**4. Conclusions**

We presented the new concept of a wearable heater that combines IPT techniques and a textile coil. The SN mode for the IPT was adapted in the proposed wearable textile heater to eliminate electronic components in the Rx, improving robustness and user convenience. Since the Tx coil only resonates with the textile Rx coil when both coils are properly placed, the system could save energy and ensure safety if the Rx coil is unintentionally misaligned during operation. We optimized the Tx and Rx coils to minimize PTE loss, and maximize the PDL in SN mode through analysis in the IPT system based on SN topology analysis for wireless-wearable-heater applications. The proposed system provides a very robust wearable heater using IPT technology without any electrical components at the Rx, which dramatically increases convenience for the user. Compared to the conventional SS topology in the IPT, the proposed optimized design showed 160% improved PDL, while PDL was only reduced by 11%, which was well-matched with the theoretical results. Furthermore, the proposed design could inherently prevent energy dissipation from the Tx against misalignment between Tx and Rx due to automatic resonant-frequency shifting in the IPT, resulting in improved safety and e fficiency with no need for complicated sensing and data-communication circuitries in the Rx. Although the proposed wireless wearable heater showed less sensitivity against temperature variations compared to a wired wearable heater due to the lack of sensing circuitries in the Rx, it can be further improved by a transient observation circuit in the Tx to monitor input voltage and current for estimating the delivered power to the heating material, as shown in Figure 7. To the best of our knowledge, this is the first demonstration of a wireless wearable heater using conductive thread, providing textile-coil optimization for SN topology in an IPT system.

**Author Contributions:** conceptualization, B.L. and K.-H.L.; methodology, B.L.; validation, H.K. and B.L.; formal analysis, H.K.; investigation, B.L.; data curation, H.K.; writing—original-draft preparation, H.K.; writing—review and editing, B.L.; visualization, H.K.; supervision, project administration, and funding acquisition, B.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Incheon National University (#2018-0165) Research Grant in 2018.

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