By passing an alternating voltage across
these materials a vibration is produced.
This process is very efficient and almost
all of the electrical energy is converted
into motion. Possible uses of this property
are silent alarms for pagers which fit into a
wristwatch. The vibration is silent at low
frequencies but at high frequencies an
audible sound is also produced. This
leads to the concept of solid state
speakers based on piezoelectric materials
which could also be miniaturised.