Note 1 to entry: Piezoelectric actuators are classified into the single-plate, bimorph, and stacked types, and the popular material is lead zirconate titanate (PZT). The features are: 1) quick response, 2) large output force per volume, 3) ease of miniaturization because of the simple structure, 4) narrow displacement range for easier microdisplacement control, and 5) high efficiency of energy conversion. Piezoelectric actuators are used for the actuators for micromachines, such as ultrasonic motors, and vibrators. An applied example is a piezoelectric actuator for a travelling mechanism, which moves by the resonance vibration of a piezoelectric bimorph, and a micropositioner piezoelectric actuator, which amplifies the displacements of a stacked piezoelectric device by a lever.