Noise-Cancelling Windows With Piezoelectric Patches
There's nothing like a nice, thick wall to shield you from noisy urban environments. Windows pose a real problem because of the way they transmit vibration.
"A window acts like a loudspeaker and a membrane. If you control the vibration of the window, you can control transmitted noise in such a way that it is not acting like a membrane or a loudspeaker," said Thilo Bein, Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Germany.
Simple expedients like using triple-pane windows can help, but they are expensive; it would be better to eliminate the vibration. Bein and his research team have developed a way to make a single-pane window damp out vibration by about fifty percent.
Here's how it works. Stamp-sized patches of a piezoelectric ceramic are attached to the window at regular intervals; they are connected to each other and to a controller by fine wires. When a sound-generated vibration moves the window, the patches sense it.
The controller then delivers a specific electric charge back to the patches, causing them to vibrate at a phase that cancels out the sound vibration. In experiments, 90-100 decibel noise was reduced by fifty percent. Bein estimates that these windows would be commercially available within five years; the patches would be more fully integrated into the window (and hopefully transparent).
Science fiction writers of the 1950's were very concerned with noise reduction, apparently. For instance, in his 1957 story Silence Please, Arthur C. Clarke wrote about the Fenton Silencer:
It consisted of a microphone, a special amplifier and a pair of loud speakers. Any sound that happened to be about was picked up by the mike, amplified and inverted so it was exactly out of phase with the original noise. Then it was pumped out of the speakers, the original wave and the new one cancelled out, and the net result was silence...
(Read more about Clarke's Fenton Silencer)
SF fans will doubtless remember the hush corner from Heinlein's Double Star as well as the legendary cone of silence from Dune.
Scroll down for more stories in the same category. (Story submitted 5/1/2007)
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