Researchers in the Lyles School find new ways to harness wasted energy

Na (Luna) Lu, associate professor of civil engineering, leads two teams in separate but connected research endeavors. The first involves developing cost-effective thermoelectric materials and systems for civil infrastructure applications. The second involves developing high-performance piezoelectric sensors for nondestructive testing and structural health monitoring.

Simply put: Lu's team is researching how to create reliable, effective devices that can convert heat and vibrations into electricity.

“We are developing these to be low-cost, high-performance devices to power the future,” Lu says. “We are very excited with the work we have done so far.”

Lu explains that as much as 60 percent of the energy produced in the United States is wasted as a form of heat, which could be directly converted into electricity using cost-effective thermoelectric materials. As such, thermoelectric materials offer great promise for energy-efficient power generation in civil infrastructures, by recovering wasted heat from HVAC systems and building envelopes, for instance.

However, Lu says, the potential impact of thermoelectric materials is greatly hindered by the heavy use of toxic, rare and expensive elements necessary to manufacture them. Through a National Science Foundation CAREER Program grant, Purdue Civil Engineering’s Sustainable Materials and Renewable Technology (SMART) Lab has developed nanostructured oxides and nitrides as promising, cost-effective materials to
overcome this challenge due to their favorable properties and earth abundance.

On the piezoelectric side of Lu’s research, her team is working to create devices that can directly convert mechanical vibration into electrical energy and vice versa. This reciprocal energy conversion effect of piezoelectric materials enables them to be used as sensors, transducers, actuators and power sources. “The issue in the past with this kind of research has been that the ceramic materials typically used are too brittle and can be toxic,” says Ehsan Ghafari, civil engineering PhD student. “We needed to fi nd a new material that could be flexible, safe and inexpensive.”

The SMART Lab’s answer is the polymer material polyvinylidene fluoride (PVDF). PVDF can be used to create lightweight, high-performance and low-cost piezoelectric devices that can be mounted on civil infrastructures for energy harvesting, nondestructive testing and structural health monitoring.

Lu says these piezoelectric sensors potentially could be used to monitor concrete properties to determine the optimal traffic times around a construction site via the vibration absorbed from passing vehicles. Similarly, these PVDF-based piezoelectric sensors can be used for in situ monitoring of bridge deflection, pavement cracking, de-bonding, corrosion and other damage.

“The uses for these devices are really promising,” Lu says. “The sustainable energy from both materials could completely change how future cities are powered. It’s an exciting prospect.”