Metasurface Patch for Wireless Power Transfer in Implantable Devices

Abstract Wireless power transfer (WPT) systems enable the long‐term operation and miniaturization of implantable devices by eliminating the need for battery replacement and wired power supplies. Although wireless power transfer systems for implantable devices are extensively studied, their practical application is still challenging owing to the constraints and requirements of the human body, such as reflection loss owing to differences in the tissue dielectric properties, mm‐sized devices, and electromagnetic (EM) wave attenuation of the tissue. Here, a phase‐gradient metasurface patch is presented to achieve 5.8 GHz EM power focusing at a focal point of depth 10 mm in the tissue via EM wavefront modulation at the skin–air interface. The proposed metasurface patch is fabricated by arranging subwavelength‐thickness (< λ /10) unit cell structures composed of four metallic layers separated by dielectric substrates that exhibit high‐Q resonance properties and a sufficient phase modulation range with enhanced transmission. By applying the fabricated metasurface patch to a wireless power transfer system for implantable devices, it is experimentally confirmed that the transmission coefficient ( S 21 ) is improved by 6.37 dB compared with that of a wireless power transfer system without the metasurface patch. Furthermore, it is confirmed that the transmission coefficient can be maintained for an incident angle variation up to 30° from the transmitter to the metasurface patch, resulting in a stable power delivery of the proposed wireless power transfer system.