Wireless Power Transfer for Implantable Medical Devices: Impact of Implantable Antennas on Energy Harvesting

This paper presents a thorough review of the main techniques used for wireless power transfer (WPT) in implantable medical devices (IMDs) with a specific focus on the techniques that employ implantable antennas for energy harvesting (electromagnetic (EM) WPT techniques). The techniques are first analysed and compared based on the IMD application, power transfer efficiency (PTE), transfer distance, implantation depth, implant size, operating frequency, and specific absorption rate (SAR). The study provides a critical analysis of the main WPT system’s as well as implantable antennas’ design parameters that control the PTE and hence the charging rate of the IMD. The investigated design parameters include the WPT TX-RX antennas’ gain, WPT-RX size, transfer distance, and the WPT TX-RX antennas’ alignment. Tutorial simulation examples are included to showcase the impact of these design parameters on the amount of power coupled to the IMD. The paper also discusses recent techniques used for improving the amount of power received by implantable antennas, and hence higher PTE and IMDs charging rate, namely, the use of implantable MIMO WPT-RX antennas to mitigate antennas misalignment and the use of metamaterial surfaces to focus the power emitted from WPT-TX antennas towards the implantable WPT-RX antennas. The findings and observations reported in this study serve as a valuable resource for designers and researchers to comprehend the effect of various WPT TX-RX antennas design parameters on PTE. The analysis and full-wave simulation examples, included in the paper, are shown very useful in understanding the challenges associated with WPT in IMDs and in proposing potential solutions.