by Anurag Sritharan
When we walk or dance we put pressure on the ground in the opposite direction (backwards) to move in the direction we want. The energy (due to pressure) used while walking is completely wasted, but, could we harness that pressure to create useful energy? Demonstrated in 1880 by renowned French physicists Pierre Curie and Paul Jacques Curie, Piezoelectricity had started to gain attention during The World War when it was used to make sonar devices for submarines. But, towards the 1990s the effect has been used in a variety of common social interactions to power street lights and LED’s. In 2008, club Surya in London became one of the first clubs to feature piezoelectric dance floor through which the whole club was powered from lights to sound. How can such tiny crystals produce enough electricity to power a club? Let’s dive into its matrix!
The pyroelectric effect, by which a material generates an electric potential in response to a temperature change, was studied by Carl Linnaeus and Franz Aepinus in the mid-18th century. Working on these lines René Just Haüy and Antoine César Becquerel found a relationship between mechanical stress and electric charge but were not able to demonstrate it. In 1880 the Curie brothers demonstrated this relationship with crystals of tourmaline, quartz, topaz, cane sugar, and Rochelle salt (sodium potassium tartrate tetrahydrate).However, it took another year to prove the effect mathematically and was done by a physicist from Luxemburg named Gabriel Lippmann. This marked the final step before integrating it into applications such as sonar technologies in WW1.
To understand how this works we first have to understand the pyroelectric force. “The pyroelectric effect has been known for 24 centuries—the Greek philosopher Theophrastus probably wrote the earliest known account. He described a stone, called lyngourion(picture to the right) in Greek or lyncurium in Latin, that had the property of attracting straws and bits of wood. Those attractions were no doubt the effects of electrostatic charges produced by temperature changes most probably in the mineral tourmaline.”(Pyroelectricity).
The piezoelectric effect is not caused due to a change in temperature rather a change mechanical stress. Piezo in Greek translates to push. In general terms the crystals give off electricity if we hit them with a hammer or squeeze and stretch them out. Why does this exactly happen? This comes down to the lattice arrangement of different atoms/compounds of the material. Let’s take a look at the picture below
The picture shows 3 arrangements of quartz: no stress, tension and compression. We see that the lattice structure or how the atoms bond together are different in each case. When there is no stress it forms a nice hexagon. When there is a force of tension applied to the crystal the hexagon elongates this causes energy (mostly electrical) to build up in the bonds. This build up happens due to the shifting of electrons that are shared between the atoms which could move to one side causing a high potential to build up in the crystal. When it is compressed the charged particles (electrons) move to a different part of the crystal rapidly and thus electric current is produced by the rapid movement of electrons. High voltages can be produced with enough material and could also cause sparks.
The first application of piezoelectric crystals was in sonar. Let us see how this worked. When the sound pressure is release through a microphone it hits the surface of an object and reflects off the surface. When it comes back to the ship a microphone amplifies the reflected sound and this is carried into a chamber with a piezoelectric crystal, the sound pressure causes a mechanical stress point which activates the crystal and a small voltage is picked up. The device then calculates the distance using the time gap between when the sound was emitted and when the voltage spiked. (PZT is the piezoelectric crystal)
Quartz is another well-known piezoelectric crystal, “the most widely known application is the electric cigarette lighter: pressing the button causes a spring-loaded hammer to hit a piezoelectric crystal, producing a sufficiently high-voltage electric current that flows across a small spark gap” (Alchemy). Another well know application is “a quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time.” (Alchemy) quartz isn’t the only piezoelectric crystal. Bones, DNA, ceramic and even sugar have been known to create electricity through this effect.
We can thus use these materials to power led lights or disco as dancing and walking causes high amounts of mechanical stress or pressure being applied in the downward direction. “The piezoelectric dance floors installed in London's Club Surya, an eco-nightclub launched in July 2008, and Rotterdam's Wvatt, a sustainable dance club launched in September 2008. The clubs' dance floors are engineered with springs and series of crystal and ceramic blocks. When patrons at each club dance, the pressure they exert on these blocks causes the dance floor to depress slightly and the blocks to rub against each other. The result is the generation of a small electric current. This process effectively captures the dancers' kinetic energy, and feeds it into nearby batteries. In Club Surya, for instance, batteries power the club's lights and air conditioning, and supply up to approximately 60 percent of the club's energy needs.” (Kim) In Japan, Tokyo, the floors of the ticket gate in Tokyo station are lined with piezoelectric crystals providing lighting and enough energy for the ticket gates to work. I would like to share a small news clipping from the Japan Times “In an effort to make train stations in the national Japanese railway network more energy efficient, the East Japan Railway Company (JR East) worked in conjunction with researchers from Keio University to embed piezoelectric pads in the floors under the ticket gates in Tokyo Station.”
Piezoelectric motors are also another common use. The possibilities for this effect are endless and could possibly be a solution to global warming. Imagine streets that are filled with piezoelectric crystals that provide electricity for street and traffic lights, all one has to do is walk on the roads a simple push that might save humanity.
Work Cited
1. Pyroelectricity: From Ancient Curiosity to Modern Imaging Tool. (n.d.). Retrieved August 8, 2020, from https://www.slac.stanford.edu/grp/arb/tn/arbvol5/AARD459.pdf
2. Alchemy Technology. (n.d.). Piezoelectric effect. Retrieved August 08, 2020, from https://alchemytechnology.org/f/piezoelectric-effect
3. Author Profile, Kim Diamond Vice Chair of the Carbon and Energy Trading and Finance Committee, Diamond, K., Vice Chair of the Carbon and Energy Trading and Finance Committee, Follow Contact, About meKimberly E. Diamond is a Vice Chair of the Carbon and Energy Trading and Finance Committee of the American Bar Association's Section of Environment, . . . 28, R. (n.d.). Breakthroughs in Piezoelectric Power: Raising Public Awareness is a Step in the Right Direction for U.S. Sustainable Development. Retrieved August 08, 2020, from https://energycentral.com/c/um/breakthroughs-piezoelectric-power-raising-public-awareness-step-right-direction
Photos
1. 1. Alchemy Technology. (n.d.). Piezoelectric effect. Retrieved August 08, 2020, from https://alchemytechnology.org/f/piezoelectric-effect
2. (n.d.). Retrieved August 08, 2020, from https://www.electronicdesign.com/power-management/article/21801833/what-is-the-piezoelectric-effect
3. Healing, S. (2015, December 10). Lyngourion. Retrieved August 08, 2020, from https://suravanihealing.wordpress.com/tag/lyngourion/
4. Dancefloor generates electricity at London's first eco-disco! (n.d.). Retrieved August 08, 2020, from https://inhabitat.com/green-a-go-go-at-londons-first-eco-disco/
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