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Operation WingChange: ISTF #02-0433








The piezoelectric effect is the tendency of some materials to change their dimensions when an electrical current is applied through them. In the direction that the current flows, they increase in length. In the other two perpendicular dimensions, their length shrinks. The following video, used courtesy of NASA, demonstrates this phenomena.

Divx 4.7 MB download Divx codec/player
QuickTime 2.1 MB download QuickTime Player

The Curie brothers first observation was the charge of crystals when mechanical stress is applied. Rochelle salt's properties were observed by Pockels in 1894 (Germany). In 1921 Valsek saw the loop of the polarized Rochelle salt and its electrical field axis. Later in 1935 Busch and Scherrer from Switzerland discovered what was later known as the second family of piezoelectrics. After 1917 they found a commercial use for piezoelectrics, they could use an ultrasonic submarine detector, sonar. In 1946 they found they could observe the piezoelectric effect on more than one single crystal material which now saved much more money. Presently piezoelectric materials are most commonly used in AC circuits. They are used to create a small vibration, perhaps resulting in the production of sound or a spark for a lighter

However, The movement of individual Piezo actuators when used in a D.C. circuit can be compounded by placing them in series.  They can further be magnified into a bending action much the same way that bimetallic thermometers bend enormously when their materials ever slightly change in length. Static operation, even holding heavy loads, does not consume power.

The way that PZT works is using a combination of chemical effects, physical effects, and geometry. PZT crystallites are centro-symmetric cubic (isotropic) before poling and after poling exhibit tetragonal symmetry (anisotropic structure) (1). 

When an electric field is applied (and the crystal becomes "poled"), a variety of things happen. First, the Zirconate Titanate is pulled toward the positive potential. The lead crystal around it will change in dimensions to accommodate the new position of the Zirconate Titanate. As a result, there is a distortion that causes growth in the Dimensions aligned with the field and a contraction along the axes normal to the electric field. This, magnified to the molar level, is what causes the piezoelectric effect.

In the following original Bryce animation created by Jamie Burch, you will see a PZT crystal initially un-poled. The electrical field will gradually be applied until the crystal is completely polarized. Then, the electrical field will slack off, and the crystal will revert to its original un-poled state.

Microsoft Video 3.5 MB
Divx 0.6 MB download Divx codec/player
QuickTime 3.1 MB download QuickTime Player

Images used with the permission of Jamie Burch
Adapted from Physik Instrumente Tutorials

There are many other types of piezoelectric materials, but they all operate on the same principal.

Most of the concepts for discrete actuator piezo-elements were developed during the peak of research activities in the middle of the 20th century or short thereafter. Multi-layer stack actuators, an actuator design yielding higher performance and still widely used today, was also developed during that period. However, the past five years has shown a boom in the piezo-market economy. Many new innovations on piezoelectrics have created an atmosphere of double digit annual growth. The reason is that piezoelectrics play a large part in wireless communications. For other examples of how piezoelectrics are used, reference Component One.

NASA: LaRC Morphing Project
Sensor Technology Limited
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