April 30, 2007 — The roar of jets. The shriek of car alarms. The din of traffic. All-intrusive noises can distract us from our work and keep us awake at night.
But help is on the way for the restless and sleepless. A noise-negating method that thwarts vibration with vibration could be available for use in apartments, hotels and offices in five years.
"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, head of the business unit for energy, environment and health at Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Germany.
To make windows work less like loudspeakers, engineers thicken the glass to double or even triple panes. But that can drive up the cost of construction. Ideally they'd like to stop the sound waves in their tracks.
Bein and his team developed a method to do just that. They used postage stamp-sized patches made of a ceramic called piezoelectric material, which behaves both like a sensor and vibration generator when shot with an electric charge. (The material can be made transparent and imbedded in the glass, too, although the team has not yet accomplished this step with the window.)
Wires running through the window link the stamp-sized patches to a computer controller and an amplifier. When a sound-generated vibration rattles the window, the piezoelectric patch senses it.
That data goes to the controller, which in turn delivers a specific electric charge back up to the patch, causing it to vibrate at a phase that ideally cancels out the sound vibrations.
In laboratory experiments, they were able to reduce noise of 90-100 decibels (the sound of a subway or power mower) by 50 percent.
