Editing Crystal oscillator (section)

==Principle==
A [[crystal]] is a [[solid]] in which the constituent [[atom]]s, [[molecule]]s, or [[ion]]s are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions.

Almost any object made of an [[elasticity (physics)|elastic]] material could be used like a crystal, with appropriate [[transducer]]s, since all objects have natural [[resonance|resonant]] frequencies of [[vibration]]. For example, [[steel]] is very elastic and has a high speed of sound. It was often used in [[mechanical filter]]s before quartz. The resonant frequency depends on size, shape, [[elasticity (physics)|elasticity]], and the [[speed of sound]] in the material. High-frequency crystals are typically cut in the shape of a simple rectangle or circular disk. Low-frequency crystals, such as those used in digital watches, are typically cut in the shape of a [[tuning fork]]. For applications not needing very precise timing, a low-cost [[ceramic resonator]] is often used in place of a quartz crystal.

When a crystal of [[quartz]] is properly cut and mounted, it can be made to distort in an [[electric field]] by applying a [[voltage]] to an [[electrode]] near or on the crystal. This property is known as inverse [[piezoelectricity]]. When the field is removed, the quartz generates an electric field as it returns to its previous shape, and this can generate a voltage. The result is that a quartz crystal behaves like an [[RLC circuit]], composed of an [[inductor]], [[capacitor]] and [[resistor]], with a precise resonant frequency.

Quartz has the further advantage that its elastic constants and its size change in such a way that the frequency dependence on temperature can be very low. The specific characteristics depend on the mode of vibration and the angle at which the quartz is cut (relative to its crystallographic axes).<ref name="Virgil1982">{{cite book|author=Virgil E Bottom|title=Introduction to Quartz Crystal Unit Design|url=https://archive.org/details/introductiontoqu0000bott|url-access=registration|year=1982|isbn=978-0-442-26201-3|publisher=Van Nostrand Reinhold}}</ref> Therefore, the resonant frequency of the plate, which depends on its size, does not change much. This means that a quartz clock, filter or oscillator remains accurate. For critical applications the quartz oscillator is mounted in a temperature-controlled container, called a [[crystal oven]], and can also be mounted on shock absorbers to prevent perturbation by external mechanical vibrations.