Have you ever asked yourself what is ultrasound in electronic world?
Now is time to reveal that information.
A beam of sound can now be projected across a room like a spotlight picking out a single person in a crowd for a private message.
The uncanny effect developed by an engineer at the Massachusetts Institute of Technology, could have many applications, from public address systems to hi-fi.
A football manager could direct advice to any player on the field, unheard by all the others, or an airport could use it to deliver announcements only to those who need to hear them. More eerily, the technology makes it possible to whisper into a person`s ear at a range of 50 metres.
The Audio Spotlight has been developed by Joe Pompei, 26, who is studying for a PhD at the Media Lab at MIT. Among its first users will be British Airways, one of the sponsors of the Media Lab, who yesterday asked Mr Pompei to demonstrate it at their headquarters at Heathrow. It has cost less than £62,000 to develop.
A loudspeaker, says Mr Pompei, broadcasts sound in every direction just as a lightbulb spreads light. "As a laser is to a lightbulb, so this invention is to a loudspeaker," he said. "it puts sound just where you want it and nowhere else." The narrow beam of sound is produced by transducers working in the same way as the diaphragm of a loudspeaker. But the transducers operate at much higher frequencies producing ultrasound beyond the range of the human ear.
The dispersion of a sound beam depends on the ratio between the frequency of the sound and the size of the source. Because the frequency is so high, a narrow beam diverging at an angle of only three degrees is produced by Mr Pornpei`s transducers. As the inaudible ultrasound waves move through the air they begin to distort because of the imperfect elasticity of the air. The process of distortion produces waves that do fall into the audible range.
The distortion is predictable, not random, which means that by manipulating the original ultrasound signal, it can be made to degrade not into noise but into recognisable sound. Mr Pompei has written a
computer programme that can turn an original source of sound into an ultrasound beam that degrades to reproduce the original sound - but only within the narrow ultrasound beam - so only those in the line of the beam will hear the sound that is produced.
times aug 5th 99