Canopy Club

OSU developing electromechanical trees to capture energy

For all the times we’ve looked to the breeze in the trees for answers – here’s the payoff.

Development of electromechanical trees for renewable energy harvesting is on the horizon.

Development of electromechanical trees for renewable energy harvesting is on the horizon.

Researchers at Ohio State University have begun developing methods of harvesting previously wasted energy with electromechanical devices in tree-shaped form. The project is designed to test whether these mechanisms are capable of generating renewable power when shaken by various oscillations; a breeze of wind being the most simplistic, all the way up to movements including the swaying that occurs with skyscrapers, traffic that causes bridges to vibrate, and seismic activity.

The root – or trunk – of this discovery came from an issue of the Journal of Sound and Vibration dated February 17th, but which includes an abstract released earlier in the month. In the journal, researchers report findings in tree-like structures made with electromechanical materials that can convert random forces into strong structural vibrations with potential for generating electricity. Basics for this concept have been explored before, such as in Paris in 2014, mainly for aesthetic purposes. This tutorial is helpful, if you don’t mind robot narration:

Creating devices with the relative shape of trees to capture wind or vibration energies has been deemed useful research because trees dissipate energy when they waver in a breeze. However, such demonstrations have involved “idealized” vibrations, which are programmed and not random. This isn’t realistic for structures intended for large quantities of renewable energy generation, because they would be experiencing constant random fluctuations in the wind or vibration impact. It was previously concurred that such forces wouldn’t be suitable for generating consistent enough oscillations to yield a useful amount of electrical energy.

Assistant professor of mechanical and aerospace engineering and director of the Laboratory of Sound and Vibration Research Ryan Harne spearheaded the project. He determined that it is possible for tree-like structures to maintain vibrations at a consistent frequency despite large, random inputs, allowing energy to be captured and stored through power circuitry. This process is called internal resonance, which Harne used as a way of extracting vibrations with large amplitudes, but at a low frequency, from the electromechanical trees, even when only high frequency forces were being employed. It continued to be effective when separate random noises were added, which would likely occur in many natural environments where the structures would be installed.

The trees were built using two small steel beams, one each for a makeshift trunk and branch. These were connected by a strip of polyvinylidene fluoride (PVDF) an electromechanical material apt at converting the oscillations into energy.

After shaking the tree back and forth at a range of frequencies, the PVDF produced a small voltage from the motion: about 0.8 volts. Then they added noise to the system, as if the tree were being randomly nudged slightly more one way or the other. That’s when the tree began displaying what Harne called “saturation phenomena”: It reached a tipping point where the high frequency energy was suddenly channeled into a low frequency oscillation. At this point, the tree swayed noticeably back and forth, with the trunk and branch vibrating in sync. This low frequency motion produced more than double the voltage—around 2 volts. These are low voltages, but enough for proof that random energies can produce vibrations that are useful for generating electricity.

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