By Lola Gayle, Editor-at-large
Renewable energy comes in a variety of sources, such as sun, wind, rain, tides, waves, and geothermal heat.
One of the most popular forms of renewable energy comes from wind power, which is generated by massive wind turbines or sails clustered together in wind farms.
If you’ve ever driven across the state of Texas, you may have seen some of these wind farms. They’re impressively huge and can be seen from quite a long distance away.
While wind power is a great alternative to burning fossil fuels, those giant turbines certainly don’t go with the landscape, and they can be costly to manufacture and transport. I’ve seen a few of these turbine blades making their way down the highway or railroad tracks, often taking 2 flatbed 18-wheelers or train cars to carry one single blade.
Now, Ohio State University researchers are proposing new tools for harvesting wind energy that look less like giant windmills and more like tiny leafless trees, and it all revolves around turning “good vibrations” into energy.
In 2016, the research project set about testing whether high-tech objects that look a bit like artificial trees can generate renewable power when they are shaken by the wind — or by the sway of a tall building, traffic on a bridge or even seismic activity.
Shaken, not stirred
In a Journal of Sound and Vibration article, the researchers report how they uncovered something new about the vibrations that pass through tree-shaped objects when they are shaken. During their research, the team found that tree-like structures made with electromechanical materials are capable of converting random forces like wind or footfalls on a bridge into strong structural vibrations that are ideal for generating electricity.
Before you start imagining fields of huge mechanical trees swaying in the breeze, the researchers say the technology could prove most valuable when applied on a small scale in situations where other renewable energy sources such as solar are not an option, said project leader Ryan Harne, assistant professor of mechanical and aerospace engineering at Ohio State, and director of the Laboratory of Sound and Vibration Research.
The “trees” themselves would be very simple structures: think of a trunk with a few branches — no leaves required.
Tiny kinetic trees
One example of where this technology could be used is to power sensors that could monitor the structural integrity and health of buildings and bridges. Harne envisions tiny trees feeding voltages to a sensor on the underside of a bridge, or on a girder deep inside a high-rise building.
The project takes advantage of the plentiful vibrational (kinetic) energy that surrounds us every day, he said. Some sources are wind-induced structural motions, seismic activity and human 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.”
Sensors monitor the soundness of a structure by detecting the vibrations that pass through it, he explained. The initial aim of the project is to turn those vibrations into electricity, so that structural monitoring systems could actually be powered by the same vibrations they are monitoring.
The current method of powering structural sensors uses batteries or traditional power lines. Instead, if those sensors could get their energy from vibrations, they could acquire and wirelessly transmit their data is a truly self-sufficient way.
To test their theories, Harne and his team used mathematical modeling to determine that it is possible for tree-like structures to maintain vibrations at a consistent frequency so that the energy can be effectively captured and stored via power circuitry, a phenomenon known as internal resonance.
By exploiting this internal resonance, Harne found that he could coax an electromechanical tree to vibrate with large amplitudes at a consistent low frequency, even when the tree was experiencing only high frequency forces. It even worked when these forces were significantly overwhelmed by extra random noise, as natural ambient vibrations would be in many environments.
The team then tested out the model by building a tree-like device out of two small steel beams — one acting as the “trunk” and the other as the “branch.” They were connected by a strip of an electromechanical material to convert the structural oscillations into electrical energy.
Once the model tree was installed, it shook back and forth at high frequencies, even though it didn’t seem to be moving at all. However, the electromechanical material, polyvinylidene fluoride (PVDF), did indeed produce about 0.8 volts from the motion.
The next step was to add 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,” reaching a tipping point where the high frequency energy was suddenly channeled into a low frequency oscillation causing the tree to sway 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.
Despite the low voltages produced, this proof-of-concept project was enough to prove that random energies can produce vibrations that are useful for generating electricity.
“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,” Harne concluded.
Further studies will be needed, but it seems like a step in the right direction. And perhaps someday, our wind farms might look more like a sculpture garden. A girl can dream can’t she?