Reliability Analysis of Coating Material on Polyvinylidene Fluoride Layers Used in Piezoelectric Vibration Energy Harvesting Device

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, a multilayer piezoelectric oscillation energy harvesting device was made by means of simple bonding, and the resistance and capacitance changes before and after aging were compared to evaluate the reliability of PVDF coating materials. The experimental process is simple, but the subject is relatively lacking in features and highlights.

  

1. There are some symbolic errors in this paper，for example, in the description of temperature cycle range in 2.2, the symbol of Celsius should be "℃". Most of the abbreviations for number should be "No.";

2. Some charts are incorrectly labeled，for example figure.1 and figure.2;

3. The semantics of some statements are unclear，for example, “In the layers where the resistance is not measured……”in 4.discuss，it is suggested that the author modify this part;

4. Some contents lack theoretical suppor , for example, “For these reasons, the piezoelectric PVDF film has partially or completely lost its electrical connection to the surface electrodes.” and “the partial detachment of the piezoelectric PVDF film from the core is visually evident due to cyclical effects and air voids between the PVDF film and the surface of the core during bonding ”. in 3.1 ;the rise in surface resistivity is attributed to the degradation of the PVDF film, cracks and visible surface corrosion, in 3.2 .It is suggested to modify and add the theoretical basis;

5. The discussion of the results in this paper is limited to the surface of the data. For example, the conclusions of capacitor decline and resistance rise in 3.1 and 3.2 are simply attributed to the damage of PVDF film, without in-depth mechanism exploration.It is suggested that the author analyze the reason of its performance change from the mechanism

6. The purpose of this work is to analyze the reliability of PVDF coating material in piezoelectric energy harvesting device. However, variables are not controlled in the experiment process, nor is it compared with other referable standards, so it is impossible to see whether the material has reliability directly.It is suggested that the author introduce some application scenarios to evaluate or compare with other similar work in the conclusion.

Comments on the Quality of English Language

English writting is OK.

Author Response

Response to Reviewer 1Comments

 

Point 1: . There are some symbolic errors in this paper, for example, in the description of temperature cycle range in 2.2, the symbol of Celsius should be "℃". Most of the abbreviations for number should be "No.";

Response 1: Authors are grateful to the reviewer for the feedback and encouraging comment. Corrections are made as suggested.

Point 2: Some charts are incorrectly labeled，for example figure.1 and figure.2;

Response 2: Labels are revised.

 

Point 3: The semantics of some statements are unclear，for example, “In the layers where the resistance is not measured……”in 4.discuss，it is suggested that the author modify this part;

Response 3: The sentence mentioned is modified according to context.

Point 4:  Some contents lack theoretical support , for example, “For these reasons, the piezoelectric PVDF film has partially or completely lost its electrical connection to the surface electrodes.” and “the partial detachment of the piezoelectric PVDF film from the core is visually evident due to cyclical effects and air voids between the PVDF film and the surface of the core during bonding ”. in 3.1 ;the rise in surface resistivity is attributed to the degradation of the PVDF film, cracks and visible surface corrosion, in 3.2 .It is suggested to modify and add the theoretical basis;

Response 4: More information is added in introduction and discussion section to elaborate on the

theretical basis for the results obtained. A new paragraph is added in the introduction section to elaborate on this point. The link betweeen electrical power and durability can be explained through the following theoretical principles:

• Piezoelectric Properties: PVDF is a piezoelectric material, which means it generates an electric charge when subjected to mechanical stress. However, this property also makes it sensitive to mechanical stress. Repeated mechanical deformation can cause material fatigue and lead to structural defects, such as the crumpling and peeling of the film[6], [17].
• Thermal Expansion and Stress: When materials experience cyclic thermal stresses, their coefficient of thermal expansion comes into play. PVDF, like many other materials, expands and contracts with changes in temperature. This can create mechanical stress at the interfaces and within the material itself. Cyclic thermal stresses can induce mechanical strain, leading to delamination or peeling of the film due to the differential expansion and contraction between layers as seen in references [13], [18].
• Electrical Connection Loss: When cracks, corrosion, or chipping occur on the surface of the PVDF film, the electrical connection to the surface electrodes can be compromised. This is due to both physical separation and the potential for increased electrical resistance at these damaged points [19], [20]. In a piezoelectric energy harvester, a continuous and reliable electrical connection is crucial for efficient energy conversion

 

Point 5: The discussion of the results in this paper is limited to the surface of the data. For example, the conclusions of capacitor decline and resistance rise in 3.1 and 3.2 are simply attributed to the damage of PVDF film, without in-depth mechanism exploration.It is suggested that the author analyze the reason of its performance change from the mechanism

Response 5: Additional data is added like the standard deviation fo the surface resistance of the four samples and the generated output voltage data of  the six harvester samples in section 2.3.1 and 3.1 .

 

Point 6: The purpose of this work is to analyze the reliability of PVDF coating material in piezoelectric energy harvesting device. However, variables are not controlled in the experiment process, nor is it compared with other referable standards, so it is impossible to see whether the material has reliability directly.It is suggested that the author introduce some application scenarios to evaluate or compare with other similar work in the conclusion.

Response 6: The approach used in this study to measure the quality of the metal coating is new, there is limited existing literature for reference. However, the method used has enhanced our understanding of the subject matter, it has provided us with a simplified technique to know the condition of the metal coatiung after long hours of operation . sHowever, in discussion and conclusion section the application scenarios are suggested, the implications of these variations in reliability assesment is stressed upon and proved techniques are suggested to overcome these variations. The study suggests  spraying a protective coating on the PVDF film, using an intermediate plastic sheet between the core and the electrodes to prevent the metallization of the PVDF film from wearing away the edge of the electrodes during the flexing of the core of the piezoelectric oscillator. In future works a simulated model of the thermocycling process will be presented.   

 

 

English proofreading is done and revisions are made

Reviewer 2 Report

Comments and Suggestions for Authors

Reliability analysis of coating material on PVDF layers used…

 

Abstract

 

An abstract well written can be the difference between reading and not reading your manuscript…pay attention, please…

Is the thermocycling process used in this research? How to take advantage of its use?

Line 13. Usually in scientific texts, “room temperature” is better than “ambient temperature”

There are no numerical results. What are the differences before and after of aging process between aluminum and Copper-nickel coating materials on PVDF?

What is the suitability achieved in this study?

Line 21 Please check the English redaction and grammar…for improvement? “for improving” is better or also “to improve” the PVDF

What is the conclusion about the metal on PVDF coating suitability?

Authors must improve the Abstract because you don´t highlight the relevance or importance of the research and results…

Introduction

Authors can improve writing by being more concise or punctual, for example:

Lines 31-33 can be re-written like that: “Besides of sources such as sun or water to obtain renewable energy the mechanical vibrations are excellent sources [1]-[5]”

Line 37. When you speak about of efficiency of piezoelectric power…What is the link to the durability of the device?

Line 49-52. PVDF is already defined in the Abstract; besides these lines are equal to lines 16-18…

Line 70 If the results of variation in capacitance and resistance determine the quality of the metal coating on PVDF, then:

Discussion

1. Why does section four (discussion) has not any references to compare results with other devices,

research, etc.?

2. How can you demonstrate that results are unpublished and original?

3. How can you demonstrate that results are better than others?

4. How can know if the quality of the metal coating on PVDF is improving the harvest compared with other devices, experiments, and/or sources of energy?

Authors must improve considerably and substantially in the abstract, Introduction, Discussion, the English redaction to read this research better.

I did not include the comments concerning sections 2 and 3 in this review until you have improved the English redaction.

For these reasons, I can not recommend publishing the manuscript right now…

Comments on the Quality of English Language

See comments and suggestions in blue. These are only examples to improve the English redaction

Author Response

Response to Reviewer 2 Comments

 

Point 1: Is the thermocycling process used in this research? How to take advantage of its use?

Response 1: Authors are grateful to the reviewer for the positive and encouraging comment. The analysis of temperature and mechanical effects on piezoelectric oscillators has led to improvement of durability of piezoelectric oscillators:The study suggests  spraying a protective coating on the PVDF film, using an intermediate plastic sheet between the core and the electrodes to prevent the metallization of the PVDF film from wearing away the edge of the electrodes during the flexing of the core of the piezoelectric oscillator. In future works a simulated model of the thermocycling process will be presented.   

 

Point 2: Usually in scientific texts, “room temperature” is better than “ambient temperature”

Response 2: ambient tempearture is changed to room tempearture in all places

Point 3: There are no numerical results. What are the differences before and after of aging process between aluminum and Copper-nickel coating materials on PVDF?

Response 3: There is some numerical data to compare the surface resistance vales of Copper-nickel coatings and aluminium coatings. It is found that copper -nickel is more suitable for longetivity and higher tmeperatur applications.

Point 4:  Authors must improve the Abstract because you don´t highlight the relevance or importance of the research and results

Response 4: Abstract is revised. Efforts are made to describe in detail the methodology and data collection process to show that the research is based on an innovative approach to measure the quality of the metal coating on PVDF films that hasn't been used before.

Point 5: Lines 31-33 can be re-written like that: “Besides of sources such as sun or water to obtain renewable energy the mechanical vibrations are excellent sources [1]-[5]”

Response 5: Correction is made.

 

Point 6: When you speak about of efficiency of piezoelectric power…What is the link to the durability of the device?

Response 6: A new paragraph is added in the introduction section to elaborate on this point. The link betweeen electrical power and durability can be explained through the following theoretical principles:

• Piezoelectric Properties: PVDF is a piezoelectric material, which means it generates an electric charge when subjected to mechanical stress. However, this property also makes it sensitive to mechanical stress. Repeated mechanical deformation can cause material fatigue and lead to structural defects, such as the crumpling and peeling of the film[6], [17].
• Thermal Expansion and Stress: When materials experience cyclic thermal stresses, their coefficient of thermal expansion comes into play. PVDF, like many other materials, expands and contracts with changes in temperature. This can create mechanical stress at the interfaces and within the material itself. Cyclic thermal stresses can induce mechanical strain, leading to delamination or peeling of the film due to the differential expansion and contraction between layers as seen in references [13], [18].
• Electrical Connection Loss: When cracks, corrosion, or chipping occur on the surface of the PVDF film, the electrical connection to the surface electrodes can be compromised. This is due to both physical separation and the potential for increased electrical resistance at these damaged points [19], [20]. In a piezoelectric energy harvester, a continuous and reliable electrical connection is crucial for efficient energy conversion

 

 

Point 7: Line 49-52. PVDF is already defined in the Abstract; besides these lines are equal to lines 16-18…

Response 7:Corrections made, the above points are removed from introduction.

 

Point 8. Why does section four (discussion) has not any references to compare results with other devices, research, etc.?How can you demonstrate that results are unpublished and original?

 

Response 8: The approach used in this study to measure the quality of the metal coating is new, there is limited existing literature for reference. However, the method used has enhanced our understanding of the subject matter, it has provided us with a simplified technique to know the condition of the metal coatiung after long hours of operation . This has highlighted the originality of this work. In this case, the Discussion section might not include references for comparisons because there's little or no prior work directly related to this research.

 

Point 9. Authors must improve considerably and substantially in the abstract, Introduction, Discussion, the English redaction to read this research better

Response 9: Suggestion is considered and changes are implemented highlight and justify the reason to conduct this study and to demonstrate the originality of this  research through clear statements in the Introduction, detailed methodology, and the implications discussed in the Discussion.

 

All minor comments were considered and changed accordingly,  including relevant references from the MDPl. English proofreading is done and revisions are made

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is hard to follow: I simply didn't understand the core findings based on the experiments performed. Unless the flaws are addressed adequately, manuscript should not be accepted in this journal. My concerns are the following:

1. The authors organizes the manuscript in a particular order, which was very difficult to understand. They mentioned the theory of piezoelectricity and cantilever based energy generators, but it was never really described anywhere in the paper. For understanding, a proper introduction is necessary. Unfortunately its only vague. 

2. The sufficient motivation to carry out the experiments is missing. Why aging tests are required, how to improve the output and most importantly, discussions on electrical output are either missing or only casually presented. 

3. Weird mix up of future tense in 'Structure of the energy harvester and experimental design' section. Plenty of experiments were simply followed bizarre 'shall be' forms , which is unscientific. Experiments should be described either in simple past or present tense.

4. References are incomplete and not related to article, in most cases. See the following manuscript for a correct representation and studies associated to NGs and characterization and cite properly: Materials Horizons 9 (5), 1468-1478, 2022 and Journal of magnetism and magnetic materials 372, 214-223, 2014. 

5. There is no graphical presentation of any scientific data presentations: everything was presented in tables. For resistivity and capacitance studies, the proper curves are missing. There were other electric properties that considered more important to generators, such as current and voltage. They are also missing. Despite, the authors claimed that they claim, "Experimental studies have shown that energy harvesters with a PET core and a 270 PVDF film coated with a copper-nickel coating generate ~3.5 times higher output voltage 271 than those with a steel core and an aluminum-coated PVDF film". Where is the voltage plot?

Overall, the manuscript needs thorough overhaul, it appears more like a report than a scientific article. If the authors address each points carefully, i will gladly reconsider my decision of rejection. 

 

Comments on the Quality of English Language

English check is required. Tense is confusing all over the manuscript. 

Author Response

Response to Reviewer 3 Comments

 

Point 1: The authors organizes the manuscript in a particular order, which was very difficult to understand. They mentioned the theory of piezoelectricity and cantilever based energy generators, but it was never really described anywhere in the paper. For understanding, a proper introduction is necessary. Unfortunately its only vague. 

Response 1: Authors are grateful to the reviewer for the feedback and encouraging comment. Changes are made to make the paper more constructive and easy to understand. Abstract and introduction is revised. Efforts are made to describe in detail the methodology and data collection process  showing  that the research is based on an innovative approach to measure the quality of the metal coating on PVDF films that hasn't been used before.

 

The analysis of temperature and mechanical effects on piezoelectric oscillators has led to improvement of durability of piezoelectric oscillators:The study suggests  spraying a protective coating on the PVDF film, using an intermediate plastic sheet between the core and the electrodes to prevent the metallization of the PVDF film from wearing away the edge of the electrodes during the flexing of the core of the piezoelectric oscillator. In future works a simulated model of the thermocycling process will be presented.   

 

Point 2: The sufficient motivation to carry out the experiments is missing. Why aging tests are required, how to improve the output and most importantly, discussions on electrical output are either missing or only casually presented. 

Response 2: The authors agree and a section is added to present the electrical output measured after the thermocycling process , the output voltage genarted by each of the samples is plotted togtehr and results are disccused. There is also numerical data to compare the surface resistance vales of Copper-nickel coatings and aluminium coatings. It is found that copper -nickel is more suitable for longetivity and higher tmeperatur applications.

Point 3: Weird mix up of future tense in 'Structure of the energy harvester and experimental design' section. Plenty of experiments were simply followed bizarre 'shall be' forms , which is unscientific. Experiments should be described either in simple past or present tense.

Response 3: Corrections are made as suggested.

Point 4:  There is no graphical presentation of any scientific data presentations: everything was presented in tables. For resistivity and capacitance studies, the proper curves are missing. There were other electric properties that considered more important to generators, such as current and voltage. They are also missing. Despite, the authors claimed that they claim, "Experimental studies have shown that energy harvesters with a PET core and a 270 PVDF film coated with a copper-nickel coating generate ~3.5 times higher output voltage 271 than those with a steel core and an aluminum-coated PVDF film". Where is the voltage plot?

 

 

 

 

 

Response 4: An entire section 3.1 is added in the results sections to present the output volatge results . The voltage was measured before and after the thermocycling test. The values are compared and deductions are made.

All minor comments are considered and changed accordingly,  including relevant references from the MDPI Actuators journal. English proofreading is done and revisions are made

 

Reviewer 4 Report

Comments and Suggestions for Authors

This study utilizes thermocycling to expedite the aging of an energy harvester under examination. The authors offer insight into piezoelectric theory, the harvester's structure, and the experimental setup, including initial parameter measurements and the thermocycling protocol. Some minor revisions are needed to prepare this article for publication.

 

1-    Consider mentioning the novelty or contribution of the study in the abstract.

2-    You should add the significant findings, and the conclusions reached to your abstract.

3-    The initial sentence of introduction could be simplified for a clearer start.

4-    Clearly state the objectives of your research in the introduction. What specific aspects of PVDF coating materials on piezoelectric layers will you be investigating?

5-    Elaborate on why the choice of coating material is crucial in the context of piezoelectric energy harvesters.

6-    Discuss the typical operational environment for piezoelectric energy harvesters in the introduction section.

7-    Share any initial hypotheses regarding the effect of aging, thermocycling, and mechanical impact on the coating material's performance.

8-    Since you mentioned that four samples were tested, consider including statistical data such as standard deviations or confidence intervals along with the average resistance readings.

9-    Specify the duration of the aging test.

10- Provide a brief scientific explanation of why an equal mixture of epoxy and hardener was determined to be the optimal proportion.

11- Explain why metallization chipping, corrosion, or cracks are significant in the context of energy harvester functionality.

12- Discuss the implications of PVDF film delamination in more detail. How does it affect the overall performance and reliability of the energy harvesters? Are there potential solutions or improvements to mitigate this issue?

13- Explain the role of air voids between the PVDF film and the core during bonding.

14- Provide additional context regarding the significance of longitudinal electrode abrasion.

 

15- Discuss the implications of any variations on the reliability assessment.

Comments on the Quality of English Language

The English in the text is generally clear and well-structured. However, there are a few minor issues with word choice and sentence structure that could be improved for better readability.

Author Response

Response to Reviewer 4 Comments

 

Point 1: Consider mentioning the novelty or contribution of the study in the abstract.

Response 1: Authors are grateful to the reviewer for the feedback and encouraging comment. Changes are made to make the paper rmore constructive and easy to understand. Abstract and introducted is revised.

 

 Efforts are made to describe in detail the methodology and data collection process  showing  that the research is based on an innovative approach to measure the quality of the metal coating on PVDF films that hasn't been used before.

Point 2: You should add the significant findings, and the conclusions reached to your abstract.

Response 2: Revision are made as suggested

 

 The authors agree and a section is added to present the electrical output measured after the thermocycling process , the output voltage generated by each of the samples is plotted together and results are discussed. There is also numerical data to compare the surface resistance vales of Copper-nickel coatings and aluminium coatings. It is found that copper -nickel is more suitable for longetivity and higher temperature applications.

Point 3: The initial sentence of introduction could be simplified for a clearer start.

Response 3: Corrections are made as suggested.

Point 4:  Elaborate on why the choice of coating material is crucial in the context of piezoelectric energy harvesters.

Response 4: Change implemented in introduction section. Two paragraphs are added to highlight the importance of choice of coating material.

Point 5: Discuss the typical operational environment for piezoelectric energy harvesters in the introduction section.

Response 5: Change implemented. Examples of typical application environments are suggested.

 

Point 6: Share any initial hypotheses regarding the effect of aging, thermocycling, and mechanical impact on the coating material's performance.

Response 6: Initial predictions are stated in introduction, lines 54-69

 

Point 7: Since you mentioned that four samples were tested, consider including statistical data such as standard deviations or confidence intervals along with the average resistance readings.

Response 7:  The standard deviation is calculated and readings show that parts 1 to 8 have a higher deviation suggesting that these parts have less connectively compared to the parts 9 to 16. This could be because the wear and tear near parts 1 to 8 where the tipmass is fixed. Added to table 2.

Point 8:  Elaborate on why the choice of coating material is crucial in the context of piezoelectric energy harvesters.

Response 8: A paragraph is added in introduction to elaborate

 

Point 9: Specify the duration of the aging test..

Response 9: The test was conducted for 450 hours, added in abstract and methodology section.  

 

Point 10: Provide a brief scientific explanation of why an equal mixture of epoxy and hardener was determined to be the optimal proportion.

Response 10:. Achieving an equal mixture of epoxy and hardener ensures a  balance in the chemical reaction. In other words, it provides the right number of reactive sites in the epoxy resin and hardener to form a well-defined, interconnected network. Deviating from this balanced ratio can result in incomplete curing or an excess of unreacted components, leading to compromised mechanical properties and durability.

This explanation in added in the section 2.3.1.

Point 11:  Explain why metallization chipping, corrosion, or cracks are significant in the context of energy harvester functionality.

Response 11: Elaborated in the discussion section .

 

Point 12:Discuss the implications of PVDF film delamination in more detail. How does it affect the overall performance and reliability of the energy harvesters? Are there potential solutions or improvements to mitigate this issue?

Response 12:  Delamination can lead to very undesirable conditions such as lower durability and reliability, and most likely to electrical short circuits.

The analysis of temperature and mechanical effects on energy harvesters can allow one to improve the durability of energy harvesters by using the following steps:

• spraying a protective coating on the PVDF film, using an intermediate plastic sheet between the core and the electrodes to prevent the metallization of the PVDF film from wearing away the edge of the electrodes during the flexing of the core of the energy harvesters
• Structural design considerations, such as selecting suitable substrate materials, ensuring even stress distribution, and minimizing points of stress concentration, can help mitigate delamination risks.
• Research and development into advanced adhesive technologies, including conductive adhesives or structural adhesives designed for piezoelectric materials, can help enhance the bonding and reduce delamination risks.

Point 13:Explain the role of air voids between the PVDF film and the core during bonding.

Response 13: Explanation is added in discussion section . Air voids not only increase the delamination risks but also lead to inconsistent electrical performance by introducing variability in the electrical connections between the PVDF film and the core. This can result in fluctuations in the generated electrical output.

Point 14: Provide additional context regarding the significance of longitudinal electrode abrasion.

Response 14: Explanation is added in discussion section. The PVDF electrodes connect various components and are responsible for the flow of electrical current. Longitudinal electrode abrasion can result in increased electrical resistance at the contact points, potentially leading to voltage drops, reduced electrical conductivity, and overheating. This can affect the overall functionality and lifespan of electronic devices.

 

Point 15: Discuss the implications of any variations on the reliability assessment.

Response 15: For systems where reliability is a critical factor, such as in healthcare, or aerospace applications, variations can impact safety and risk management. If reliability assessments vary significantly, it may be challenging to determine the level of risk associated with system failure, potentially leading to overestimation or underestimation of risks. Variations in reliability assessments can also have legal and financial implications. Shortly mentioned in introduction.

 

 English proofreading is done and revisions are made 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Author

In the Abstract you must include numerical results that the readers can consider interesting and then they decide to read your manuscript, this is very important

 

Please, the references that I am asking in the discussion are about the improvements of your results vs other results, but not about the way by measuring.

Author Response

Response to Reviewer 2 Comments

 

Point 1: In the Abstract you must include numerical results that the readers can consider interesting and then they decide to read your manuscript, this is very important.

Response 1: The authors are grateful to the reviewer for the positive and encouraging comment.

The following sentence about the numerical results is added to the abstract “The numerical results of the generated output voltage, surface resistance and capacitance values measured before and after the accelerated aging process are presented in this study”

 

Point 2: Please, the references that I am asking in the discussion are about the improvements of your results vs other results, but not about the way by measuring.

Response 2:  We understand the need for the references to compare the improved results, we have mentioned a couple of methods used in other references for coating adhesion testing. The following paragraph is added in the discussion section.  “Apart from the tests used for quality control functions such as thickness, porosity, adhesion, strength, hardness, ductility, chemical composition, stress and wear resistance, there are other other practical ways of testing the surface coating[19]. Machine efficiency, reduced power requirements and longer running life are some of such practical methods. [6], [20]In this study we have measured the surface resistance, surface capacitance and the voltage generated by the harvester before and after the thermocycling test to evaluate the coating adhesion to the PVDF material.”

Reviewer 3 Report

Comments and Suggestions for Authors

I am satisfied with the improvements suggested by me. The literature section still needs improvement, I recommend this paper (Nano Energy 115, 2023, 108707) on hybrid piezo-tribo nanogenerator to be cited in the revised version.

Manuscript can be considered for publication. 

Author Response

Response to Reviewer 3 Comments

Point 1: The literature section still needs improvement, I recommend this paper (Nano Energy 115, 2023, 108707) on hybrid piezo-tribo nanogenerator to be cited in the revised version.

Response 1:   The authors are grateful to the reviewer for the positive and encouraging comment.

We have cited the article mentioned in this following paragraph "One of the factors contributing to the higher efficiency of piezoelectric power harvesters is the durability of the device, which is affected by the different operating conditions, type of piezoelectric material, coating material of the piezoelectric film, electrode material of the harvester, and so on[7]"

We understand the need for the references to compare the improved results, we have mentioned a couple of methods used in other references for coating adhesion testing. The following paragraph is added in the discussion section.  “Apart from the tests used for quality control functions such as thickness, porosity, adhesion, strength, hardness, ductility, chemical composition, stress and wear resistance, there are other other practical ways of testing the surface coating[19]. Machine efficiency, reduced power requirements and longer running life are some of such practical methods. [6], [20]In this study we have measured the surface resistance, surface capacitance and the voltage generated by the harvester before and after the thermocycling test to evaluate the coating adhesion to the PVDF material.”