Review on non-invasive recharging methods for medical implants

Abstract Over the last ten years, medical implants have evolved to become miniaturized smart devices. However, one of the main obstacle of miniaturization is the volume of the batteries. Shrinking them reduces autonomy, which then increases battery maintenance surgeries and the associated risks. Instead, two non-invasive methods to recharge medical implants are currently explored: energy harvesting and wireless power transfer. In this article, we review some of the most studied techniques in these two fields and compare them in the frame of medical implants demands. Wireless power transfer is currently the most studied option as it is reliable, controllable and can be used as a mean of communication. In particular, this article presents two methods of wireless power transfer, using either electromagnetic or acoustic waves, that stand out and that we compare according to different criteria such as power transfer efficiency for miniaturization and implantation depth, and more importantly safety requirements. In that regard, we conclude that most studies are not taking into account the safety requirements during their designing process while claiming to provide enough energy to recharge medical implants. Instead of limiting the emitter power according to medical standards, most studies only focus on the amount of power collected at the receiver, which means ignoring the potential harm on the human body. Now that most techniques are reaching maturity, a new research methodology, embracing medical standards, should be put at the foreground.