Harvesting Electricity from Motions of Everyday Life
By capitalizing on the vagaries of the natural world, Duke University engineers have produced a new approach that they believe can more efficiently harvest electrical energy from the movements of everyday life.
Energy harvesting is the process of changing one form of energy, such as motion, into another form of energy, in this case electrical energy. Strategies range from the exploitation of massive wind parks to produce large quantities of electrical energy to using the vibrations of walking to power small electronic devices.
Whilst motion is an extensive source of energy, only limited success has been accomplished because the devices used only perform well over a narrow band of frequencies. These supposed “linear” devices can work well, for instance, if the character of the movement is fairly unceasing, such as the measure 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 Samuel Stanton, graduate student in Duke’s Pratt School of Engineering, working in the laboratory of Brian Mann, assistant professor of mechanical engineering and materials sciences.
Future of Electrical Energy Storage
“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 established linear devices.”
Whilst the device they constructed looks deceivingly 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 therefore create electrical energy over a wider spectrum of frequencies.
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