Structural devices
Structural devices

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Structural devices

4 Piezoelectricity: motion from crystals

4.1 The piezoelectric effect

The phenomenon of piezoelectricity was first predicted and demonstrated in the late nineteenth century using naturally occurring materials. It has a vast number of applications, ranging from spark ignitors to inkjet printers. It is also utilised in timing circuits, where an oscillating electric field is used to make a quartz crystal resonate at its natural frequency. In MEMS, the effect is used to generate small-scale movements in a range of devices known as micro-actuators.

The effect is the direct interconversion of mechanical and electrical energy in a material. Only a few materials do this to an appreciable extent. Their response can be summarised briefly by saying that they change their physical shape when electrically stressed (by having a voltage applied across them); and they change their distribution of electrical charge (commonly known as their state of polarisation – I'll come to this later) when mechanically stressed (by being squeezed, bent, or pulled). The material's electrical response to mechanical stress is known as the ‘generator’ effect, and it is this that is described by the word ‘piezoelectric’ – the prefix ‘piezo-’ is from the Greek piezein, to press.

The generator effect is exploited in the spark ignitor. Here, a crystal is sufficiently stressed to generate a voltage across it large enough to make the air (between electrodes attached to it) break down. This creates a spark and is used for lighting stoves the world over. Conversely, a piezoelectric material will change its shape when its ambient electric field changes and this is known as the ‘motor’ effect. It is this effect that is deployed in some inkjet printers. A piezoelectric crystal is used as a piston to launch micro-droplets of ink across the short gap between the print head and the paper. Ink drops can be expelled very quickly (at a rate of tens of kHz) and at high velocity (several m s−1) enabling fast, accurate printing on the page. Figure 18 shows the effects.

This ‘motor’ effect then gives us the possibility of making something move, merely by the application of an electric field. That is to say, we can transduce an electrical signal into physical movement.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has over 40 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus