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Piezoelectric Effect

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Quartz Crystals

Some materials like quartz show the piezoelectric effect.
When a voltage is applied, the material deforms.
The effect works in reverse too.
If the material is deformed by an external force, a voltage is produced.

Quartz is a very hard crystalline substance that shows the effect strongly. Quartz is also mechanically and chemically stable so it doesn't change or deteriorate with time. A quartz crystal cut to the correct size and shape will ring like a tuning fork producing an AC output on a precise frequency determined by the dimensions of the crystal. This effect can be used to build an oscillator. They are used for extremely accurate frequency generation for radio transmitters.

The effect is also used to focus the LASER that reads data from CD and DVD disks. Anti camera shake technology uses the effect too. Most surprising is the gas stove lighter where the quartz deformation produces a potential difference big enough to make a spark.

Piezoelectric Sounders

Small sounders use this effect to convert alternating voltages into mechanical vibrations and sound.

This effect is used to make sounding devices.

If an alternating voltage is applied to the conducting surfaces, the quartz vibrates and sound is produced.

Versions of this device exist with built-in electronics to produce the alternating voltage.

If the simpler version is chosen, you have to build your own astable circuit to produce the alternating voltage.

These sounders are found in Christmas and birthday cards as well as low cost alarm clocks.