Acoustic Time Reversal Underwater Broadband
Acoustic time reversal can lead to transfer rates of up to 15 kilobits per second at a range of four kilometers. This is far better than existing techniques and, over long distances, even compares to what whales can do.
William Kuperman and colleagues at the Scripps Institution of Oceanography in La Jolla, California, US, and researchers from the NATO Undersea Research Centre in La Spezia, Italy, have been testing the technique in the Mediterranean.
Time reversal exploits the way undersea acoustic signals typically arrive clouded by echoes that travel at different speeds. For example, a "ping" may arrive as three separate sounds – one that travelled directly, an echo from the surface and then an echo from the ocean floor.
If the receiver transmits the same sequence of sounds backwards, they will take the same routes back to the original source. But because the sound that took the longest to travel is sent first, the second-slowest next, and the fastest last, all three will arrive at about the same time at the original source.
In effect, they converge in time, reconstructing the original signal. The retransmitted sounds will create echoes of their own, but the original signal is strong enough to stand out, say the researchers.
A similar system is used in SeaQuest DSV, a television show that ran from 1993-96.
Via 'Time reversal' allows wireless broadband under the sea; thanks to Moira for writing in with the tip.
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