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Introduction to piezoelectricity

PYTHEAS

November 9th 2023

PYTHEAS Technology often introduces itself as a team of experts in piezoelectricity. It is indeed the best way for us to bring together all our activities, but what do we mean by that? We will try to lift the veil on this term which may seem complex at first glance.

What is piezoelectricity ?

Piezoelectricity is the property of certain materials to become electrically polarized under the action of a mechanical force, or to change in shape under the action of an electrical force. To make it simple, imagine a material that becomes electrically charged when you compress it, and which stretches or compresses when you apply an electric field to it.

We speak of the direct piezoelectric effect to refer to the ability of the material to generate an electric charge under the effect of a mechanical force, and of inverse piezoelectric effect to refer to the deformation of the material when an electric field is applied to it.

Which materials are piezoelectric?

Some materials have a crystalline structure that produces an electrical charge imbalance on their surface when mechanical stress is applied, so they are naturally piezoelectric. This is particularly the case for certain natural materials such as quartz, topaz or even tourmaline.

Other piezoelectric materials have been developed by researchers, in particular ceramics, to facilitate their industrial manufacturing and to control and improve their performance. The most widely used of these piezoelectric ceramics is PZT, for lead zirconate titanate. Compared to naturally piezoelectric materials, synthetic piezoelectric ceramics generally have much better properties, with piezoelectric coefficients approximately 100 times higher. This often makes them more profitable and interesting for industrial or everyday applications.

History of piezoelectricity: how was it discovered ?

Piezoelectricity was discovered in 1880 by the French brothers Jacques and Pierre Curie when they observed that certain crystals emit small amounts of electricity when compressed or stretched.

The following year, in 1881, Gabriel Lippmann, a Franco-Luxembourgish physicist, predicted the opposite effect, which would then be verified experimentally by the Curie brothers.

The name “piezoelectricity”, which comes from the Greek “piezein” and means to squeeze, is given to this phenomenon.

The Curie brothers then invented the piezoelectric quartz in 1885, an instrument for measuring weak electrical charges. (Opposite picture: A piezoelectric quartz device that belonged to the Curie Laboratory, Photo: Curie Museum / Uriel Chantraine.)

This instrument would enable a major discovery in scientific history a few years later during Pierre and Marie Curie’s research on radioactivity. This is how in 1898, Marie Curie discovered polonium and radium (which is around a million times more radioactive than uranium).

How is piezoelectricity used nowadays ?

Piezoelectricity may seem so abstract that it is hard to believe we come across it in our daily lives. It is, for example, present in our phones where sensors detect the pressure exerted on the screen, in the speakers, and even in lighters and gas lighters!

Piezoelectricity is also used for more specific applications. We can notably list:

Medical devices such as medical imaging and sensors. Let’s take the example of obstetric ultrasound. This painless examination, which makes it possible to monitor the development of the fetus during pregnancy, is carried out using ultrasound. The probe used, in which there are one or several piezoelectric ceramics, transforms the electrical signals sent by a computer into an ultrasound wave, which propagates through the patient’s body. The ultrasounds pass through the tissues and are reflected when they encounter an obstacle and return to the probe. The probe will then capture these acoustic waves, transform them into electrical signals, and send them to the computer, which can transform these echoes into images. Unlike X-rays, ultrasound poses no danger to humans, making it particularly relevant for medical applications.
Energy harvesting, which we have already talked about in a previous article. Piezoelectric systems can be developed to harvest energy present in the environment, vibrations for example, and transform it into usable energy. Concretely, this may be of interest to different sectors such as connected objects, structural health monitoring, or even portable medical sensors.
Pressure sensors for aeronautics or automobiles, for example. These piezoelectric sensors can measure the pressure of liquid or gas in nozzles or the pressure of car tires.
Piezoelectric motors and actuators. For example, we can find it in the autofocus of cameras, some medical robots or even car electric window mechanisms. Piezoelectric motors have several advantages such as high precision, blocking at rest, or the fact that they do not produce a magnetic field (which makes them particularly suited to MRI scans).
Inkjet printers. Piezoelectric inkjet heads work using a piezoelectric crystal which, when it receives an electrical signal, changes in shape and ejects ink. This type of printer is particularly used for large-format printing.
Transducers for underwater acoustics. Piezoelectricity is used by many devices dedicated to underwater acoustics. It is found in particular in hydrophones, transducers and antennas used for navigation, oceanographic research and sonar systems.

This list of applications is of course not exhaustive; other uses of piezoelectricity exist or are under development. This notorious technology still has a bright future ahead of it!

What does PYTHEAS Technology do ?

As we said in the introduction, PYTHEAS Technology presents itself as a company with expertise in piezoelectricity. All the solutions developed by PYTHEAS Technology indeed use piezoelectricity. Also, the entire team has developed, within the company as well as during previous experiences, solid knowledge and skills in piezoelectricity in different specialties, from modeling to electronics, including mechanical design.

Discover all our technologies and applications on our website and do not hesitate to contact us to discuss your needs and projects.