Convert Stress into Electricity: Piezoelectricity

Convert Stress into Electricity: Piezoelectricity

by Nethma Dissanayake

Have you ever heard about electricity generating materials? If not, you’re lucky to find this article which explore the wonders of materials science. Imagine how valuable it is if your footsteps could power lights in the dark. Interestingly, a certain type of materials called “Piezoelectric materials” have a specific ability to store energy when a mechanical stress is applied. The word piezoelectricity referred to the resultant electricity generated from pressure and latent heat. Discovery of these materials date back to 1880, when French physicists Jacques and Pierre Curie were working at the faculty of science in Paris. Investigation of piezoelectricity was focused as a new research field in 19th century which had led to innovate piezoelectric oscillator, ultrasonic submarine detector, and Rochelle salt microphone cable using piezoelectric materials.

As previously mentioned, piezoelectricity is generated from the pressure applied on piezoelectric materials. In general, positive, and negative charges are symmetrically distributed in a piezoelectric material. Then DC voltage across material is induced (poling). It is noteworthy that polarization remains even after the outward pressure is removed. During the stage where a mechanical force is being applied to the material, a negative charge is produced on the expanded side whereas a positive charge is created on the compressed side. Once the pressure is relieved, electrical current flows across the material. This is the simple mechanism of generating piezoelectricity. On the other hand, the piezoelectric effect of a material can be reversed as well. Accordingly, a mechanical strain is internally generated because of the applied electric field. Quartz, rochelle salt, topaz, silk, dentin, DNA, and tendon are some natural sources of piezoelectric materials. Lead zirconate titanate (PZT), Zinc oxide (ZnO), Barium titanate, Lead titanate, Langasite, Sodium tungstate, and Potassium niobate are synthetically produced.

Let’s look at the current state and latest trends of piezoelectricity in the world. Global “Piezoelectric Devices Market” report evaluates data related to industries and markets, abilities and technology, risks, and challenges. It forecasts that the global market size of piezoelectric devices will reach USD 35.4 billion in 2026 (Market Research Report, 2021). Meanwhile, applications of piezoelectricity expand drastically to be able to align with the smart world. Some amazing applications of piezoelectric materials in the world are piezoelectric based tennis racquets, monitoring changes in the vibration behavior of wheels, crystal laid down under keys of mobile units and keyboards (when pressed vibrations are created, it can be used for charging process), sensors, power generating shoes, and energy harvesting streets tiles. Some countries are trying to construct charging pads under pedestrian crosswalks to collect energy from the vibrations which is then utilized to charge lithium-ion batteries. In some airports where piezoelectric technology has been implemented, a tendency can be seen among passengers to jump or walk on charging pads to generate electricity for fun. Even though the generated electricity is relatively small, this method is eco-friendly, and many people are being encouraged to actively contribute to power generation.

Electricity generating tiles developed on roads

Interestingly, piezoelectric materials have gained a considerable attraction among researchers. At microscopic scale, piezoelectric materials contain domains that are separated by domain walls. One of the key research areas of piezoelectricity is to reduce domain size of the piezoelectric material to improve piezoelectric performance. Noticeably, there are only a few materials that have been modified to generate piezoelectricity. Investigation of novel materials which are low cost and have a high piezoelectric coefficient will be a turning point in the field to overcome current challenges. Incorporation of eco-friendly aspects would also increase the demand for piezoelectric materials in various industries