Research Stories

by Joe Kullman

In dance and stage choreography they call it economy of movement—getting the optimal theatrical value out of whatever energy you expend. The goal: No wasted motion.

Henry Sodano's work involves a kind of mechanical engineering application of that pursuit of kinesthetic efficiency.

The assistant professor in the Department Mechanical and Aerospace Engineering in the Ira A. Fulton School of Engineering is advancing technologies for "energy harvesting."

One of his forays into the field demonstrates a particularly economical and practical way to generate small but useful amounts of electrical power.

He has designed a backpack using material capable of producing an electrical charge through the force of the motion of its wearer.

Through the conductive capability of the material, friction caused by the movement of the backpack wearer is converted into electrical energy, enough to charge small batteries or power small electronics devices such as cell phones, iPods or flashlights.

The backpack's shoulder straps are made of a polymer—polyvinylidene fluoride (PVDF)—a flexible material with properties similar to nylon. PVDF makes the straps piezoelectric, meaning they are able to generate and transfer an electrical charge when force or pressure is applied to them.

"Your normal gait causes the backpack to move up and down during each step, resulting in a force in the pack's straps," Sodano explains. "The piezoelectric material used for the strap has the ability to transform this alternating force into electrical energy that can be collected and used to power an electronic device."

The process is a simple and efficient way for using otherwise wasted energy from physical movement by converting it into electricity.

Sodano conducted the research behind the power-generating backpack with support from the Office of Naval Research, which is looking for alternative power sources for Marines in the field.

What Sodano has in mind to do eventually is apply the technology for military purposes to reduce the loads carried by soldiers, allowing them to operate more efficiently and safely. The backpack straps may also be used as supplemental energy sources for handheld Global Positioning System (GPS) units or night-vision goggles.

The concept of energy harvesting could, for instance, also be applied to sensors to monitor the structural stability of bridges by converting the energy generated by the vibrations from automobiles driven across bridges to electrical power.

"There's a lot of energy in your body that could be converted into electrical energy," Sodano says. "Your heartbeat could provide energy to help power a pacemaker. You could even use the energy produced by the expansion and contraction of your rib cage as you breathe."

Help developing the backpack concept came from graduate students at Michigan Technological University, where Sodano taught before coming to ASU in August, and from NanoSonic Inc. The high-tech company produced the nanostructured electrodes that allows the straps to withstand the rigors of everyday use.

Sodano is now organizing a special energy-harvesting issue of Journal of Intelligent Material Systems and Structures.

He hopes to attract additional funding for his research to develop more advanced prototypes of energy harvesting methods and commercialize them.

For more information about engineering research at ASU, visit the Ira A. Fulton School of Engineering news page at: http://www.fulton.asu.edu/fulton/news/