There's a lion's share of potential energy in the vibrations produced by footsteps on dance floors, exercise machines in the gym, or the engines of cars, planes or construction equipment. Some tech companies have already begun to harvest electricity from waste vibrations to power lights and recharge batteries using a class of piezoelectric ceramic materials, which emit electrical charges when stepped on or manipulated.
Now, a team led by materials scientists at Penn State has expanded these early efforts of energy harvesting by improving the structure and chemistry of a piezoelectric material made of potassium sodium niobate, or KNN. The improved ceramic samples are thermally stable, fatigue resistant, less dense and perform competitively to existing lead-based piezoelectric materials, the researchers said.
Their work, which was published in the journal Small, could help replace toxic lead-based materials currently used in piezoelectric materials, the team said.
"Mechanical vibrations are everywhere, produced by people or engines," said first author Aman Nanda, a doctoral student in materials science and engineering at Penn State. "We can place a piezoelectric energy harvester under dance floors and corridors, or under bridges and parking decks, to harvest the energy from those mechanical sources. Because of the lightweight design of our KNN material, we could also include them in aircraft - which wasn't previously possible with lead-based materials - to harvest the vibrations during flights, even at high altitudes."
Energy harvesters have a cantilever design, where a stiff element is fixed on one end and unattached on the other, Nanda explained. Since ceramic materials are brittle, special care and device designs are needed to apply them in real applications to handle mechanical stress.
When pressed, the cantilever vibrates and generates electricity through the piezoelectric effect of the material that converts mechanical energy into power.
To replace lead and produce a more lightweight piezoelectric ceramic, the researchers systematically modified the structure and chemistry of KNN. They first added a magnetic material, manganese, to its chemical composition. Then they adjusted the grain growth, or the size of individual crystals within the microstructure, through heat treatment.
