A wireless power transmission system with load regulation for implantable devices

The application of Wireless Power Transmission (WPT) has attracted more and more attention, but the energy efficiency cannot be high due to the inevitable loss. Energy efficient WPT is increasingly demanded especially in implantable devices due to their wireless inefficiency nature. In addition, many implantable devices include digital circuits such as a Microcontroller Unit (MCU) in which the supply voltage may fluctuate severely with the driving clock of digital circuits switches between ground (Gnd) and supply voltage (Vdd), since the power transmitted wirelessly is limited, and the system may even cut off under wireless charging conditions. Therefore, the load regulation is also required in a WPT system. This paper presents a WPT system with load regulation and optimized antenna design for implantable devices, for which measurement results show that the maximum transmission efficiency can reach 79.3% and it can still necessitate a large dynamic load current range. When the load current is switched between 12 uA and 5 mA, the overshoot and undershoot of the output voltage are 150 mV and 80 mV, respectively. Finally, several state-of-the-art WPT applications in biomedical devices are introduced.