**4. Conclusions**

This work presents a 3-coil R-WPT using a pair of driving coils which is intended to provide an improved PTE. The geometries of the coils are optimized through simulations, consequently, the coils achieve their peak *Q*-factors at the resonant frequency. Moreover, the influence of the transfer distance and orientation on the PTE is demonstrated. The results indicate that the proposed design provides a higher PTE than its 3-coil counterpart using only one driving coil in both cases. Finally, the performance of the proposed design is further validated via experiments, and the results show that the 3-coil system using two driving coils provides higher PTE compared to the 2-coil system with an equivalent geometry setting. Besides the PTE, the resonant frequency (or the operating frequency) is another critical factor for implantable applications. The selection of the frequency must be carefully considered in order to avoid safety concerns and electromagnetic wave interference. This will need in-depth and careful studies and further refinement e fforts and will be part of our future work following the current feasibility study.

**Author Contributions:** Conceptualization, C.L. and Y.Y.; methodology, Y.Y.; validation, Y.Y. and R.H.; formal analysis, C.L. and B.W.; writing—original draft preparation, C.L.; writing—review and editing, C.L., B.W., R.H. and Y.Y.

**Funding:** This publication was made possible by NPRP gran<sup>t</sup> NPRP11S-0104-180192 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.

**Conflicts of Interest:** The authors declare no conflicts of interest.
