Durham, N.C. UK. — If you are trying to obtain energy from everyday moments movements like walking, then randomness and pure chaos can be a positive thing.
The engineers at Duke University believe they have discovered a support system that could lead to energy harvesting devices that are more advanced than the ones currently in use. They should also be able to emit more electricity from life’s daily motions.
Energy harvesting means the process of converting one form of energy into another form, electricity in this situation. Energy harvesters use a man-made laminate that produces small amounts of electricity when strained.
Walking motion could provide enough energy to power a mobile device, and medical devices such as a pacemaker. The team at Duke is investigating whether these devices could emit power by extracting electricity from wave motions or if nonlinear devices together could generate enough electricity to power even larger devices
Current energy harvesting devices have been unable to make this energy conversion because the device can only be tuned to a single frequency or vibration size. The “linear” devices work well, in that if the wind blows at a consistent velocity or a person walks at an average 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 Duke’s research were published at the online 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.”
Recently, traditional formulas and equations that are used in designing linear gadgets could not be utilized for the wide variety of frequencies for everyday life. The researchers at Duke studied the principles used for linear devices to obtain a greater range of frequencies, which would make nonlinear devices able to harvest 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 location of the magnet, the researchers were able to “tune” the bending of the arm, and the production of electricity, 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.”
