The idea is every sound wave "contains all the information to locate where its source was," said physicist Mathias Fink at Universit� Paris 7.

In experiments, the researchers found touching an object, such as a window or a table, generates vibrations that are easily detectable with one or two acoustic sensors placed on the item in question.

"When you give a table a touch, there will be a lot of reverberations -- a very long signal to record," Fink said at the annual meeting of the Acoustical Society of America.

Computer software then can reverse the sound wave and pinpoint exactly where the source lies in the room. This concept, known as time reversal, is how ultrasound surgery that breaks up kidney stones can focus pulses on targets, explained researcher Stefan Catheline, also at Universit� Paris 7.

The new technology quickly deduces the source of the vibration made by a touch. Specific locations therefore can become virtual switches for remote control. A person could turn on a light, switch on a computer or turn up the volume on a stereo just by the touch of a finger to a table or door.

Technically, this should only require an acoustic sensor or two and a very small amount of computer power, the researchers said. The maximum distance a basic sensor can detect a touch on a surface on which it lies is about 20 feet, Fink said.

One of the scientists has created the Parisian company Sensitive Object to commercialize the notion.

"The great advantage that appeared right away was that this technique was very cheap -- a personal computer and a standard $3 accelerometer was used," Catheline said.

In addition, the system was simple, performing acoustic signal analysis in real time. Moreover, the setup is "universal -- the only restriction is that sound must propagate through the object, which is the case for almost all everyday life objects," Catheline explained.

Every surface can become a touch screen, Fink said. The markets for the device could include store enhancements, home automation, games, artist performances "and probably a lot we are not even thinking about right now," he added.

For instance, Fink said the lamp shop Illumina in Paris made its storefront interactive, so passersby now can activate lamps inside by touching virtual buttons on the window. A representative from Sensitive Object suggested other shops could have potential customers activate electrical trains or puppets in just the same way.

"The biggest market the company is working in right now are companies that build switches, to replace mechanical switches," Fink said, adding that the first product should come out next year.

A computer can be trained to distinguish how touches on different points on a surface as close as an inch together sound like. This allows an object to have multiple buttons. Thus, schools can turn blackboards or desks into computer keyboards so students can see their results on classroom screens, Fink said. Old computer monitors can be rendered into touch screens as well, he added.

The researchers also are working on a system that can follow people as they walk around a room, Fink said. This way, museums can control the lighting around a statue or other artwork depending on where a viewer stands in relation to it, the company noted.

"It's great work. It looks like an inexpensive way to manufacture devices that are interactive," said geophysicist Don Albert of the U.S. Army's Cold Regions Research and Engineering Laboratory in Hanover, N.H.

"The sensor cost is very low," he told UPI. "I can see it embedded in glass when manufactured."

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