Piezoelectric crystals are one of many small
scale energy sources. Whenever piezoelectric crystals are
mechanically deformed or subject to vibration they generate a
small voltage, commonly know as piezoelectricity. This form of
renewable energy is not ideally suited to an industrial
situation.
The ability of certain crystals to generate Piezoelectricity in
response to applied mechanical stress is reversible in that
piezoelectric crystals, when subjected to an externally applied
voltage, can change shape by a small amount. This deformation,
though only nanometers, has useful applications such as the
production and detection of sound.
Probably the best-known use of piezoelectric crystals is in the
electric cigarette lighter. Here, pressing the button causes a
spring-loaded hammer to hit a piezoelectric crystal, the high
voltage produced by this ignites the gas as the current jumps
over a small spark gap. This technique also applies to some gas
lighters used on gas grills or stoves.
Another common usage of a piezoelectric crystal energy source is
that of creating a small motor; such as that used in a reflex
camera to operate the auto focus system. These motors operate by
vibration. The two surfaces are forced to vibrate at a phase
shift of 90 degrees by a sine wave that has been generated at
the motors resonant frequency. This forces a frictional force
where the two surfaces meet and as one of the surfaces is fixed
the other is forced to move.
It has been found that piezoelectric crystals that have been
embedded in the sole of a shoe can yield a small amount of
energy with each step. This could be applied in a way that the
power for instruments such as torches, cell phones or other
entertainment devices can be sourced from the movement of the
operator.
