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In science’s quest to develop less polluting sources of energy, hydrogen gas has often been used as an example as a potential replacement for fossil fuels: aside from being the most abundant substance in the universe, it is also the most combustible natural substance known, and only produces pure water when burned with oxygen. Unfortunately, the chemical instability of its gaseous form means that storing it is inherently hazardous, and the extraction of the gas from hydrogen’s more stable forms, such as water or petroleum products, can be highly energy inefficient, or produce a disproportionate amount of waste pollutants.
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As our culture makes the shift away from carbon-intensive energy sources, alternative sources like solar energy from photovoltaic cells are becoming an attractive option. However, while the cost of producing solar cells has been decreasing steadily in recent years, they still require a great deal of resources to make: the silicon crystals that solar cells use not only require hazardous solvents for their production, they also need to be baked at high temperatures — 1,000ºC (1,832ºF) — to attain the purity required for their use, an energy-intensive process that can increase the final product’s carbon footprint.
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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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