This paper reviews the state-of-the art in vibration energy harvesting for
wireless, self-powered microsystems. Vibration-powered generators are
typically, although not exclusively, inertial spring and mass systems. The
characteristic equations for inertial-based generators are presented, along
with the specific damping equations that relate to the three main
transduction mechanisms employed to extract energy from the system.
These transduction mechanisms are: piezoelectric, electromagnetic and
electrostatic. Piezoelectric generators employ active materials that generate
a charge when mechanically stressed. A comprehensive review of existing
piezoelectric generators is presented, including impact coupled, resonant
and human-based devices. Electromagnetic generators employ
electromagnetic induction arising from the relative motion between a
magnetic flux gradient and a conductor. Electromagnetic generators
presented in the literature are reviewed including large scale discrete devices
and wafer-scale integrated versions. Electrostatic generators utilize the
relative movement between electrically isolated charged capacitor plates to
generate energy. The work done against the electrostatic force between the
plates provides the harvested energy. Electrostatic-based generators are
reviewed under the classifications of in-plane overlap varying, in-plane gap
closing and out-of-plane gap closing; the Coulomb force parametric
generator and electret-based generators are also covered. The coupling
factor of each transduction mechanism is discussed and all the devices
presented in the literature are summarized in tables classified by transduction
type; conclusions are drawn as to the suitability of the various techniques