Wireless Power Transmission Efficiency Improved by Conformal Phase Gradient Metasurface for Implanted Devices

To enhance the efficiency of wireless power transmission for the implanted medical system, a human body surface conformal phase gradient metasurface (PGMS) has been designed in this letter. Based on geometric phase modulation, the PGMS can convert the spherical wave from the transmitting antenna into a plane wave, ensuring the electromagnetic wave perpendicular to human skin. Thereby the power transmission efficiency of the implanted system can be increased obviously. A three-layered cylindrical human tissue model, including skin, fat, and muscle layers, is used to analyze the performance of the PGMS. Simulation results show that the transmission coefficient amplitude of the metasurface element at 1.4 GHz exceeds 0.8. Then the spherical wave of the antenna converted into a plane wave is verified by a 3 × 3 PGMS array when the transmitting antenna is located 50 mm away. Finally, the measurement results have been obtained, which exhibit very good agreement with the simulation. The distinctive advantage of the designed PGMS lies in its flexibility, allowing it to be easily bent and conform to the contoured surfaces of the human body. Additionally, the PGMS offers seamless integration into various medical devices and implants, further enhancing its practicality. This research showcases the potential of the proposed PGMS in significantly enhancing wireless power transmission efficiency for implanted medical systems.