Design of a 3D multilayer out-of-plane overlap electrostatic energy harvesting MEMS for medical implant applications

This paper presents an innovative inertial electrostatic energy harvester for powering active medical devices implanted in the heart by scavenging the heart beat vibrations. The design of the electrostatic device has to overcome several challenges related to the very low frequencies of the mechanical excitation, the need for high reliability and more than ten years durability. Analytical and numerical modelling of the electrostatic device was carried out to maximize the capacitance variation, in order to maximize the energy conversion capability of the device. Optimization of the spring shape has been performed using numerical modelling to minimize the stress concentration in the flexible parts of the MEMS structure. Finally, based on a behavioral model including the electronic interface, we estimated that the device will be able to harvest about 10 μW average power in pulsed mode with 20 V DC output voltage for the electronic interface and 20 Hz resonant frequency, corresponding to 74 μW/cm³ power density.