Piezoelectric scheme seeks to reap the wind while driving

PORTLAND, Ore. — Piezoelectric wind harvesters mounted on vehicles could generate electricity to charge batteries or power on-board electronics while simultaneously decreasing drag caused by vibrations, according to a researcher.

Piezoelectric modules developed by City College of New York professor Yiannis Andreopoulos alone would generate only milliwatts today. But since current output is proportional to velocity, the wind harvesters could potentially generate thousands of watts of power if mounted on vehicles or even airplanes.

Piezoelectric energy harvesters vibrate in air flows to generate electricity that can be used to charge batteries or to power on-board electronics. Click on image to enlarge.

"Right now we can only generate milliwatts per square meter in our wind tunnel, but we can increase that by optimizing the electrical circuit," said Andreopoulos. "We possibly can anticipate 1,000 times more, [or] 200 watts per square meter. However we plan to design this device for an airliner, which fly about three times faster."

Since the energy produced is proportional to the cube of velocity, an airplane flying at 450 mph would boost the power output of a piezoelectric module by about nine times greater than current tests in a 150-mile-per-hour wind tunnel. By switching to a stiffer piezoelectric material with a coefficient 10 times higher, the power generated could potentially be boosted to as much as 18,000 watts per square meter.

The generators use arrays of piezoelectric modules measuring about 30 by 20 by 0.2 mm. The substrate is a mylar-based plastic with the piezoelectric material just 18 microns in thickness on the top. Rather than locating modules on smooth surfaces, where they might create drag, they could instead be installed as splitter plates on top of or at the rear of a vehicle where they could harvest vibrations while simultaneously lowering the drag on the vehicle by quelling turbulence.

"When you put it into the wake of a cylinder, it acts like a splitter plate that reduces the drag of the cylinder itself," said Andreopoulos.

His team verified its simulation results in the wind tunnel where a beam resonated at the frequency of its maximum output by harnessing pressure from vortices on the turbulent side of the piezoelectric beam. The beam was balanced against low pressure regions created on the opposite side.