I went to a very informative seminar this morning by Peter Pott, of the Technical University, Darmstadt, Germany. He gave a very nice introduction to the world of piezoelectric devices.
In short, a piezoelectric thing is something that acquires a voltage across it when it is squeezed, stretched, sheared, etc. They can be used as sensors, e.g. in microphones, or, perhaps more usefully, as actuators. In the case of an actuator, you would apply a voltage to the material, and it would distort accordingly. That means you can use them to move things in response to an electrical stimulus.
Of course, electric motors do the same, but tend to be big and involve lots of parts. A piezoelectric device is dead simple, really.
Possibly the most familiar example is in gas lighters – squash a crystal and it gives enough voltage to throw a spark across a gap, which will ignite the gas. More high tech, but also now well used, is controlling the fuel injection within a diesel engine. This application is pretty taxing for the piezo-device, because it gets so hot, close to the so-called Curie temperature at which the crystals change their structure and lose their piezoelectric state.
Other examples include precise control of mirrors in telescopes (adaptive optics) to ‘cancel’ the distortions imposed by the atmosphere; some very, very cool motor designs, including the famous Burleigh Inchworm, which can position an object extremely precisely; and active control of vibrations.
Finally, Peter explained that since a Piezoelectric device doesn’t have any electric current flowing through it, it isn’t magnetic (unlike a motor) and so you can use them safely in conjunction with MRI machines.
Overall it was a nice seminar and I learnt a lot about these devices, particularly about the very many places where they are used.