How Do Quartz Crystals Vibrate When Electrified in Watches?

[rczmiller]

I am interested in finding out some details concerning vibrations of quartz as it is used in quartz watches. How can I calculate the amount of vibration for a specific size of quartz crystal when an electrical charge is applied?

Example: For a 1 cm cubic crystal of quartz, how fast would the crystral vibrate per second and what is the distance traveled by the molecules at the edge of the crystal? How would this change for a crystal that was 1 meter in length?

I have been looking at several different sites to try to calculate these details, but have not beed able to find any details on how to calculate this. Any help?

 

[Pieter Kuiper]

A piece of quartz is making vibrations just like any other piece of rigid material. A rod will have a resonance for longitudinal vibrations when the wave lenth of sound waves inside the crystal is half the length of the rod. Bending modes will have much lower resonance frequencies.

So it depends on the design (also, there are different "cuts" in quartz), but in general larger will be slower.

The piezoelectric effect in quartz just makes it easy to couple the mechanical vibrations to an electrical circuit. This supplies a little bit of energy (so that the amplitude of vibration does not decay), and it is used to read out the frequency.