Think about some windmills that look a lot like trees but generating energies when they move in the breeze. Sounds amazing, right? A team of engineers at Ohio State University are working on tools to harvest energy from air which may look more like tiny lifeless trees rather than giant windmills.
In a recent publish of the Journal of Sound and Vibration, scientists claim that they have revealed something new about the resonances that pass through tree-shaped objects while they are shaking. From that report, they’ve argued specifically that objects that look like artificial trees with electromechanical materials are able to convert random forces, such as winds or steps on a bridge – into structural vibrations, ideal to generate electricity.
This idea may produce images of fields full of artificial trees swaying in the breeze in your mind. However, project leader Ryan Harne hopes after applying on a small scale, the project may prove most worthy, in a situation where renewable energy sources like solar systems are not options. The so called trees won’t have any complex structures; just think of a trunk with a few branches and without leaves.
In the early applications, powering the sensors to monitor the structural integrity and health of civil infrastructures such as bridges and buildings would be included. Harne imagines tiny trees feeding voltages to a sensor on a girder deep inside a high-rise apartment or on the underside of a bridge in the near future. He said the project takes benefits from lots of vibrational energies that surround us all day. Some of them are wind-induced structural motions, human activity, and even seismic activity.
“Buildings sway ever so slightly in the wind, bridges oscillate when we drive on them and car suspensions absorb bumps in the road,” he said. “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.”
He explained that the soundness of a structure is monitored by detecting the vibrations that pass through it and the primary target of the project is to convert those vibrations into electricity in order to power the structural monitoring system by the same vibrations being monitored. If the sensors could capture vibrational energy their data could be wirelessly transmitted in a true self-sufficient way and the maintenance cost of batteries could be reduced.
Harne and his colleagues experimented a mathematical model, where they built a small tree like device out of steel beams ( one is a tree trunk and another is a branch), connected by a strip of electromechanical material, polyvinylidene fluoride (PVDF), to convert the structural swing into electrical energy.
After installing the model tree on a device that shook it back and forth at high frequencies, it didn’t seem to move at first as the device oscillated with only small amplitudes at a high frequency. Finally, the tree produced a small voltage from the motion: about 0.8 volts.
By adding noise to the system, they created a situation called “saturation phenomena,” that sent the tree to a tipping point where the high-frequency energy was suddenly channeled into a low-frequency oscillation that produced more than double the voltage, around 2 volts.
Albeit the voltages were low, but the experiment was a proof of concept that random energies are able to generate vibrations that are useful to generate electricity.