Electrical charge equilibrium and the piezoelectric effect

Question

About the piezoelectric effect: if I press a crystal the electrical charges segregate and an electrical voltage appears on the other two faces of the crystal.

See this link for example:
http://www.explainthatstuff.com/piezoelectricity.html

If I connect the two opposite faces with a wire, an electrical current will flow.
The questions is what happens next, if I keep the crystal pressed (with or without the wire connected - I think it's the same thing)? 
I mean, the mechanical stress is still present, but the electrical charges in the deformed crystal are now in some kind of equilibrium? 
How is that possible, if pressing the crystal deformed the crystal structure so that the electrical charges are “separated” ?
What happens now if I disconnect the wire and release the crystal?
Would that disturb again and produce a new disequilibrium in electrical charges?
What would be the new equilibrium?

George Herold · Answer

So you might want to read this wiki article
I like to think of a piezo as a voltage source (pressure dependent), with a series capacitance, (and then some leakage resistance.)
When you squeeze it you generate some voltage on the cap, but it leaks off.  When you release the pressure then you get opposite sign of voltage for a time.  (That assumes you are squeezing and releasing slowly.)

Electrical charge equilibrium and the piezoelectric effect

One Answer

Add your own answers!

Ask a Question