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Piezoelectric highway

What is piezoelectricity?

Revolutionizing the clean energy sector

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From floors capable of powering the lighting of a business, to revolving doors at a café that provide electricity, there are already various examples of piezoelectric materials that, sooner than later, could revolutionize the clean energy sector. 

Combating climate change has become one of the major battles of the 21st century, and the search for new ways of obtaining clean energy that minimizes our impact on the environment is one of our greatest secret weapons for achieving it. Large corporations are committed to innovation, and the energy and construction sectors are no strangers to a long-distance race in which nature itself provides the most valuable resources on a silver platter. 

Nowadays, it's not unusual to see large areas of land dotted with solar panels capable of transforming the sun's rays into electricity, or to come across fields of wind turbines generating wind energy. However, these areas of innovation continue to expand. 

 

What is piezoelectricity?

Piezoelectricity is the property that certain crystals have to become electrically polarized when submitted to pressure or vice versa. In other words, it's the capacity of some materials to generate energy when squeezed or pressed.

One example is bioluminescence — the ability of certain marine organisms to naturally produce fluorescent light through a chemical reaction of certain proteins — or osmosis.

Beyond this piezoelectric effect or luminescent bacteria, we can also find innovation in construction materials that seek to be more energy efficient and sustainable. From concrete roofs and walls on buildings that absorb energy and transform it into electricity, to photovoltaic glass on a building that generates energy, there are so many options that open a world of possibilities for driving clean energy. 

But for the ordinary person, the world of electricity and, in general, of energy can seem quite complex. However, despite the many questions it may lead to, the concept of piezoelectricity is actually quite interesting. Even though it's true that the academic definition doesn't really begin to explain the topic to someone unfamiliar with the concept, in order to better understand it, we could say the term references the ability of some materials to generate electricity when subjected to mechanical stresses. The process also works inversely, where the actual materials are those that deform when subjected to an electrical field, but if the process is interrupted, they are able to return to their original state. 

Possible applications for piezoelectricity

distributed electricity generation in a smart city

Current examples of piezoelectricity

Did you know that electric lighters are a clear example of piezoelectricty? In this case, all you need to do is push a button so that the lever or hammer of the spring hits the piezoelectric crystals and, as a consequence of this mechanical stress, an electrical current is produced that travels as a flame to light the gas. 

Have you ever heard of a quartz watch? It's very likely you have. What you may not know is that it's another of the most common applications of quartz piezoelectricity. The different-sized quartz crystals vibrate at different velocities and produce electric pulses that the watch counts and measures in seconds, minutes, and hours. 

But not just that. We can find other examples of piezoelectric materials in our everyday life, such as in microphones, speakers, and headphones, which transform the electric waves into vibrations and these into sound or vice versa. Fuel injectors on combustion engines, pieces on an electric guitar, and even some ultrasound machines and sensors also use piezoelectricity.

People passing each other by

Until it was time to close down, at the Club Watt in Rotterdam, the Netherlands, the dance floor was powered by the electricity generated by the people who danced on it. This was also the case at the Natuur Café La Porte in Driebergen, The Netherlands, where piezoelectricity was applied to the revolving door system so when guests entered or left the building, they generated energy that later was used to light up the inside of the café..

Even the metro system in Tokyo has taken advantage of the passing of travelers. In this Japanese city, the steps taken by citizens over the metro system's piezoelectric tiles help supply the energy the stations need. 

For some time now, reality has exceeded our fictional imagination; and what was before unimaginable is now real life. And this is occurring with the application of piezoelectricity, a chapter that has significantly developed in the past few decades and that has provided some of the most ground-breaking results with more ideas that in the future could revolutionize the energy sector. 

Can you imagine walking through the supermarket and that the movement of the shopping cart is what generates enough electricity to light up the building? Or that the movement of the wheels on your car over the road lights up the road signs? And what if traffic lights were powered by the passing of pedestrians over crosswalks or around the city? A commitment to innovation is key for optimizing the uses of piezoelectric materials, and the research continues to advance, mainly by studying the possibilities of generating power from flows of traffic or people.

If we consider that the piezoelectric effect allows us to generate electricity for free just from movement — by transforming weight or friction into electricity — it's not hard to imagine the possibilities that infrastructure like the metro, roads, or sidewalks could offer in this sense. But, that's not all. In recent years, there have been a series of examples varying in size that use piezoelectricity on all types of surfaces.

Piezoelectricity in crystals

Main piezoelectric materials

Broadly speaking, two groups can be distinguished: those that possess this capacity naturally and those that exhibit piezoelectric properties once they have been subjected to polarization.

  • In the former group, quartz piezoelectricity is popular, but there are other piezoelectric crystals such as rubidium and tourmaline. 
  • In the latter group, we can find ferroelectric materials. Others such as lithium tantalum, berlinite in the form of monocrystalline materials, and even certain ceramics would also be included. 

As a matter of fact, although the term piezoelectricity and the identification of related materials can seem quite complex, it actually hides a multitude of somewhat everyday applications such as the ones mentioned above.