Ear-Piercing Sounds Harvested for Energy

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Engineers have figured how to harvest energy from sound; a neat physics trick that could soon lead to quieter jet engines, heavy construction equipment and factory machines, and perhaps a new way to generate wind power.

Separate teams of investigators have developed prototype devices that create small amounts of energy, just enough to run sensors inside noisy places. These sensors can then be used to actually dampen the sound of the noise itself, according to Stephen Horowitz, a research engineer at Ducommun Miltec, an aerospace contractor based in Huntsville, Ala.

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Horowitz said he began looking at the problem a decade ago while a student at the University of Florida. “We were looking at engine liners and noise reduction technologies to quiet engines,” Horowitz said. “We began looking at the fact that there is a lot of acoustic energy in that environment.”

Over time, Horowitz and his colleagues realized the incredible roar of the jet engine, which revs at more than 130 decibels (enough to induce pain) could be changed into electrical energy. Horowitz and his graduate advisor professor Mark Sheplak did this with something called piezoelectrics. Piezoelectric material takes the stress and strain of mechanical motions -- like bending of wires or pushing down on a pad, for example -- and turns it into an electrical charge.

Using piezoelectric material, they built an extremely sensitive and thin membrane out of aluminum that could turn the vibrations caused by sound into electricity, just enough to power a small sensor. Horowitz said the advantage of a sound-powered sensor is that you don’t have to use batteries or wires to run the engine sensor, making it easier to maintain.

The next phase was to attach the membrane to a special liner that dampens engine noise by canceling certain frequencies. The project to build such an noise-cancelling device is being funded by NASA, which is helping commercial aircraft makers come up with quieter jet engines.

A similar effort is underway at Georgia Tech, where professor of mechanical engineering Ken Cunefare and colleagues have built a device to harvest the noise of hydraulic pumps and valves used in a variety of industrial machines. These hydraulic pumps make sound by the movement of fluid in enclosed space. Cunefare’s device also runs sensors that can give valuable information about how the machines are performing, and perhaps one day how to make them quieter.

“Hydraulics drive every kind of construction equipment on the planet,” Cunefare said. “If you could improve the energy conversion by couple of orders of magnitude, you could reduce overall noise as well. It’s sort of the Holy Grail.”

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Cunefare said there’s not a whole lot of energy out there waiting to be captured, but even a tiny amount can make a big difference in a complex machine. He says two firms are interested in the device and he expects it to be commercialized in the next three to five years.

In 2011, a Dutch engineering group figured out an application of harvesting energy from the sound of wind as it blows across a small opening (like the sound make by blowing over the top of a beer bottle).

While it does sound a little far-fetched, such a device -- if replicated on a larger scale -- would have fewer moving parts than existing wind turbines, Horowitz noted.

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