Underwater backscatter communication devices use an array of nodes made from “piezoelectric” materials to receive and reflect sound waves. These materials produce an electric signal when mechanical force is applied to them.
They tested the array in more than 1,500 experimental trials in the Charles River in Cambridge, Massachusetts, and in the Atlantic Ocean, off the coast of Falmouth, Massachusetts, in collaboration with the Woods Hole Oceanographic Institution. The device achieved communication ranges of 300 meters, more than 15 times longer than they previously demonstrated.
The researchers plan to continue studying underwater backscatter Van Atta arrays, perhaps using boats so they could evaluate longer communication ranges. Along the way, they intend to release tools and datasets so other researchers can build on their work. At the same time, they are beginning to move toward commercializing this technology.
“Limited range has been an open problem in underwater backscatter networks, preventing them from being used in real-world applications,” says Omid Abari, assistant professor of computer science at the University of California-Los Angeles, who wasn’t involved with this work. “This paper takes a significant step forward in the future of underwater communication by enabling them to operate on minimum energy while achieving long range. The paper is the first to bring Van Atta reflector array technique into underwater backscatter settings and demonstrate its benefits in improving the communication range by orders of magnitude. This can take battery-free underwater communication one step closer to reality, enabling applications such as underwater climate change monitoring and coastal monitoring.”
Building off their group’s work on RFIDs, the team carefully crafted a model that captured the impact of system parameters, like the size of the piezoelectric nodes and the input power of the signal, on the underwater operation range of the device.
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Using this model, they showed that an underwater backscatter array can potentially achieve kilometer-long communication ranges.
This device is an array of piezoelectric transducers that enables battery-free underwater communication. Image courtesy of the researchers.
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“What started as a very exciting intellectual idea a few years ago—underwater communication with a million times lower power—is now practical and realistic,” says Fadel Adib, associate professor in the Department of Electrical Engineering and Computer Science and director of the Signal Kinetics group in the MIT Media Lab. “There are still a few interesting technical challenges to address, but there is a clear path from where we are now to deployment.”
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In addition, they used a technique called cross-polarity switching to encode binary data in the reflected signal. Each node has a positive and a negative terminal (like a car battery), so when the positive terminals of two nodes are connected, and the negative terminals of two nodes are connected, that reflected signal is a “bit one.”
This research was funded, in part, by the Office of Naval Research, the Sloan Research Fellowship, the National Science Foundation, the MIT Media Lab, and the Doherty Chair in Ocean Utilization.
For instance, the researchers needed to derive a function that captures the amount of signal reflected out of an underwater piezoelectric node with a specific size, which was among the biggest challenges of developing the model, Akbar adds.
When building the Van Atta array, the researchers found that if the connected nodes were too close, they would block each other’s signals. They devised a new design with staggered nodes that enables signals to reach the array from any direction. With this scalable design, the more nodes an array has, the greater its communication range.
Device Offers Long-Distance, Low-Power Underwater Communication
System could be used to aid monitoring climate and coastal change
They evaluated the model on data from their experimental trials and found that it could accurately predict the range of retrodirected acoustic signals with an average error of less than one decibel.
Published: Monday, September 25, 2023 – 12:01