The piezoelectric effect manifests itself as a transfer of electrical energy to mechanical energy and vice versa. Observable in many crystalline materials, materials such as quartz, Rochelle salt, and lead titanate zirconate ceramics display the phenomenon strongly enough for it to be of practical use.

The direct piezoelectric effect consists of an electric polarization in a fixed direction while the piezoelectric crystal is deformed. The polarization is proportional to the deformation and causes an electrical potential difference over the crystal. The inverse piezoelectric effect, on the other hand, means that an applied potential difference
induces a deformation of the crystal - a useful property in actuators.

The piezoresistive effect is closely related to the piezoelectric effect. In this case, the material's
conductivity changes when the material is subjected to an external force. Such materials can
also be used in sensor applications.

Piezoresistive Elevator Button

In this example, a force, acts on the elevator button’s upper boundary. The animation shows the resulting boundary displacement in the vertical direction. The slice plot shows the electric conductivity in the piezoresistive domain, illustrating how the conductivity changes with increased deformation.