Harvesting Energy From Nature's Motions

[Guest guest]

Harvesting Energy From Nature's Motions

http://www.medicalnewstoday.com/articles/169443.php

By taking advantage of the vagaries of the natural world, Duke University

engineers have developed a novel approach that they believe can more efficiently

harvest electricity from the motions of everyday life.

Energy harvesting is the process of converting one form of energy, such as

motion, into another form of energy, in this case electricity. Strategies range

from the development of massive wind farms to produce large amounts of

electricity to using the vibrations of walking to power small electronic

devices.

Although motion is an abundant source of energy, only limited success has been

achieved because the devices used only perform well over a narrow band of

frequencies. These so-called " linear " devices can work well, for example, if the

character of the motion is fairly constant, such as the cadence of a person

walking. However, as researchers point out, the pace of someone walking, as with

all environmental sources, changes over time and can vary widely.

" The ideal device would be one that could convert a range of vibrations instead

of just a narrow band, " said Stanton, graduate student in Duke's Pratt

School of Engineering, working in the laboratory of Mann, assistant

professor of mechanical engineering and materials sciences. The team, which

included undergraduate McGehee, published the results of their latest

experiments early online in Applied Physics Letters.

" Nature doesn't work in a single frequency, so we wanted to come up with a

device that would work over a broad range of frequencies, " Stanton said. " By

using magnets to 'tune' the bandwidth of the experimental device, we were able

verify in the lab that this new non-linear approach can outperform conventional

linear devices. "

Although the device they constructed looks deceptively simple, it was able to

prove the team's theories on a small scale. It is basically a small cantilever,

several inches long and a quarter inch wide, with an end magnet that interacts

with nearby magnets. The cantilever base itself is made of a piezoelectric

material, which has the unique property of releasing electrical voltage when it

is strained.

The key to the new approach involved placing moveable magnets of opposing poles

on either side of the magnet at the end of the cantilever arm. By changing the

distance of the moveable magnets, the researchers were able to " tune " the

interactions of the system with its environment, and thus produce electricity

over a broader spectrum of frequencies.

" These results suggest to us that this non-linear approach could harvest more of

the frequencies from the same ambient vibrations, " Mann said. " More importantly,

being able to capture more of the bandwidth makes it more likely that these

types of devices could someday rival batteries as a portable power source. "

The range of applications for non-linear energy harvesters varies widely. For

example, Mann is working on a project that would use the motion of ocean waves

to power an array of sensors that would be carried inside ocean buoys.

" These non-linear systems are self-sustaining, so they are ideal for any

electrical device that needs batteries and is in a location that is difficult to

access, " Mann said.

For example, the motion of walking could provide enough electricity to power an

implanted device, such as a pacemaker or cardiac defibrillator. On a larger

scale, sensors in the environment or spacecraft could be powered by the everyday

natural vibrations around them, Mann said.

Mann's research is supported by the Office of Naval Research.