Of the many ways energy is conveyed on our planet, one that seemingly goes unnoticed is what appears to be otherwise random vibrations, such as oscillations set up in a structure by wind passing over it, seismic energy traveling through the ground, or regular traffic sending vibrations through a bridge. Typically these energies pass through the structure in question, sometimes causing problems, and sometimes going completely unnoticed — but can these energies be put to use? A proposal to harness these seemingly random vibrations has been made by a research team from Ohio State University, using simple structures that resemble trees. “Buildings sway ever so slightly in the wind, bridges oscillate when we drive on them and car suspensions absorb bumps in the road,” explains Ohio State assistant professor Ryan Harne, director of the Laboratory of Sound and Vibration Research. “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.” In the past, it was assumed that the vibrations that could be absorbed by such a collection device were too random to be a reliable source of energy. Harne’s team, however, found that an artificial tree-like structure could maintain these vibrations at a constant frequency, despite it’s seemingly random source, via a phenomenon he calls "internal resonance": high-frequency vibrations experienced by the structure can be converted to lower-frequency waves, and converted to electrical energy. The team built a simple "tree", consisting of two steel beams, a trunk and one branch, each connected by an electro-mechanical material to convert motion into electricity. They found that by subjecting it to high-frequency vibrations, the apparatus provided 0.8 volts, despite not appearing to have any motion at all. After adjusting the vibrations to appear as if they were coming more from one direction than another, the tree more than doubled it’s output, up to 2 volts. While this doesn’t sound like a great deal of electrical energy, the experiment is a proof-of-concept model, and could conceivably generate much more practical amounts of energy if used in larger numbers.
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