On the frequency up-conversion mechanism due to a soft stopper by the example of an electrostatic kinetic energy harvester

Micro- and meso-scale electrostatic energy harvesting systems have high efficiency at the higher-frequency part of the spectrum due to the natural frequencies of micro-structures lying over a range from hundreds of hertz to megahertz. However, many real-life applications related, in particular, to wearable systems, structural monitoring, or the Internet of Things, are characterized by low-frequency environmental forces. The main goal of this letter is to demonstrate that the placement of a stopper that limits the motion of the proof mass and causes soft impacts in an electrostatic kinetic energy harvester is responsible for an effect known as frequency up-conversion. This means that there is a significant response to "non-resonant" frequencies away from the natural frequency of the structure leading to effective energy conversion to the electrical domain. The concept summarizing this effect is presented and modeled, and an experiment carried out on a microscopic electrostatic harvester is presented to prove the concept.