Wireless Power Transfer Using Harvested Radio Frequency Energy with Magnetic Resonance Coupling to Charge Mobile Device Batteries
Round 1
Reviewer 1 Report
Descriptions of the presented block algorithms should be clearer. The units specified in the drawings / graphs must be clearly described. Overall, the article is good.
Author Response
Response to Reviewer 1 Comments
Thank you for your valuable comments and suggestions to improve the quality of our manuscript. Kindly refer to the responses below:
Point 1: Descriptions of the presented block algorithms should be clearer. The units specified in the drawings / graphs must be clearly described. Overall, the article is good.
Response 1: The block diagram (Figure 1) is clearly labelled and detailed description for the block diagram is provided. Graph depicting the input voltage trace analysis inclusive of the units (Figure 4) is clearly labelled. Graph depicting the predicted output voltage (Figure 5) is clearly labelled.
Reviewer 2 Report
Please try to describe the overall efficiency of WPT system. Also will be on interest to sketch a thermal model thatch you help too. Thus you can correlate the input parameters for desi with the operation and you will arrive at pertinent conclusions
The results are on interest, but please present this results detailed in the light of system design parameters and put in evidence the operation phase.
please give more experimental details related experiment an about energy efficiency
line 141 (eq 4.) must be review
Author Response
Response to Reviewer 2 Comments
Thank you for your valuable comments and suggestions to improve the quality of our manuscript. Kindly refer to the responses below:
Point 1: Please try to describe the overall efficiency of WPT system. Also will be on interest to sketch a thermal model thatch you help too. Thus you can correlate the input parameters for desi with the operation and you will arrive at pertinent conclusions
Response 1: Detailed description with calculations was included. Values for the calculations were taken from the simulation test. The research was based on combining RF energy harvesting and magnetic resonance coupling to transfer power wirelessly. Numerous studies were conducted on WPT, with a focus on battery technology. Limited research was done on using an alternate energy source such as RF energy harvesting with MRC.
Point 2: The results are on interest, but please present this results detailed in the light of system design parameters and put in evidence the operation phase.
Response 2: Some additional explanations were included aligned to the results as well as additional formulae. Table 1 was included to clarity the choice of wire for the coils.
Point 3: Please give more experimental details related experiment an about energy efficiency
Response 3: Energy efficiency is aligned on the choice of components. Detailed descriptions were included regarding the prototype circuit (Materials and Methods), additional equations with some calculations were provided in the Simulated Results section. Values provided in the prototype description (Simulated Results) were used for certain calculations. Section 4 highlights the test results for the physical WPT prototype circuit.
Point 4: line 141 (eq 4.) must be review
Response 4: The error in the subscript of equation 4 has been corrected.
Reviewer 3 Report
This presents some ideas and results on a means of wireless charging of batteries. As such it may be good for a student experiment on the topic and a journal on educational topics. But it lacks important material.
- Fig. 1 makes sense since it shows the coils with rectifier and voltage regulator (but not the storage capacitor). However the circuit treated, Fig. 3 is not this but lacks the rectifier and voltage regulator.
- There are errors. For example Eq. (1) has M=L and following that M=kL so k=1. But k is an important parameter and is never determined in the paper (its dependence on coil separation is very important but lacking).
- Symbols are not clearly used. For example, below (1), there is phi_T which is sometimes phi T.
- More important is that the output DC voltage is given as (15), Va=2Vp/Pi. So with Vp given as 6 this gives under 4Volts. But above Fig. 6 it indicates that 9.46V was obtained. Why the difference as this is very important to the success of the method?
- Below Fig. 1 it states that a 2N222A was used. It is not clear where, as this is not a rectifier nor voltage regulator but a bipolar transistor.
- C is used for conductance. However, G is standard for conductance since C is reserved for capacitance and capacitance is crucial to this study. In fact it is large for a mobile device, being 100micro-Farads.
- Critical to the operation is the flux transfer from the primary to the secondary, represented via the mutual inductance. Properly this flux would be determined via Maxwell's equations but in this case is reflected by the coefficient of coupling k, neither of which [flux or k] are calculated or numerically given.
- Since such have been used for charging of pacemakers there are lots of studies on such some more of which should be referenced. In particular of importance is that of interference by stray fields.
- Their previous paper, reference 14, is available through the IEEE and so should be indicated.
Author Response
Response to Reviewer 3 Comments
Thank you for your valuable comments and suggestions to improve the quality of our manuscript. Kindly refer to the responses below:
Point 1: Fig.1 makes sense since it shows the coils with rectifier and voltage regulator (but not the storage capacitor). However the circuit treated, Fig. 3 is not this but lacks the rectifier and voltage regulator.
Response 1: Figure 1, block diagram for the wireless power transfer prototype circuit, has been amended to include the storage capacitor. Figure 3, includes the description of the load as indicated by RL
Point 2: There are errors. For example Eq. (1) has M=L and following that M=kL so k=1. But k is an important parameter and is never determined in the paper (its dependence on coil separation is very important but lacking).
Response 2: The error in equation (1) has been corrected and thus reflects the following:
https://www.elprocus.com/what-is-mutual-inductance-and-its-theory/
Point 3: Symbols are not clearly used. For example, below (1), there is phi_T which is sometimes phi T.
Response 3: It had been corrected accordingly, symbol is clearly represented.
https://shareok.org/bitstream/handle/11244/325036/PiersonC2017.pdf?sequence=1 (page 37)
Point 4: More important is that the output DC voltage is given as (15), Va=2Vp/Pi. So with Vp given as 6 this gives under 4Volts. But above Fig. 6 it indicates that 9.46V was obtained. Why the difference as this is very important to the success of the method?
Response 4: Equation (15) and the other equations was considered for the simulation test (explained in the Simulation Results section), 6 volts was the input voltage to measure voltage loss, resistance, conductance, etc. to check feasibility of the simulated circuit before the prototype model could be built. Section 4 explains the results of the physical prototype model (RF energy harvesting circuit with the magnetic resonance coupling circuit), this being 9.46V.
Point 5: Below Fig. 1 it states that a 2N222A was used. It is not clear where, as this is not a rectifier nor voltage regulator but a bipolar transistor.
Response 5: The description of the 2N2222A transistor attached to the transmitting coil was included Figure 1.
Point 6: C is used for conductance. However, G is standard for conductance since C is reserved for capacitance and capacitance is crucial to this study. In fact it is large for a mobile device, being 100micro-Farads.
Response 6: Equation 14 was amended to include the correct unit for conductance (G) and description for Figure 3 was amended to display C for capacitance (Cp = capacitance at primary coil and Cs = capacitance at secondary coil).
Point 7: Critical to the operation is the flux transfer from the primary to the secondary, represented via the mutual inductance. Properly this flux would be determined via Maxwell's equations but in this case is reflected by the coefficient of coupling k, neither of which [flux or k] are calculated or numerically given.
Response 7: Referring to the description provided for the WPT prototype circuit and Section 3, the following values were included in the calculation of mutual inductance (equation 1), coupling coefficient (equation 3), and average voltage (equation 17). Additional equations were included to flow the calculations stated here. Table 1 displaying the parameter and values for the simulated results is presented.
Point 8: Since such have been used for charging of pacemakers there are lots of studies on such some more of which should be referenced. In particular of importance is that of interference by stray fields.
Response 8: The use of MRC was included as reference (5), charging of pace makers wirelessly. Additional references for WPT in the medical field and interference by stray fields was included in Section 1 (Introduction) as well as ways to minimise magnetic stray fields. Additional references was included regarding challenges with WPT. Thank you for this suggestion.
Point 9: Their previous paper, reference 14, is available through the IEEE and so should be indicated.
Response 9: The citation for Reference 14 is correct and was downloaded as is from the IEE Explore platform. https://ieeexplore.ieee.org/document/7920652
Round 2
Reviewer 2 Report
Please review line 156
Please use the appropriate Greek character for resistivity (see ec. 14, 15, and 16).
Please clarify the Hexadecimal Format in last column of Table 1 (maybe is exponential form of data?!)
Author Response
Response to Reviewer 2 Comments
Thank you for your valuable comments and suggestions to improve the quality of our manuscript. Kindly refer to the responses below:
Point 1: Please review line 156
Response 1: Line 156 was revised to include the description of the coupling coefficient k (now lines 221-223).
Point 2: Please use the appropriate Greek character for resistivity (see egns. 14, 15, and 16).
Response 2: Equations 14, 15 and 16 have been corrected by including the correct Greek character for resistivity known as rho.
Point 3: Please clarify the Hexadecimal Format in last column of Table 1 (maybe is exponential form of data?!)
Response 3: The scientific notation replaces the hexadecimal format for the inductance values for the AWG wire. This seemed to be a neat representation of the inductance values (H) provided in column 5.
Reviewer 3 Report
There is no adequate explanation of how their equation for output voltage does not agree with the experimental results. Also no explanation of why the amplifier transistor is used as a voltage regulator nor circuit showing this.
Author Response
Response to Reviewer 3 Comments
Thank you for your valuable comments and suggestions to improve the quality of our manuscript. Kindly refer to the responses below:
Point 1: There is no adequate explanation of how their equation for output voltage does not agree with the experimental results.
Response 1: LTspice was used for the simulations, the input voltage to the simulated circuit was 6V based on equation 17, and the value of the average voltage is included in Table 1. The output voltage for the experimental results was included in Section 4. The results of the simulation with the estimated 6V were compared to the harvested power/voltage from the RF energy harvesting circuit to be used to charge the mobile device battery wirelessly. To acquire the harvested 9.46V, the capacitor was connected to the RF energy harvesting circuit for a long duration (7.5 hours).
Point 2: Also no explanation of why the amplifier transistor is used as a voltage regulator nor circuit showing this.
Response 2: The voltage regulator is highlighted in figure 1 (H). The purpose and use of the voltage regulator are explained in Section 4. To initiate charge in a mobile device battery (smartphone), 5V is required. The harvested power is stored in the capacitor (G) as explained in Section 2. A voltage regulator is used for two reasons, to regulate or vary the output voltage of the circuit and to keep the output voltage constant at the desired value, despite variations in the supply voltage or in the load current.
Round 3
Reviewer 3 Report
Almost all of the circuits for Fig. 1 are missing and in particular none is shown including the mentioned transistor and how it accomplishes rectification as stated. Since that transistor is not designed for that purpose I can not recommend this for publication until that circuit and its operation are shown.
Author Response
Response to Reviewer 3 Comments
Thank you for your valuable comments and suggestions, kindly refer to the responses below:
Point 1: Almost all of the circuits for Fig. 1 are missing and in particular none is shown including the mentioned transistor and how it accomplishes rectification as stated. Since that transistor is not designed for that purpose I cannot recommend this for publication until that circuit and its operation are shown.
Response 1: Detail descriptions related to block diagram (Figure 1) have been included. Additional references also included within the descriptions provided that were sought during the simulation and the building of the prototype WPT circuit. The block diagram represents two stages of the overall circuit, which are the RF energy harvesting circuit based on our previous research conducted, this has been referenced accordingly and the WPT circuit. The circuit diagram of the magnetically coupled coils that form part of the WPT circuit has been included in this revised version of the manuscript (figure 2).
Author Response File: 
Author Response.docx
