A principle uses piezoelectric materials that react with charge separation when deformed by motion or periodic vibration. Piezoelectric generators typically generate large voltages in the range of ten to one hundred volts, but only very small currents. They can be built as a resonant cantilever structure or applied directly to surfaces that exhibit mechanical deformation.
Another method of converting mechanical energy into electrical energy are electrodynamic or inductive generators, where a combination of a magnet and a coil are the key elements for power generation. When a combination of these components is subjected to vibration and the magnet moves relative to the coil, an electric current is induced in the coil. After rectification, this current can be used to charge a battery or capacitor. The voltages of an electrodynamic generator are typically lower than those of piezoelectric transducers. The current can be influenced by the characteristics of the coil and magnet.
Electrostatic generators can also be used to generate electrical energy from vibrations. They are comparable to an electrical capacitor in which one capacitor plate is suspended so that it can move relative to the other. By charging the capacitor when the plates are far apart and discharging the capacitor when the plates are nearby, electrical energy can be generated. With this generator principle, the output power depends on the capacitance value of the capacitor and its charging voltage.