A Fully Featured Thermal Energy Harvesting Tracker for Wildlife

Round 1

Reviewer 1 Report

1. The manuscript describes the design, implementation and experimental verification of an animal-tracking system powered by thermal energy harvesting.  
2. The topic of the manuscript is significant and relevant to the journal. The work is technically sound and original. The manuscript is described very well in detail. The work is an extension of their earlier work (references 7-9), but more than enough new material is presented in this manuscript. Its main strength is the detailed description, implementation and pratical testing of an animal-tracking system soley powered by thermal energy harvesting. This is highly original. A (small) weakness is the limited testing period in the field, in particular since several devices broke during the testing.  
3. We have the following recommendations for the improvement of the manuscript:   More related work regarding the energy harvesting of on body animal sensors would significantly improve the introduction. Related work with regard to solar energy harvesting and thermal energy harvesting was described, but other energy harvesting techniques are lacking, e.g., radio frequency, inductive coupling, and piezoelectric. Some possible references are, for example,  

• Luo, Y., Pu, L. and Zhao, Y., 2018. RF energy harvesting sensor networks for healthcare of animals: Opportunities and challenges. arXiv preprint arXiv:1803.00106.  
• - Minnaert, B., Thoen, B., Plets, D., Joseph, W. and Stevens, N., 2018. Wireless energy transfer by means of inductive coupling for dairy cow health monitoring. Computers and Electronics in Agriculture, 152, pp.101-108.  
• - Dagdeviren, C., Li, Z. and Wang, Z.L., 2017. Energy harvesting from the animal/human body for self-powered electronics. Annual review of biomedical engineering, 19, pp.85-108.  

It would be interesting to discuss -if possible- as to why not all collars did work during the whole period. Was it purely a mechanical issue of the collar, or do the authors think other reasons could apply?  

Finally, we would encourage the authors to continue on their path, and to perform more field experiments (more collars during a longer period, also in winter) to obtain more data, but we understand that this is beyond the scope of the current manuscript.

Author Response

Dear Reviewer,
We would like to thank you for the thoughtful comments and feedback four our manuscript. 
As recommended, we slightly extended our introduction with more related work regarding possible energy harvesting techniques at the animal. We thank for the input of related research.
We also clarified  in our paper the reason for the collars' outages. These were caused solely by the same mechanical issues: The attachment of the harvesting housing to the main collar was not strong enough and broke, leaving the housings connected together solely by the electric wires. We are going to improve this when used in future experiments over an extended period.

Reviewer 2 Report

1. With the larger temperature difference, there is much more power available in the device during the night. However, it is thought that the position and activity monitoring is more needed during the daytime for the goat (although it depends on the activity pattern of the animal species).  Therefore, it is strongly recommended that the device needs additional longer period of power storage like battery so that the power harvested during the night can be used in the daytime when various functionalities are required.  
2. There are a couple of functionalities related to animal health which can run with much smaller electric power than equired for GPS. It would be more beneficial to the related research fields. 
3. Authors can provide results about the measured activity (position) data from field test which is the ultimate purpose of the proposed device. 

Author Response

Dear Reviewer,
We would like to thank you for the thoughtful comments and efforts towards improving our manuscript. 
Concerning your request about results of the measured activity, we slightly extended the results section with data from the accelerometer.
We agree that GPS may not be a good choice with regard to monitor the animals' health due to its high power consumption. In fact, we integrated GPS with regard to its use in studies analysing migratory paths of wild animals. In our experimental setup, GPS is used to gain data and experience for its future usage on animals like the lynx.
Your advice about a larger energy storage is totally right, we are already thinking about enlarging the capacity at least to the extend that one day may be covered without compromising too much on higher leakage of the capacitor or battery.