Free Speech, Free Energy: Researchers turn ambient sound into power

By Michael Clark

Cell phones have become a ubiquitous piece of technology. Never before has a technology become so common,so fast. Not that it didn’t deserve it. The cell phone packs an amazing number of conveniences into a single device. That glossy black lump of plastic is at once a computer, a camera, a planner, a recorder, and, of course, a telephone that needs neither wire nor quarter to communicate. The centrality of cell phones to our lives makes it seem nothing short of a tragedy when the batteries go dead, effectively ending our relationship with the world outside of shouting distance.

This simple truth has given rise to a host of solutions. Solar chargers, supplemental batteries, and even hand cranked-chargers litter the market with promises of restoring your telecom lifeline. However, none has quite the audacity of Dr. Sang-Woo Kim’s recharging device: it restores battery life with sound.

Dr. Kim’s Institute of Nanotechnology at Sungkyunkwan University in Seoul, South Korea is working on ways to scavenge energy from the environment, namely sound energy. Sound produces vibrations, and Dr. Kim’s technology converts those vibrations into an electrical charge. Sound is picked up by a sound-absorbing pad, which causes zinc oxide wires to vibrate between two electrodes. The wires compress and release, which generates a small current. Sound is picked up from conversations, as well as environmental noise like traffic or music.

The technology has to improve significantly if it is to be ready for everyday use. Initial experiments show that 100 decibels of sound can be converted into only 50 millivolts. Dr. Kim says that’s enough to fuel some low-power sensors and implantable devices, but it isn’t quite enough energy to properly charge a cell phone battery yet. He hopes that by experimenting with different materials he will be able to find ways to generate more power with lower sound levels.

One day, the sound-converting technology could be used in a variety of low-power consumption electronics. But Dr. Kim also suggests that sound-insulating walls could be placed near highways. This is especially good news for people living in urban areas or near busy streets where ambient noise comes in a constant stream. Not only would this technology generate some electricity from the sound of passing vehicles, but it would reduce the amount of noise pollution in the surrounding area by absorbing the vibrations.

Using sound energy is just one of the ways scientists are scavenging energy from the environment. As nano-generator technology improves, portable electronic devices may be able to be charged by a simple pinch of the fingers, everyday movement like walking or running, or even a human heartbeat. Already, watches exist which translate body motion into enough energy to recharge a watch. With the world’s demand for energy only going up, recovering waste energy will become ever more important.

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