**6. Conclusions**

In this paper, a new cylindrical winding structure for WPT systems was proposed. In the proposed design, the Tx coil was wound on a hemicylindrical structure, and the Rx coil was wound on a cylindrical structure. Therefore, the Rx coil could freely rotate within the Tx coil. Different winding methods were presented and compared. The best winding method reduced the leakage of magnetic fields (LMFs) and maintained constant power-transfer efficiency (PTE), while rotating the Rx coil.Design procedures were discussed in detail. Moreover, EMF analysis was done under different rotation angles between 0◦ and 85◦. The leakage of magnetic fields in the coils' vicinities of the chosen design was reduced by 63.6% compared with other winding methods with the same efficiency. Thus, the given design reduces the cost, weight, shielding (if required), and volume of designed WPT coils. A prototype

was built to validate the chosen design. Measurements confirmed that variations of mutual inductance were very low, where *M* varied between 9.94 μH at α = 0◦ and 10.03 μH at α = 85◦. As a result, the WPT system maintained a constant PTE. Efficiency was decreased by only 2.15% when the Rx coil rotated from 0◦ to 85◦. The proposed WPT system is a good choice for power transfer for applications that require angular movements.

**Author Contributions:** Conceptualization, M.A.H. and W.C.; data curation, M.A.H.; formal analysis, M.A.H.; Investigation, M.A.H.; methodology, M.A.H. and W.C.; resources, X.Y. and W.C.; software, M.A.H.; validation, M.A.H.; writing, original draft, M.A.H.; review and editing, X.Y. and W.C.; supervision, X.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to thank the anonymous reviewers for their constructive comments. **Conflicts of Interest:** The authors declare no conflict of interest.
