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Soon, vibrating windows to stop outside sound waves in their tracks

A team of researchers at the Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Germany, have developed a vibrating window that negates noise generated by sources as loud and shrieking as jet planes.

Washington, May 1 : A team of researchers at the Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Germany, have developed a vibrating window that negates noise generated by sources as loud and shrieking as jet planes.

"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 the institute.

Traditionally, to obstruct intrusion of noise through windows, engineers thicken the glass to double or even triple panes. But there is disadvantage to it; the process drives up the cost of construction.

Now, Bein and his team have developed a method that thwarts vibration with vibration, effectively negating the interference of outside noise through glass windows. The trick, they say, is to stop the sound waves in their tracks.

The process uses postage stamp-sized patches made of a ceramic called piezoelectric material, to behave 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, the team was able to reduce noise of 90-100 decibels (the sound of a subway or power mower) by 50 percent.

According to the scientists, the invention could find its way for use in apartments, hotels and offices within five years.

But, still there is the cost factor.

According to Gary Koopmann, professor of mechanical engineering and director of the Center for Acoustics and Vibration at Pennsylvania State University in University Park," the main hurdle to transition to a practical application is the cost".

"Every window needs to be wired and maintained, which adds to the bottom line. In addition, different kinds of sound, particularly those that are steady, are easier for the computer controller to respond to rapidly and generate an appropriate noise-cancelling vibration. Sounds that disappear or change quickly are more difficult to manage," said Prof. Koopmann.

"For airport noise, the noise is transient. To have a control system respond instantly to a transient sound coming in is nearly impossible," Discovery News quoted him as saying.

Bein and his team are now working to make the system reliable and bring the cost down.

ANI