A packet filled with polyvinylidene fluoride converts vibrations into electricity-
'He and his colleagues tested the mathematical model in an experiment, where they built a tree-like device out of two small steel beams—one a tree “trunk” and the other a “branch”—connected by a strip of an electromechanical material, polyvinylidene fluoride (PVDF), to convert the structural oscillations into electrical energy.
They installed the model tree on a device that shook it back and forth at high frequencies. At first, to the eye, the tree didn’t seem to move because the device oscillated with only small amplitudes at a high frequency. Regardless, 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.
Those are low voltages, but the experiment was a proof-of-concept: Random energies can produce vibrations that are useful for generating electricity.'
Energy can be harvested from random vibrations of objects, study says
Random vibrations of objects like mechanical trees can be used to harvest energy including electrical energy, a new project by researchers at Ohio State University has shown.
According to the study published in the Journal of Sound and Vibration, random doesn’t always have to be random and when it comes to harnessing energy, even the seemingly random swaying of trees can be used to generate power.
Researchers at the University have demonstrated special electromechanical structures that can convert the random forces caused by winds, footfalls on bridge into strong structural vibrations that can eventually be harnessed to generate electricity. They have come up with the idea after they uncovered something new about the vibrations that pass through tree-shaped objects.
While these tree-shaped objects do not necessarily mean a whole land filled with mechanical trees, project leader Ryan Harne, assistant professor of mechanical and aerospace engineering at Ohio State, and director of the Laboratory of Sound and Vibration Research explains that’s not the case. The reason they are dubbing these structures as tree-like is that they are simple structures – think of a trunk with a few branches— without any leaves.
Researchers say that some of the early applications of their technology would include powering the sensors that monitor the structural integrity and health of civil infrastructure, such as buildings and bridges. The way it would work is that these tiny trees would feed voltages to a sensor on the underside of a bridge, or on a girder deep inside a high-rise building taking advantage of the plentiful vibrational energy that surrounds us every day. 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,” Harne 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.
Today, the only way to power most structural sensors is to use batteries or plug the sensors directly into power lines, both of which are expensive and hard to manage for sensors planted in remote locations. If sensors could capture vibrational energy, they could acquire and wirelessly transmit their data is a truly self-sufficient way.
While there have been studies that have looked into using tree-like devices to capture wind or vibration energies, their work was based on testing the effectiveness of such a system using ideal situation that the vibrations are not random. Further, there haven’t been concrete efforts in the direction of capturing energy from realistic ambient vibrations with a tree-shaped electromechanical device—mainly because it was assumed that random forces of nature wouldn’t be very suitable for generating the consistent oscillations that yield useful electrical energies.
In the latest study, Harne determined that it is possible for tree-like structures to maintain vibrations at a consistent frequency despite large, random inputs, so that the energy can be effectively captured and stored via power circuitry. The phenomenon is called internal resonance, and it’s how certain mechanical systems dissipate internal energies. Harne determined that he could exploit internal resonance to 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.
He and his colleagues tested the mathematical model in an experiment, where they built a tree-like device out of two small steel beams—one a tree “trunk” and the other a “branch”—connected by a strip of an electromechanical material, polyvinylidene fluoride (PVDF), to convert the structural oscillations into electrical energy.
They installed the model tree on a device that shook it back and forth at high frequencies. At first, to the eye, the tree didn’t seem to move because the device oscillated with only small amplitudes at a high frequency. Regardless, 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.
Those are low voltages, but the experiment was a proof-of-concept: 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 said.
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