A comprehensive review of powering methods used in state-of-the-art miniaturized implantable electronic devices.

Microfabrication techniques that allow the integration of all the components in compact and effective volumes, along with the developments observed in sensor and actuator miniaturization, optimization of microelectronic circuits and, ultimately, wireless communication capabilities, have provided the tools required to develop implants for applications so far technically impossible. However, the scaling down of implantable devices raises the problem of how to power them, since batteries have not scaled down as much as the implants. Consequently, energy sources for implantable electronic devices that do not rely on, or at least mitigate, the requirement for a battery are emerging at an astonishing pace. This paper presents a comprehensive review of recent implantable bioelectronic devices that employ alternative powering methods such as energy harvesting and wireless power transfer. A comparison between the different powering methods is provided, along with a discussion of how these may be suited for the device of the future.