Positive piezoelectric effect: When certain dielectrics are deformed by external forces in a certain direction, polarization will occur inside them, and positive and negative charges will appear on their two opposing surfaces. When the external force is removed, it will return to the uncharged state. This phenomenon is called the positive piezoelectric effect.

Inverse piezoelectric effect: When an electric field is applied in the polarization direction of the dielectric, these dielectrics will also deform. After the electric field is removed, the deformation of the dielectric disappears. This phenomenon is called the inverse piezoelectric effect, or electrostriction phenomenon.