For Micro Energy Harvesting (MHE), the generation of energy in micro power plants, there are various physical approaches for energy conversion. The conversion of light energy, temperature differences, air currents are only some of them, the conversion of mechanical forces and vibrations others.
In eigenresonance conversion, the vibration of machines is exploited. The energy conversion of such self-resonance sensors can be electromagnetic/inductive, piezoelectric or electrostatic/capacitive. The corresponding sensor is tuned to the resonant frequency of the machine. Such an intrinsic resonance sensor consists of an inertial mass that is elastically suspended. In the inductive conversion, there is an inductance in the inert mass which moves against an electrode. The self-resonance of the mass and electrode corresponds to the vibration frequency of the machine and is excited to vibrate by it. An induction voltage is generated by movement between the electrode and the inertial mass. In piezoelectric resonance method, a piezoelectric bending bar is bent and in electrostatic conversion, electrostatically charged plates move against each other.
The efficiency of the self-resonant sensor is therefore highest at the resonant frequency. If the resonance curve is damped somewhat, then vibrations that lie next to the resonance frequency are also converted.