the format of the table has been changed following the table layout of the journal.
Comments 6: Please provide the authors’ perspective on Electric Resonance Coupling in WPT. There is a substantial amount of research on electric-field-based WPT for underwater applications, yet this review does not address it. Please explain why it was excluded.
Response 6: We thank the reviewer for this valuable suggestion, which improves the completeness of our review. We have now added the following discussion of electric-field (capacitive) resonant coupling starting at line 176:
Electric-field (capacitive) resonant coupling has been investigated for wireless power transfer (WPT), but it is not considered suitable for underwater applications—particularly in seawater. The high conductivity of the medium leads to substantial energy losses, making power transfer inefficient. In contrast, magnetic (inductive or resonant) coupling is far more tolerant in this environment. Moreover, the small coupling capacitance achievable underwater necessitates very high plate voltages to deliver useful power, which increases insulation requirements and introduces safety concerns near instruments and personnel. Multiple reviews of underwater WPT consistently highlight these limitations and recommend magnetic approaches as the preferred solution for underwater charging [18,28,29].
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsAs I have written previously, the Authors have presented an interesting and valuable study on powering underwater robotics sensor networks through ocean energy harvesting and wireless power transfer methods.
I have carefully studied the Authors’ response to my earlier comments. The Authors have significantly improved the manuscript and highlighted changes. They have addressed the majority of the remarks to a satisfactory extent, which has enhanced the clarity and overall quality of the paper.
In its current form, I believe that the manuscript meets the editorial requirements of the Journal. The structure of the paper is clear, the figures and tables are informative, and the conclusions are supported by the presented results.
Therefore, I am of the opinion that the paper can be accepted for publication, pending standard proofreading by the Editorial Board to ensure linguistic accuracy and editorial consistency.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have provided detailed responses to the reviewers’ comments and have made appropriate revisions to the manuscript.
