Purpose/Function of Quartz

Piezoelectric effect
A thin plate made from quartz (c) is coated with a conductive material (a), (b) on two opposite sides (refer to illustration). If a tensile or compressive force now acts on the arrangement, a voltage u develops between points (d) and (e). The polarity of the voltage generated depends on the type of force (tensile or compressive).

Reverse piezoelectric effect
If by contrast a voltage is applied to points (d) and (e), the length of the quartz plate increases or decreases.

Purpose
Mechanical vibrations can be converted into electrical oscillations using the piezoelectric effect: e.g. for microphone, knock sensor and pressure sensor.

Electrical oscillations can be converted into mechanical vibrations or movements using the reverse piezoelectric effect: Piezo loudspeaker, actuator.

Both effects are used in combination in the oscillator crystal: If an alternating voltage is applied to points (d) and (e) where the frequency roughly corresponds to the mechanical resonance frequencies (first harmonics or harmonics) of the quartz plate; the quartz is excited to resonance vibrations which stabilize the frequency of the electrical oscillations. Oscillator crystals are therefore often used where high frequency stability is important. For example in clock-pulse generators (oscillators) for electronic clocks and microprocessors.