Wringing more energy out of everyday motions

Feb 21, 2012

Randomness and chaos in nature, as it turns out, can be a good thing – especially if you are trying to harvest energy from the movements of everyday activities like walking.

Duke University engineers believe they have come up with the theoretical underpinning that could lead to the development of harvesting devices that are not only more versatile than those in use today, but should be able to wring out more electricity from the motions of life.

Energy harvesting is the process of converting one form of energy, such as motion, into another form of energy, in this case electricity. Typically, energy harvesters make use of a piezoelectric material, which is usually a man-made laminate that produces small amounts of electricity when stressed or strained.

For example, the motion of walking could provide enough electricity to power a cell phone or an implanted device, such as a pacemaker or cardiac defibrillator. The Duke team is investigating whether such nonlinear devices could power sensors on buoys by extracting electricity from the motions of waves. Or on a larger scale, perhaps a series of nonlinear devices working together could generate enough electricity to power even larger devices.

However, current energy harvesting devices have been unable to efficiently make this energy conversion because the devices can only be "tuned" to a single frequency, or size of vibration. These so-called "linear" devices work well, for example, if the wind blows at a constant predetermined speed or a person walks at a steady pace.

"We know that in the real world, however, there can be so many variables that a traditional linear harvester would only be able to take advantage of a very limited frequency," said Benjamin Owens, a graduate student working in the laboratory of senior researcher Brian Mann, associate professor of mechanical engineering and materials science at Duke's Pratt School of Engineering.

The results of the team's research were published on-line on the journal Physica D: Nonlinear Phenomena. The researchers are supported by Army Research Office and the Office of Naval Research.

Mann said that linear energy harvesters will always work well in a laboratory setting, for example, since variables can be tightly controlled. He said that the mathematics involved in designing and measuring the efficiency of energy harvesters in a controlled environment is relatively straightforward and well understood by scientists.

Until now, the traditional formulas and equations used in designing linear devices could not be applied to the wide variety of frequencies encountered in real life. The Duke engineers reworked the principles commonly used for linear devices to take into account a greater range of frequencies, which would make such "nonlinear" devices able to harvest more energy.

"This nonlinear approach offers significant improvements in electricity production, sometimes on the order of one magnitude," Mann said. "Our approach for studying energy harvester performances provides a simplified method for design and analysis of nonlinear systems."

The researchers used magnets to simulate nonlinearity in a cantilever model made of a piezoelectric material, which has unique property of releasing energy every time it is bent. By changing the orientation of the magnet, the researchers were able to "tune" the bending of the arm, and thus the production of , over a broader spectrum of frequencies.

"These results suggest to us that this nonlinear approach could harvest more of the frequencies from the same ambient vibrations," Mann said. "More importantly, being able to capture more of the bandwidth would make it more likely that these types of devices would have practical uses in the real world. These nonlinear systems are self-sustaining, so they are ideal for any electrical device that needs batteries or is in a location difficult to access."

Samuel Stanton, who graduated last year, is a co-author of the paper.

Explore further: Lifting the brakes on fuel efficiency

Related Stories

Good vibrations

Mar 23, 2010

(PhysOrg.com) -- Energy harvesting - using vibrations from the environment to produce electricity - has been around for over a decade, but Dr Stephen Burrow and his team in the Department of Aerospace Engineering at the University ...

Recommended for you

Lifting the brakes on fuel efficiency

19 hours ago

The work of a research leader at Michigan Technological University is attracting attention from Michigan's Governor as well as automotive companies around the world. Xiaodi "Scott" Huang of Michigan Tech's ...

Large streams of data warn cars, banks and oil drillers

Apr 16, 2014

Better warning systems that alert motorists to a collision, make banks aware of the risk of losses on bad customers, and tell oil companies about potential problems with new drilling. This is the aim of AMIDST, the EU project ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

jimbo92107
not rated yet Feb 21, 2012
Paging Mr. Fibonacci. Sounds like a dendritic phenomenon, branching and turning like a tree to capture motion energy as it passes from one size regime to another. Not just efficient, but pretty, too.
antialias_physorg
not rated yet Feb 22, 2012
Paging Mr. Fibonacci

More like prime numbers. You'd want to tune these multivariate energy harvesting devices to frequencies that aren't harmonics of other frequncie you're harvesting.

More news stories

Researchers uncover likely creator of Bitcoin

The primary author of the celebrated Bitcoin paper, and therefore probable creator of Bitcoin, is most likely Nick Szabo, a blogger and former George Washington University law professor, according to students ...

LinkedIn membership hits 300 million

The career-focused social network LinkedIn announced Friday it has 300 million members, with more than half the total outside the United States.

Impact glass stores biodata for millions of years

(Phys.org) —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...