**5. Conclusions**

In this paper, a novel 1-bit coding metasurface is proposed and implemented for WPT systems. The coding metasurface is capable of adaptively focusing and steering beam to enhance power transfer efficiency in WPT systems. The proposed metasurface comprises 16 × 16 compact unit cells which were designed with a fractal structure and an operating frequency of 5.8 GHz. Indeed, both simulations and experiments were conducted to validate the theory. It was demonstrated that the proposed coding metasurface is able to focus the beam to the desired direction with a wide range from −60◦ to 60◦ in the elevation angle. For the adaptive beam to be focused on the mobile receiver, the adaptive optimal phase control scheme was proposed and applied. The results prove that the optimal one surpasses the random phase control and beam synthesis schemes. At 50 cm, the coding metasurface with the optimal phase control scheme can provide approximate 4% of power transfer efficiency, while it is just about 3% in the beam synthesis scheme.

**Author Contributions:** Conceptualization, N.M.T.; Methodology, N.M.T.; Software, N.M.T. and M.M.A.; Validation, N.M.T., M.M.A., J.H.P. and S.I.H.; Formal analysis, N.M.T., M.M.A.; Investigation, N.M.T., M.M.A. and J.H.P.; Resources, J.H.P., S.I.H.; Data curation, N.M.T.; Writing—original draft preparation, N.M.T.; Writing—review & editing, K.W.C. and D.I.K.; Visualization, N.M.T.; Supervision, K.W.C. and D.I.K.; Project administration, K.W.C. and D.I.K. All authors have contributed to the editting and proofreading of this paper.

**Funding:** This research was supported in part by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (2014R1A5A1011478), and in part by the MSIT(Ministry of Science and ICT), Korea, under the ITRC(Information Technology Research Center) support program(IITP-2019-2016-0-00311) supervised by the IITP(Institute for Information & communications Technology Planning & Evaluation).

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