**5. Conclusions**

Both resonant and non-resonant high-frequency rotary transformers have been designed and compared within an electrical frequency range up to and including 1 MHz. The objective was to realize an output power level of at least 100 W. A multi-physical design approach has been proposed, in which magnetic, electrical, and thermal models are coupled. A design optimization for two fixed pot core geometries (P14/8 and P18/11 pot cores, respectively) in which the efficiency was maximized, has indicated that the application of series–series resonance within the investigated frequency range, increases the output power on average by 39.7% and 45.5%, respectively.

A geometrical optimization, in which the core inertia was minimized for the desired output power, has indicated that with respect to the optimal non-resonant design, the optimal resonant design reduces the core inertia by 45.5%, while the output power and efficiency are increased by 9.3% and 0.4%, respectively. Furthermore, with respect to the fixed core geometry, improvements in terms of core inertia of 38.2% and 66.4% are obtained by the non-resonant and resonant design, respectively.

The multi-physical design approach has been experimentally verified and closely matches the measurements; maximum discrepancies between the model and measurement results of +0.49%, −3.1%, +5.4% and +10.1% were obtained in the output power, efficiency, secondary and primary core temperature, respectively. Therefore, the multi-physical design approach has proven to be accurate and well-suited for the design of high-frequency WPT systems.

**Author Contributions:** The results presented in this paper have been developed by K.B. The analysis has been performed in cooperation with D.C.J.K., S.J., and E.A.L. The paper was written by K.B., and contributions and improvements to the content have been made by D.C.J.K., S.J., and E.A.L. All authors have read and agreed to the published version of the manuscript

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

**Acknowledgments:** The author would like to thank Bram Daniels for his help in realizing multiple design optimization routines to be evaluated in parallel.

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