Today, underwater sensors cannot share data with those on land, as both use different wireless signals that only work in their respective mediums. Radio signals that travel through air die very rapidly in water.
Acoustic signals, or sonar, sent by underwater devices mostly reflect off the surface without ever breaking through. This causes inefficiencies and other issues for a variety of applications, such as ocean exploration and submarine-to-plane communication.
MIT Media Lab researchers have designed a system that tackles this problem in a novel way. An underwater transmitter directs a sonar signal to the water’s surface, causing tiny vibrations that correspond to the 1s and 0s transmitted. Above the surface, a highly sensitive receiver reads these minute disturbances and decodes the sonar signal.
Using the “Translational Acoustic-RF communication” (TARF) system, military submarines, for instance, wouldn’t need to surface to communicate with airplanes, compromising their location. And underwater drones that monitor marine life wouldn’t need to constantly resurface from deep dives to send data to researchers. Another promising application is aiding searches for planes that go missing underwater.
TARF includes an underwater acoustic transmitter that sends sonar signals using a standard acoustic speaker. The signals travel as pressure waves of different frequencies corresponding to different data bits.
To achieve high data rates, the system transmits multiple frequencies at the same time, building on a modulation scheme used in wireless communication, called orthogonal frequency-division multiplexing. This lets the researchers transmit hundreds of bits at once.
The radar, which looks like a pair of cones, transmits a radio signal that reflects off the vibrating surface and rebounds back to the radar. Due to the way the signal collides with the surface vibrations, the signal returns with a slightly modulated angle that corresponds exactly to the data bit sent by the sonar signal.
TARF is the first system that demonstrates that it is feasible to receive underwater acoustic transmissions from the air using radar. this new radar-acoustic technology will benefit researchers in fields that depend on underwater acoustics (for example, marine biology), and will inspire the scientific community to investigate how to make radar-acoustic links practical and robust.
The researchers also hope that their system could eventually enable an airborne drone or plane flying across a water’s surface to constantly pick up and decode the sonar signals as it zooms by.
News Source: http://news.mit.edu/2018/wireless-communication-through-water-air-0822
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