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 November 18, 2009
Harvesting Ambient Energy from Nature

 We all know that energy can neither be created nor be destroyed but can only be transformed into one form to another. Duke University engineers are trying to utilize this simple formula. They are working on harvesting energy from the motions of everyday life. Normally our everyday motions get wasted and remain unused and dissipate in the form of heat without our realization. Energy harvesting strategies cover the installation of colossal wind farms to manufacture large amounts of electricity to using the vibrations of walking to power small electronic devices.

We have not estimated the exact amount of energy generated by random movements of our daily life. But it is indisputable that the trapped day-to-day motions can be a source of huge energy. But right now only limited success has been achieved because the devices used perform well only over a narrow band of frequencies. These devices have certain limitations. They perform well only when forces of motions are fairly constant. If we take an example of walking it is clear that we can't walk at a constant pace. There are some external environmental forces working. So accordingly our pace of walking changes and varies too.

Samuel Stanton, who is a graduate student in Duke's Pratt School of Engineering, and working in the laboratory of Brian Mann, assistant professor of mechanical engineering and materials sciences, says, "The ideal device would be one that could convert a range of vibrations instead of just a narrow band. 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. 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."

Their device looks quite simple in appearance. But it is sufficient to prove their theory and mode of working. The device is mainly a small cantilever. This cantilever is many inches long and a quarter inch wide. It also has an end magnet that interacts with nearby magnets. The cantilever base consists of a piezoelectric material. This piezoelectric material has the exceptional property of releasing electrical voltage when it is strained.

They devised a means to place movable magnets of opposing poles on either side of the magnet at the end of the cantilever arm. This arrangement is important because by changing the distance of the movable magnets, they were able to "tune" the interactions of the system with its environment. This tuning will help in trapping and producing electricity over an erratic range of frequencies which is of normal occurrence of daily life.

The range of applications for non-linear energy harvesters is only restrained by our imagination! Mann is aiming to achieve how to use the motion of ocean waves to power an array of sensors that would be carried inside ocean buoys. Mann shares the benefits with us, "These results suggest to us that this non-linear approach could harvest more of the frequencies from the same ambient vibrations. 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."

Mann is of the view, "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." If we go by the example of our walking, the motion of walking is sufficient to provide enough electricity to operate an implanted device, such as a pacemaker or cardiac defibrillator. If we take some bigger example we can observe, scale, sensors in the environment or spacecraft could be power-driven by the everyday natural vibrations around them.