When crystals of certain materials, such as quartz, are subjected to mechanical stress, an electrical potential is produced across the crystals.
The process is reversible. A potential electrical difference across the crystal will physically distort the crystal.
The best known simple application of piezo-electric energy is the sparking lighters that ignite gas in grills or barbecues or cooktops, but the piezo-electric principle is also used in pressure sensors, and in some electronic fuel injection systems.
