Research Magazine 2006
Shashank Priya
If we can learn to convert this mechanical energy into electrical energy with high efficiency, then it will be sufficient to power the mobile devices. Piezoelectric materials provide that interface between the mechanical world and the electrical world.

Energy efficient

Landmine detection, robot tutors and cellphone batteries are among potential applications for professorís piezoelectric power harvesting

The cube-shaped structures Shashank Priya uses to teach his students look a lot like Tinker Toys.

In fact, Dr. Priya says with a smile, his 2-year-old daughter, Prabha, often plays with the red, white and black spheres at the feet of her father while he does his trendsetting work in piezoelectric energy harvesting.

Derived from the Greek piezein, which means to squeeze or press, piezoelectric (generating electricity from mechanical forces and vice versa) applications abound, explains the assistant professor. “We use piezoelectric applications every day. You just don’t know it.”

Take today’s gas grills or stoves. Pressing a button causes a spring-loaded hammer to hit a piezoelectric crystal, and the voltage produced ignites the gas as the current jumps over a small spark gap. Similarly, the light that brightens your laptop computer uses piezoelectric transformers.

Piezoelectricity has worked behind the scenes in sonar devices for years. Go back a few thousand years, and piezoelectricity benefited the Uncompahgre Ute Indians, historians say. Using quartz crystals, the Utes made buffalo-skin rattles that, when shaken, created friction and mechanical stress between the crystals, thus producing flashes of light.

The Utes valued the rattles as powerful religious objects. Fast-forward to Priya’s Materials Science and Engineering Department office, and the 30-year-old mathematician will tell you he considers them to be the next big thing: from landmine detection, to robots exhibiting lifelike facial expressions, to batteries for cellphones.

Nokia researchers are among those who are listening to Priya. For the past several years, he and his team of graduate students and others have studied ways to create a piezoelectric battery for cellphones using mechanical energy harvesting. Priya believes a solution is near.

“The best way to think about piezoelectric materials,” he begins, “is to realize that they work in two ways. When a piezoelectric material is squeezed, the electric charge is generated across the material. Or when electric voltage is applied on the piezoelectric material, it deforms.”

Many crystalline materials exhibit piezoelectric behavior, including quartz, barium titanate, zinc oxide and other ceramics.

How would a piezoelectric battery in a cellphone work? Good question, Priya says, especially when you consider that walking dissipates large amounts of mechanical energy. Even moving a finger exerts energy.

“If we can learn to convert this mechanical energy into electrical energy with high efficiency, then it will be sufficient to power the mobile devices,” he said. “Piezoelectric materials provide that interface between the mechanical world and electrical world.”

Users of future-tech phones could one day power such a device by rubbing its casing, Priya believes. This would generate a small electrical charge, enough to make a short call.

He points to a cellphone on his desk.

“The plastic in this phone is dumb plastic; if I rub it, it does nothing. What we’re investigating is flexible piezoelectric materials that would generate electricity for the phone.”

Nokia senior research manager Ramin Vatanparast finds Priya’s results encouraging but far from application. “We hope in the next step to see the application of the work happening at UT Arlington.

“We have been impressed by Priya and his depth of knowledge. We learned about his research at a presentation, and that led to an open and fruitful conversation, creating the opportunity for the current project.”

Priya and his research colleagues have also created two versions of inexpensive piezoelectric generators that use air movement to produce power. A breeze as small as that created by a phone moving through the air is enough to generate 5-50 microwatts, at a cost of less than $10. Considering the cost of today’s batteries, that’s a pretty good deal. Priya envisions similar applications for everything from insulin pumps powered by heart vibrations to radios powered by the simple act of walking.

“Our research is mature now,” he says with quiet confidence. “We just need to translate that to industry.”

And that’s just the beginning.

In conjunction with UT Arlington’s Automation & Robotics Research Institute, Priya is exploring how piezoelectricity can animate a robot’s face well enough to not only tutor children, but capture their imagination. Considering that this facial “skin” is thinner than a human air, it’s a perfect application of piezoelectricity.

“They are very human-like,” Priya says of the robots. “We’ve implemented piezoactuators that respond to changes in the skin of the robot. We’ve implanted motors inside the head that generate strain, which deforms the skin, creating expressions, such as a smile.” The work is funded by the National Science Foundation through a Small Business Technology Transfer grant with Hanson Robotics.

Another application in the works is a research grant examining whether piezoelectric sensors could be used for landmine detection vehicles currently deployed in Iraq.

Armed with an education in math and physics, Priya has always been “driven by how things behave.” He earned a master’s degree in metallurgy from the Indian Institute of Science, one of his native country’s top schools, and a Ph.D. from Pennsylvania State University.

“I became interested [at Penn State] in pattern recognition systems, or how people do things and behave. I wondered if it was possible to calculate that mathematically. That helped me a lot with the research I do now.”

What the future holds for piezoelectricity and its use in cellphones, robot tutors and other areas is uncertain, but Priya remains optimistic. As he and his wife raise their daughter, Priya reflects on the way the youngster plays with his piezoelectric models.

And he realizes his livelihood involves doing what he himself has loved since his own Tinker Toy days.

— David Van Meter