  The need for wearable or abandoned microsystems, as well as the trend to a
lower power consumption of electronic devices, make miniaturized renewable
energy generators a viable alternative to batteries. Among the different
alternatives, an interesting option is the use of inertial microgenerators for
energy scavenging from vibrations present in the environment. These devices
constitute perpetual energy sources without the need for refilling, thus being
well suited for abandoned sensors, wireless systems or microsystems which must
be embedded within the structure, without outside physical connections.
Different electromagnetic energy scavenging devices have been described in the
literature [1,2,3], based on the use of a velocity damped resonator, which is
well suited for harvesting of vibrational energy induced by the operation of
machines. These vibrations are characterized by a well defined frequency (in
the range between few Hz's and few kHz's) and low displacement amplitudes.
Adjusting the resonant frequency of the system to that of the vibrations allows
amplification of these low amplitude displacements. Moreover, for these
applications, the use of an electromagnetic device has the potential advantages
of a good level of compatibility with Si Microsystem technology, as well as the
possibility of relatively high electromechanical coupling with simple designs.
