An Experimental Study on the Charging Effects and Atomization Characteristics of a Two-Stage Induction-Type Electrostatic Spraying System for Aerial Plant Protection

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article is devoted to the study of a spraying system for plant protection using a UAV. The study is well planned, has scientific and practical interest, and corresponds to the subject matter of the journal "Agronomy".

To publish, authors must take into account the following comments:
1) At the beginning of the article, present a diagram of your research in the form of mind maps or a graphical abstract. This is useful for clarity of understanding by the reader.
2) Since the article is published in the journal "Agronomy", devote more paragraphs to the area of ​​application (gardens, fields, etc., where exactly it was tested, what effect for the agricultural enterprise). Emphasize the practical implications of the results obtained for real applications in plant protection using UAVs.
3) The keywords also need to be expanded on plant protection
4) At the end of section 1, formulate the research objective and tasks more clearly in the format 1,2,3…
5) The conclusions should also be consistent with the research objectives
6) Formulate more clearly how exactly the proposed two-stage system differs from existing single-stage induction or other types of electrostatic systems, especially in the context of UAVs. It would be good to include a short digression, since this topic is unfamiliar to many. Emphasize the unique advantages or characteristics of the proposed system
7) The discussion section should more actively compare the obtained results with the results of other published works, especially in the field of electrostatic spraying for UAVs.
8) The use of a laser droplet size analyzer (Malvern Spraytec) is mentioned. Provide more details about the device settings (measuring distance, sampling frequency, etc.) and how the measurements were carried out to obtain representative data.
9) What economic effect is expected from your study and how is it achieved?
10) Have your device been field tested? On what specific UAV models? It is necessary to write about this, provide real photos.
11) . The figures must be enlarged, many have unreadable text (Fig. 13, 14,15,18). Some figures must be combined under one number: 14 and 15, 20 and 21, 22 and 23)
12) Specify what software is shown in Fig. 14 and 15. Also check that the software used is indicated everywhere (statistical processing, diagrams, etc.)

Author Response

Main issue 1: At the beginning of the article, present a diagram of your research in the form of mind maps or a graphical abstract. This is useful for clarity of understanding by the reader.

Response 1: Thank you very much for your constructive suggestion. The proposal to include a mind map at the beginning of the article is indeed an excellent way to enhance readers' comprehension efficiency. We fully recognize the value of this visualization approach and will actively incorporate it in our future research papers. Regarding the current manuscript, we have dedicated substantial effort to ensure the textual logic and rigor as well as the narrative flow. The existing structural design and core results figures are intended to intuitively convey the research findings. Our current priority is to optimize the presentation of these core elements to their fullest potential. In response to your recommendation, we have meticulously refined the Introduction section. By providing a concise textual overview of the research framework and key components, we aim to achieve a similar guidance effect to that of a graphical abstract, enabling readers to clearly grasp the study's overarching structure.

 

Main issue 2: Since the article is published in the journal "Agronomy", devote more paragraphs to the area of application (gardens, fields, etc., where exactly it was tested, what effect for the agricultural enterprise). Emphasize the practical implications of the results obtained for real applications in plant protection using UAVs.

Response 2: Additional sections have been incorporated into the manuscript to elaborate on application domains such as orchards and farmlands. The practical implications of our research findings have been specifically highlighted, particularly regarding the employment of drones for crop protection in real-world agricultural practices. This technology holds broad application prospects in agricultural settings such as orchards and farmlands. It can significantly enhance the targeted deposition efficiency of pesticides, reduce drift losses and chemical usage, thereby enabling agricultural enterprises to achieve practical economic benefits including reduced operational costs, improved pest control efficacy, and minimized environmental pollution while generating environmental benefits.(lines 35-40)

 

Main issue 3: The keywords also need to be expanded on plant protection

Response 3: The keywords section has been expanded to include additional content related to "crop protection". Keywords: Plant protection; Plant protection UAV; Electrostatic spraying; Two-stage induction-type; Charging effect; Atomization characteristics (lines 41-42)

 

Main issue 4: At the end of section 1, formulate the research objective and tasks more clearly in the format 1,2,3…

Response 4: The research objectives and tasks have been clearly enumerated in a numbered list format (1., 2., 3., …) at the conclusion of Section 1. The specific research objectives and tasks primarily include: 1. Developing a two-stage inductive charging device to enhance the charge capacity of electrostatic spray droplets, achieving synergistic optimization of charging efficiency and atomization characteristics; 2. Quantitatively analyzing the interaction mechanisms of operational parameters (spray pressure, charging voltage, spray height) on droplet charge-to-mass ratio (q/m) and particle size distribution; 3. Establishing a response surface prediction model for charging efficacy and atomization performance to provide a theoretical basis for parameter optimization in plant protection UAV electrostatic spray systems.(lines 96-105)

Main issue 5: The conclusions should also be consistent with the research objectives

Response 5: The Conclusion section has been revised to ensure full alignment with the research objectives presented earlier in the manuscript.

Main issue 6: Formulate more clearly how exactly the proposed two-stage system differs from existing single-stage induction or other types of electrostatic systems, especially in the context of UAVs. It would be good to include a short digression, since this topic is unfamiliar to many. Emphasize the unique advantages or characteristics of the proposed system

Response 6: A concise explanation has been incorporated to explicitly delineate the distinctions between the proposed two-stage system and existing single-stage inductive or other types of electrostatic systems, highlighting the distinctive advantages and features of our approach. This two-stage structure differs significantly from single-stage inductive systems: the primary electrode focuses on pre-charging in the liquid film breakup zone to enhance initial charging efficiency, while the secondary electrode provides a spatial gradient electric field to compensate for charge decay and regulate droplet trajectories. This configuration overcomes the charging efficiency limitations of traditional systems in aerial plant protection operations and enhances resistance to wind field interference.(lines 114-120)

 

Main issue 7: The discussion section should more actively compare the obtained results with the results of other published works, especially in the field of electrostatic spraying for UAVs

Response 7: A brief comparison of our results with those reported in published literature has been included in the Discussion section. Experimental results demonstrate that compared with existing aviation electrostatic spray research,As exemplified by the 1.05 mC/kg charge-to-mass ratio achieved with the annular electrode developed by Wen Jianlong's team (at 12 kV) and the 42.3% drift reduction rate reported by Lian Qi et al. using planar electrodes , the dual-stage structure achieves enhanced charging efficiency through synergistic pre-charging and charge compensation effects. The device optimizes surface charge distribution on droplets, effectively suppressing charge escape phenomena and contributing to charge-to-mass ratio retention. Furthermore, it significantly improves the concentration uniformity of droplet size distribution within the core atomization zone. (lines 527-534)

 Main issue 8: The use of a laser droplet size analyzer (Malvern Spraytec) is mentioned. Provide more details about the device settings (measuring distance, sampling frequency, etc.) and how the measurements were carried out to obtain representative data.

Response 8: Details regarding instrument configuration (e.g., measurement distance, sampling frequency) and measurement procedures for obtaining statistically significant results have been added to the manuscript. The droplet size distribution test was completed at the Precision Application Technology Research Centre of China Agricultural University, using a laser diffraction-based method to build a fogging detection test bed (Figure 7). The core equipment of the system includes: (1) Malvern Spraytec real-time spray particle size analyser: equipped with a 300 mm focal length lens set, measuring range 0.1-2000 μm, sampling frequency of 2500 Hz, in line with the ISO 13320 standard;The measurement distance was fixed within the core atomization zone (0-200 mm below the nozzle), with 5 replicates collected per test condition (each lasting 2 s) to ensure statistical significance of the particle size distribution. (2) electrostatic spraying test bench: positioning accuracy of±1 mm, equipped with laser alignment system to ensure that the measurement of the optical path and the axis of the fog field coincide. Figure 8 shows the schematic diagram of the inductive electrostatic spray droplet size test system, using laser diffraction technology, can provide stable, real-time droplet size measurement data.(lines 198-210)

 Main issue 9: What economic effect is expected from your study and how is it achieved?

Response 9: To incorporate potential economic benefits arising from this study and outline pathways for their realization. From an economic benefit realization perspective, the reduction in drift miss rate directly decreases pesticide waste and potential compensation claims for phytotoxicity damage. The improvement in pesticide utilization rate means that comparable pest control efficacy can be achieved with reduced application volume per unit area, which saves farmers direct costs. The optimization of intelligent operational parameters enhances work efficiency and consistency while reducing additional costs incurred by ineffective results due to operational errors. The combined effect of these technical advantages is expected to significantly lower the overall costs of crop protection operations and increase the economic returns of pest control measures.(lines 548-556)

Main issue 10: Have your device been field tested? On what specific UAV models? It is necessary to write about this, provide real photos.

Response 10: This study primarily employed indoor experiments, utilizing hydraulic nozzles for plant protection drones as the test objects. Given that the research focused on laboratory static testing to control for outdoor environmental interference factors affecting the system, field trial components were not included. However, preliminary testing has been conducted on the DJI Agricultural T20 plant protection drone. Subsequent research will involve more detailed outdoor studies centered on this technology.

Main issue 11: The figures must be enlarged, many have unreadable text (Fig. 13, 14,15,18). Some figures must be combined under one number: 14 and 15, 20 and 21, 22 and 23)

Response 11: The figures have been optimized and standardized in terms of size and formatting (e.g., resolution, file types) to ensure enhanced clarity and visual consistency.

 

Main issue 12: Specify what software is shown in Fig. 14 and 15. Also check that the software used is indicated everywhere (statistical processing, diagrams, etc.)

Response 12: We have verified the relevant software standards used in this study. Figures 14 and 15 present results from the Design Expert experimental design and analysis software, through which models were fitted and analyzed based on experimental data. The optimal response values were determined using a controlled variable approach.

We would like to thank the referee again for taking the time to review our manuscript!

Reviewer 2 Report

Comments and Suggestions for Authors

This study developed a two-stage aerial electrostatic spraying device based on hydraulic atomization and electrostatic induction to address issues in plant protection UAV applications. The overall quality and scope of this manuscript is suitable for this journal. I recommend accept it after minor revision. Revision suggestion is as below:

Figure 14, and 15 are not clear. Please increase the resolution of these figures. Please also explain how did you determine on 1.79m as the critical height.

Lin 436-437 has formatting problems. Please revise. 

Author Response

Main issue 1: Figure 14, and 15 are not clear. Please increase the resolution of these figures. Please also explain how did you determine on 1.79m as the critical height.

Response 1: The image resolution in Figures 14 and 15 has been enhanced.With Y=0.8 mC/kg as the electrostatic spray charging effectiveness threshold, the parameter boundaries were inverted by a multiple quadratic regression model.In the case of the spray voltage and spray flow to achieve the best charging state, the spray height critical point of 1.79m, that is, in the spray height of not less than 1.79m within the scope of the droplet charge to basically meet the electrostatic spray droplet charge requirements. Therefore, the value of 1.79 m represents an operational boundary derived through inverse modeling under predefined technical constraints. Its primary significance lies in transforming the theoretical optimum solution into benchmark parameters for field-operable implementation.

Main issue 2: Lin 436-437 has formatting problems. Please revise.

Response 2: The formatting issues in Lines 436-437 have been corrected.

We would like to thank the referee again for taking the time to review our manuscript!

 

Reviewer 3 Report

Comments and Suggestions for Authors

The study addresses an emerging topic driven by the significant benefits of applying agrochemicals in crops using unmanned aerial systems.

However, significant improvements are required in the manuscript for potential publication in this Journal. Key issues include: the need for thorough English language editing (particularly unnecessary capitalization mid-sentence); careful adjustment of measurement units; proper citation of all figures within the text; along with other specific comments detailed in the attached material.

Finally, in the Discussion section, the authors should expand their analysis by incorporating and critically engaging with relevant studies from the literature to strengthen their arguments and contextualize their findings.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English language needs to be revised.

Author Response

Main issue 1: the need for thorough English language editing (particularly unnecessary capitalization mid-sentence); careful adjustment of measurement units; proper citation of all figures within the text; along with other specific comments detailed in the attached material.

Response 1: Revisions to the English editing have been implemented, including meticulous verification and standardization of all units of measurement. All numerical data in cited texts have been carefully cross-checked and amended; along with other specific comments detailed in the supplemental materials.

 

Main issue 2: Finally, in the Discussion section, the authors should expand their analysis by incorporating and critically engaging with relevant studies from the literature to strengthen their arguments and contextualize their findings.

Response 2: The Discussion section has been expanded through critical integration of relevant studies from the literature, strengthening our arguments through comparative analysis relative to existing literature and reinforcing the novelty of our findings. This study innovatively designed a two-stage induction charging device to systematically analyze the interaction mechanisms among charging voltage, spray pressure, and height on droplet charge-to-mass ratio and particle size distribution. Experimental results demonstrate that compared with existing aviation electrostatic spray research,As exemplified by the 1.05 mC/kg charge-to-mass ratio achieved with the annular electrode developed by Wen Jianlong's team (at 12 kV) and the 42.3% drift reduction rate reported by Lian Qi et al. using planar electrodes , the dual-stage structure achieves enhanced charging efficiency through synergistic pre-charging and charge compensation effects. The device optimizes surface charge distribution on droplets, effectively suppressing charge escape phenomena and contributing to charge-to-mass ratio retention. Furthermore, it significantly improves the concentration uniformity of droplet size distribution within the core atomization zone. These findings validate the effectiveness of the two-stage induction structure in overcoming the charge saturation threshold inherent to conventional electrostatic spraying systems.

We would like to thank the referee again for taking the time to review our manuscript!

Reviewer 4 Report

Comments and Suggestions for Authors

While the paper refers to ''... Two-stage Induction-Type Electrostatic Spraying System for Aerial Plant Protection '', the content and experiments deal only with analysis of a newly designed '' two inductive charging device ''. Also, the author acknowledges that laboratory experiments have their limitations (lines 520-522), but the main issue is that these experiments were not even close with the requirements for  laboratory simulation of the developed device and its use for UAV's. The paper might have a very good background, innovation, methodology, and results if the author analyses only the developed device and its characteristics or the laboratory experiments should be properly developed in order to prove that the designed device is (or might be) suitable for aerial application of plant protection products.

Author Response

Main issue : While the paper refers to ''... Two-stage Induction-Type Electrostatic Spraying System for Aerial Plant Protection '', the content and experiments deal only with analysis of a newly designed '' two inductive charging device ''. Also, the author acknowledges that laboratory experiments have their limitations (lines 520-522), but the main issue is that these experiments were not even close with the requirements for  laboratory simulation of the developed device and its use for UAV's. The paper might have a very good background, innovation, methodology, and results if the author analyses only the developed device and its characteristics or the laboratory experiments should be properly developed in order to prove that the designed device is (or might be) suitable for aerial application of plant protection products.

Response : This study primarily employed indoor experimental methodology, utilizing hydraulic nozzles from plant protection drones as the test subjects. Given its focus on laboratory static testing to control for outdoor environmental interference factors affecting the system—representing fundamental applied research for this aerial electrostatic spraying system—field trial components were deliberately excluded. However, preliminary validation has been conducted on DJI Agricultural series plant protection drones. Subsequent research will involve comprehensive outdoor validation trials to further evaluate this technology. We sincerely appreciate the reviewers' constructive feedback. In subsequent research phases, we will conduct more rigorous laboratory simulations replicating authentic drone operational conditions and implement comprehensive field validation trials.

We would like to thank the referee again for taking the time to review our manuscript!

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This version of the article improves the previous one, the authors responded to most of the comments and made adjustments to the article.
In particular, the list of tasks was formulated and the conclusions were brought into line, paragraphs on the practical application of the development in agronomy were added, the list of keywords was expanded, the advantage of a two-stage structure was added, the discussion section was expanded, the description of the laser droplet size analyzer was expanded, the economic effect was indicated, some figures were improved for better readability of the text.

Comments on the new version of the article:
1) I would still recommend making a research scheme in the form of a graphic annotation at the beginning of the article
2) In the answers, you indicated the Design Expert software, check that this name and the names of other equipment (including the UAV model) are in the text of the article
3) The text in the figures with graphs, in the opinion of the reviewer, is not yet large enough for visual perception. It is necessary to enlarge the figures themselves, then the text will increase, or enlarge the text in the figures. The text should be commensurate with the main text of the article

Author Response

Main issue 1: I would still recommend making a research scheme in the form of a graphic annotation at the beginning of the article

Response 1: The research technical roadmap has been presented graphically at the beginning of the article along with an explanation of the research plan.

Main issue 2: In the answers, you indicated the Design Expert software, check that this name and the names of other equipment (including the UAV model) are in the text of the article

Response 2: It has been confirmed that the designation "Design-Expert software" along with all other equipment nomenclature are consistently referenced throughout the manuscript.

Main issue 3: The text in the figures with graphs, in the opinion of the reviewer, is not yet large enough for visual perception. It is necessary to enlarge the figures themselves, then the text will increase, or enlarge the text in the figures. The text should be commensurate with the main text of the article.

Response 3: The image clarity has been optimized by overall scaling up the figures, thus proportionally increasing the text size.

We would like to thank the referee again for taking the time to review our manuscript!

Reviewer 3 Report

Comments and Suggestions for Authors

Many suggestions were made in the first version, which were not incorporated into this new version. Therefore, attached is the first version with all my comments.

Comments for author File: Comments.pdf

Author Response

Main issue : Many suggestions were made in the first version, which were not incorporated into this new version. Therefore, attached is the first version with all my comments.

Response : The suggestions proposed in the first version have been carefully revised and incorporated into this new version.

We would like to thank the referee again for taking the time to review our manuscript!

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This paper analyses a novel developed two-stage aerial electrostatic spraying device in order to solve issues related to plant protection application techniques, the quality of the treatment and environmental pollution (e.g. broad droplet size spectrum, spray drift). The newly developed device is meant to be used in UAV applications of plant protection products, the experiments being carried out in laboratory restrictive conditions using several key working parameters, such as particle size distribution, liquid pressure, charging voltage, droplet charge to mass ratio, and spray height.

The paper accurately describes the issues related to UAV applications of plant protection products, highlighting that for the required working UAV parameters, the droplets are susceptible to drift and off-target deposition. In order to solve this problem, the paper identifies the need for deposition enhancement techniques, such as electrostatic spraying devices designed in order to be suitable for aerial application of pesticides.

In order to solve the identified bottlenecks, the research objectives are accurately defined to properly characterize the newly developed inductive charging device, to analyze the interaction mechanisms of accurate operational parameters and to provide a theoretical basis for parameter optimization in plant protection UAV electrostatic spray systems.

The paper acknowledges that laboratory experiments have their limitations (lines 520-522), but the main issue is that these experiments were not in line with the minimum requirements for laboratory simulation of the developed device for aerial plant protection. However, the paper has a very good background, innovation, methodology, and results, so the paper analyses only the developed device and its characteristics, proving that the two-stage induction device can effectively break through the charge saturation threshold of traditional electrostatic spraying, which provides a theoretical basis and technical support for the optimal design of electrostatic spraying system for plant protection.

The laboratory experiments can be further developed in order to prove that the designed device is (or might be) suitable for aerial application of plant protection products, in order to find its strengths and weaknesses in real-world scenarios.

Author Response

Comments and Suggestions for Authors : This paper analyses a novel developed two-stage aerial electrostatic spraying device in order to solve issues related to plant protection application techniques, the quality of the treatment and environmental pollution (e.g. broad droplet size spectrum, spray drift). The newly developed device is meant to be used in UAV applications of plant protection products, the experiments being carried out in laboratory restrictive conditions using several key working parameters, such as particle size distribution, liquid pressure, charging voltage, droplet charge to mass ratio, and spray height.

The paper accurately describes the issues related to UAV applications of plant protection products, highlighting that for the required working UAV parameters, the droplets are susceptible to drift and off-target deposition. In order to solve this problem, the paper identifies the need for deposition enhancement techniques, such as electrostatic spraying devices designed in order to be suitable for aerial application of pesticides.

In order to solve the identified bottlenecks, the research objectives are accurately defined to properly characterize the newly developed inductive charging device, to analyze the interaction mechanisms of accurate operational parameters and to provide a theoretical basis for parameter optimization in plant protection UAV electrostatic spray systems.

The paper acknowledges that laboratory experiments have their limitations (lines 520-522), but the main issue is that these experiments were not in line with the minimum requirements for laboratory simulation of the developed device for aerial plant protection. However, the paper has a very good background, innovation, methodology, and results, so the paper analyses only the developed device and its characteristics, proving that the two-stage induction device can effectively break through the charge saturation threshold of traditional electrostatic spraying, which provides a theoretical basis and technical support for the optimal design of electrostatic spraying system for plant protection.

 

The laboratory experiments can be further developed in order to prove that the designed device is (or might be) suitable for aerial application of plant protection products, in order to find its strengths and weaknesses in real-world scenarios.

Response : In the future, we will strive to develop laboratory experiments to more comprehensively demonstrate the suitability of the designed equipment for the aerial application of plant protection products, ultimately identifying its strengths and weaknesses in real-world settings.

We sincerely appreciate the reviewers for their valuable suggestions and positive feedback!

Author Response File: Author Response.pdf