FROM Bluetooth and Wi-Fi to FM and AM, wireless communication depends on electromagnetic waves—usually, radio waves. But as any motorist driving through a tunnel or under power lines can attest, such waves cannot always propagate properly past every obstruction. Sometimes, a system that used a different medium of transmission would make communication that bit easier.
As they report in the Proceedings of the National Academy of Sciences, Alex Zettl and his colleagues at the University of California, Berkeley, think they have devised such a system. Instead of radio waves they use ultrasound. By exploiting sound at frequencies above the 20 kHz limit of human hearing they can, in principle, send messages that neither affect nor are affected by human conversation and other everyday noises that take place at lower pitches.
Ultrasonic transmitters and receivers have been around for a long time. But they usually employ the piezoelectric effect, whereby an alternating electric current causes them to vibrate if transmitters or, if receivers, to generate an electric current in response to vibration. This means their range is restricted by their resonant frequencies—which in turn restricts their bandwidth, and thus the amount of information they can handle.
More conventional diaphragm-based equipment has a wider frequency range than...
from The Economist: Science and technology http://ift.tt/1Hl5302
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