Figure 1. Multilayer piezoactuator, with thin films of PZT separated by conducting layers. Arrows define the direction of polarisation of each layer.
How Piezoelectric Actuators Work
Piezoelectric materials change dimension when an electric field is applied. This change is quite small, ~0.1%, but large forces are generated, ~ 100-1000 N. Since the dimensional change is proportional to the applied field, piezoelectric materials or piezoactuators, are ideal for positioning applications where nanometer sensitivity is required. A typical piezoelectric material is lead zirconium titanate (PZT).
Similarities between Piezoelectric and Magnetic Materials
In many ways, piezoelectric materials are similar to magnetic materials. Both exhibit hysteresis, a Curie Temperature and a poling direction. As the operating temperature approaches the Curie temperature the actuators depole, the domains become unaligned, and the expansion with applied field is greatly reduced.
Piezoactuators in Nanopositioners
Mad City Labs nanopositioning systems use multilayer piezoactuators. A multilayer piezoactuator is a stack of PZT thin films electrically connected in parallel. The thinner the film, the lower the voltage required for maximum expansion of the multilayer stack. The piezoactuators which Mad City Labs uses obtain full scale motion with a driving voltage of 150V. Integrated position sensors and a closed loop control system make it possible to determine the precise location of the nanopositioner and provide the exact driving voltage necessary to eliminate inaccuracies which are inherent in piezoactuators.