Pyroelectric Crystal - Piezoelectric Effect

Piezoelectric Effect

The piezoelectric effect was discovered in the early 1880s by Pierre and Jacques Curie. They found that when pressure is applied to certain crystals (such as quartz or ceramic), an electric voltage across the material appears. The word piezo- comes from the Greek word piezein meaning to press tight, to squeeze. The phenomenon is due to the asymmetric structure of the crystals, that allows ions to move more easily along one axis than the others. As pressure is applied, each side of the crystal takes on an opposite charge, resulting in a voltage drop across the crystal. This effect is linear, and disappears when the pressure is completely taken away.

Piezoelectric materials have wide applications as transducers - transferring mechanical motion into electricity or electricity into mechanical motion. One of the most widespread examples is a quartz resonator. The quartz resonator converts the electrical potential energy of a battery into a steady beat that becomes the oscillator (counter) of a watch. Other common examples include cigarette and gas burner lighters which produce a spark, buzzers found in microwave ovens and phones, tiny microphones and earphones, and inkjet printers (specifically the Epson brand).

Today, examples of the inverse piezoelectric effect can be seen more readily. The inverse effect uses a voltage applied to a piezoelectric crystal to bend it in a desired direction. By constructing a tube with three piezoelectric crystals, motion can be achieved in all three dimensions. Because of their high precision (on the nanometer scale!), these piezoelectric tubes are used in cases where small controlled motion is necessary.

One use of a piezoelectric tube is in an Atomic Force Microscope (AFM). This instrument can create images of objects on the micrometer scale by moving a cantilever tip with respect to a sample surface using a piezoelectric tube. By changing the voltage input to the tube in the AFM, one can control the position of the cantilever tip. More applications of the piezoelectric effect include unimorphs, bimorphs, and stacks.