Divers could soon communicate underwater over large distances by sending radio messages along the water鈥檚 surface, getting around the fact that radio frequencies can鈥檛 travel far through water.
Alternative communication systems that use sound, such as sonar, can transmit across long distances underwater, but these methods can鈥檛 carry large amounts of information, are relatively slow to reach their recipient and can disturb marine wildlife.
Now, , a co-founder of communication technology firm Saltenna in California, and his colleagues have found a way to communicate using radio waves by exploiting the way electromagnetic radiation travels along the water鈥檚 surface. 鈥淭wo divers, for instance, completely submerged in the water, all of a sudden can use their walkie-talkies,鈥� says Smolyaninov.
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This makes sense according to an idea called the principle of least time, proposed by Pierre de Fermat in the 17th century, he says. This predicts that light, a form of electromagnetic radiation, will always take the quickest possible path to its destination.
Smolyaninov and his colleagues have shown mathematically that light should naturally travel along the surface of water at radio frequencies, in a special kind of wave propagation. They then designed an antenna that can direct and receive radio waves that have passed vertically through a small amount of water to make use of this surface wave.
鈥淪ince you鈥檙e doing it in the radio frequency range, at high frequencies, you can sample lots of information over this channel,鈥� says Smolyaninov, such as live high-definition video from underwater.
In tests in a freshwater lake, the researchers found that divers using these antennas could communicate via radio over distances many times further than would be possible if they were sending the signal directly through the water. The maximum distance is greater the closer to the surface you are. At 8 metres below the surface, it works out to be around 10 metres.
The technology might have applications for connecting divers separated by large distances, hundreds of metres or more, but it is still limited to being used relatively close to the water鈥檚 surface, says at Imperial College London. This is because the signal will need to travel through water to reach the surface. 鈥淭hey can鈥檛 go any deeper than anybody else, but what they can do is to go far across the surface,鈥� he says.
Scientific Reports
