A Flexible Wireless Sacral Nerve Stimulator Based on Parity–Time Symmetry Condition

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Page 4, line 140, can the author describe what is the material surrounding each coil, which models are used in the body and which ones are have air as the media between the coils. The results of inductance calculation and mutual coupling will be strongly influenced by the surrounding media, in particular if it contains tissue.

Page 5 , line 155, in the simulation the coil configurations are changed, what is the block shown in figure 2, does this represent the human tissue ?  What model of dielectric properties is used for this block in the calculation on page 3 and simulation on page 5.

Page 5, line 173, can the author comment on what is the transmission efficiency when the coils are not co-axially aligned, as all of the examples show coils on same axis. Does this have a significant impact on the power transfer and the resonance compare the bending of the coil ?

Page 6, Figure 3, there is no diode rectifier in the receiver circuit ?

Page 7, line 212, the word “tubes” is not clear is this referring to the FET devices ? Can the author please clarify.

Page 7, line 227, the word “tubes” is used but not defined, please explain what is meant here.

Page 8, Figure 5 (b) shows  PCB with components on it, however there is only one component shown in the figure 3 in the receiver circuit, please explain what components are on the PCB to make circuit operate as efficient receiver.

Page 10, line 320, can the author more clearly describe what is indicated by “Pig Skin” for the experiment of tissue penetration of the fields between transmission and pick up coil.

Page 11, line 340, the diagram indicates some potential implant site for pick up coil. However, what are the requirements for encapsulation of materials implanted in this part of the body ? Are there requirements and limitations in choice of mechanical and chemical surface properties to avoid foreign body reaction and are there any requirements for reducing potential leaching of soluble chemical components from within the coil and circuit structure back into the body fluid over an extended period of time ?

Page 11, line 344, is the SNM stimulator already commercialized as a product, what is the physical size and weight ? Is this kind of SNM available for human use, it was not clear if this is also a prototype ? How is the coil connected to the SNM, there don’t seem to be any place for the rectifier or capacitor in the receiver coil circuit design in figure 3. Can the author please explain more clearly.

Comments on the Quality of English Language

minor edits for definitions of some technical terms used in paper.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript describes a wireless power-transferring (WPT) system for a flexible wireless sacral nerve stimulator. In this system, the parity-time symmetry principle was used to ensure efficient and stable wireless power transmission. The design includes modeling, simulation, and in-vitro validation. etc. The authors declare that this system could achieve 78% transmission despite the 15 mm fat-skin tissue and the misalignment and bending during the body movement. However, I am not convinced that their system will work on humans. There are several issues that need to be addressed before the next evaluation:

1.     In the simulation model, it looks like they treat skin tissue as air, which I believe the difference between electrical conductivity and magnetic permeability of skin tissue and air will have a huge effect on the simulated results. They decided to use a flexible receiving coil, however, they simulated 6 conditions, and only one was a flexible receiving coil (coil bending in the center in Z direction only). Overall, I would suggest a more complicated simulation model should be applied.

2.     In Table 1, the geometry of their transmission coil and receiving coil is not clear.

3.     In the results part, the authors declared they used pig skin to represent the human tissue. Based on Figure 8(a), I think it is misleading and lacks detailed information about the pig skin. And I don’t think a single cylinder could mimic human butt movement.

4.     Figure 7 is not clear and difficult to read.

5.     Why did the authors choose 600khz as the frequency which does not lie on the standard of ETSI that will limit the development of their system?

6.     In the discussion part, the authors declared that their system could wirelessly charge the stimulator. I assume there is a battery in the SNM stimulator. I think a battery charge-discharge curve parallel to Figure 9 (c) would be more convincing instead of Figure 9 (c) only.

Comments on the Quality of English Language

The English-writing quality looks fine to me.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The work on a flexible, wireless sacral nerve stimulator based on parity-time symmetry is innovative, particularly in its application of wireless power transfer and the flexibility of the device, which enhances patient comfort. The efficient power transmission and safety are commendable, addressing key challenges in medical implants. However, the study could benefit from further refinement, perhaps in optimizing the device's power management and ensuring its long-term efficacy and stability in a real-world clinical setting.

The article discusses and presents a device for monitoring Lower Urinary Tract Dysfunction that would be inserted into a person's buttocks. I believe this would encounter ethical problems for application. What would be the best way to test the device on humans and what challenges would this face? It would be interesting if the authors discussed this point in the text.

Can you elaborate on how parity-time symmetry enhances the wireless power transfer in the device?

What are the specific challenges in wireless power transfer for medical implants that this research addresses?

How do the safety standards applied in this study compare to those typically required for medical devices?

What future research or development steps are needed to transition this technology from experimental to clinical use?

The authors present 9 figures, some have a complete legend, however, there are others where the legend does not include the entire figure and it is not discussed in the text. I would suggest the authors rewrite these subtitles and improve their discussions within the text.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Revised manuscript is much improved.

Comments on the Quality of English Language

acceptable