They produce electric charge as they undergo a temperature change. When their temperature is increased, a voltage develops having the same orientation as the polarization voltage. When their temperature is decreased, a voltage develops having an orientation opposite to the polarization voltage, creating a depolarizing field with the potential to degrade the state of polarization of the part. Piezoelectric actuators are usually specified in terms of their free deflection and blocked force. In practice, a bending motor must move a specified amount and exert a specified force, which determines its operating point on the force versus deflection diagram.
Work is maximized when the deflection performed permits one half the blocked force to be developed.
This occurs when the deflection equals one half the free deflection. The expressions listed in the diagrams represent the linear relations measured at low voltages.