Remember ‘Wind Tree’, a miniature tree-shaped wind turbine designed by French company New Wind? A recent study, by scientists at Ohio State University’s Laboratory of Sound and Vibration Research, is somewhat along the same line, focusing on the development of a new technology that could convert tree movements into clean, usable energy. Based on piezoelectricity, the technique relies on the vibrations of trees in the wind, turning them into electricity.
Harvesting electrical power from materials subjected to mechanical stress or vibrations has been around for quite sometime now. As part of the new research, the scientists are developing high-tech objects that look like artificial trees and are actually capable of generating renewable energy when shaken by a gust of wind. Recently published in the Journal of Sound and Vibration, the study reveals that these tree-like structures, built using special electromechanical material, could successfully transform random forces, such as wind energy or even footfalls on a bridge, into powerful structural vibrations that can in turn produce electricity.
According to the researchers, tiny forests of artificial power-producing trees could one day prove valuable, especially in places where other renewable energy sources are not easily available. Possessing a trunk with a couple of branches and no leaves, this high-tech structure could be used to power sensors that check the structural integrity of buildings, bridges and other civil infrastructure. As the team points out, there is plenty of vibrational energy all around us, in the form of human activity-induced motions, wind-induced oscillations and even seismic activity. Speaking about the research, Ryan Harne, a professor of aerospace and mechanical engineering at Ohio State and the project’s leader, said:
Buildings sway ever so slightly in the wind, bridges oscillate when we drive on them and car suspensions absorb bumps in the road. In fact, there’s a massive amount of kinetic energy associated with those motions that is otherwise lost. We want to recover and recycle some of that energy.
At present, structural monitoring sensors run on batteries or power lines that directly feed voltage into the systems. Both, according to the scientists, are expensive and difficult to maintain, especially in remote locations. Thanks to the new technology, the sensors could soon be powered by the same vibrations they are recording. In the past, researchers have developed similar structures that can convert idealized vibrations into usable electricity. The new study marks the first time that scientists have been able to capture random ambient vibrations using special electromechanical devices.
Thanks to a phenomenon known as internal resonance, these artificial trees are capable of maintaining vibrations at a particular frequency, in spite of varying force inputs. This in turn ensures that the energy from the oscillations can be easily captured and stored for later use. With the help of mathematical modeling, the scientists learnt that internal resonance allows the tree-like device to vibrate at a consistent low frequency, when it is subjected to high frequency forces. The setup worked in much the same way, even when random noise was added to these forces.
For the experiment, the scientists built a miniature prototype using two steel beams and connecting them by means of strip of polyvinylidene flouride (PVDF), a material known for its electromechanical properties. When shook at high frequencies, the device appeared to oscillate at very low amplitudes. Nevertheless, it managed to generate around 0.8 volts of power. At low frequency motions, however, the contraption produced up to 2 volts. Harne added:
In addition, we introduced massive amounts of noise, and found that the saturation phenomenon is very robust, and the voltage output reliable. That wasn’t known before.
The research is still at its initial stages, and will likely take a while before the technology is available for commercial use.
Source: Ohio State University