How Piezo Electric Crystal works?

Piezo Electric Crystal Operation

(Please see the figure as per the number and read the explanation for each step.)

1. Normally, the charges in a piezoelectric crystal are exactly balanced, even if they're not symmetrically arranged.

2. The effects of the charges exactly cancel out, leaving no net charge on the crystal faces. (More specifically, the electric dipole moments—vector lines separating opposite charges—exactly cancel one another out.)

3. If you squeeze the crystal (massively exaggerated in this picture!), you force the charges out of balance.

4. Now the effects of the charges (their dipole moments) no longer cancel one another out and net positive and negative charges appear on opposite crystal faces. By squeezing the crystal, you've produced a voltage across its opposite faces—and that's piezo electricity!

(Courtesy: www.explainthatstuff.com)