MIT’s underwater sensor offers low-power long-range signals

The team plans to build battery-free underwater networks.
Sejal Sharma
The device enables battery-free underwater communication
The device enables battery-free underwater communication


Deep Sea exploration is about to get more accessible. Researchers at the Massachusetts Institute of Technology (MIT) have developed and demonstrated a technology that can transmit underwater signals spanning kilometers with a relatively low reader transmit power.

The researchers are calling their tech Van Atta Acoustic Backscatter (VAB), which can be used to map the pulse of the ocean. A submerged network of underwater sensors can continuously measure ocean vital signs like the temperature, pressure, and dissolved carbon dioxide to create more accurate climate change models and monitor the efficacy of carbon capture technologies, explained the researchers in their study.

What are underwater backscatters?

The technology is based on underwater backscatters. Backscatter is the reflection of a signal, in this case, sound waves, back in the direction from where it originated. Backscatter has many applications. It is used in medical ultrasounds to understand what’s happening inside the human body. Still, in marine sciences, backscatter from sound waves helps us understand the characteristics of the sea floor.

Now, other underwater communication strategies exist, but they require a lot of energy resources. What sets underwater backscatters apart is that they communicate by reflecting rather than generating acoustic signals, which makes them very energy efficient.

Energy-efficient and long-range network

The researchers tested the ability of their device in a river and an ocean and found that the communication range was more than 15 times farther than previous devices. “Its key innovation lies in how it modulates these reflections through a retroreflective structure - which allows it to boost the communication range of underwater backscatter by up to an order of magnitude over state-of-the-art designs,” explained the study.

“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. There are still a few interesting technical challenges to address, but there is a clear path from where we are now to deployment,” said 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, as per MIT’s press release.

A key factor that obstructs the range of underwater backscatter communication is that the signals traveling from the nodes to the hydrophone (receiver) get spread out in all directions. Nodes are used in underwater backscatter communication devices to receive and reflect sound waves.

This spreading out of signals weakens the communication and the amount of power that arrives back to the hydrophone ends up being a very small fraction of the one that originally arrived at the backscatter node.

To overcome this challenge, the researchers explained in the press release that they leveraged a 70-year-old radio device called a Van Atta array, in which symmetric pairs of antennas are connected so that the array reflects energy in the direction it came from.

Funding of $200 million for underwater sensing tech

“We are creating a new ocean technology and propelling it into the realm of the things we have been doing for 6G cellular networks. For us, it is very rewarding because we are starting to see this now very close to reality,” Adib says.

Organizations like DARPA, the National Science Foundation, and venture capital firms have funded underwater sensing technologies by $200 million in the last year alone.

The researchers plan to continue their research around the Van Atta Acoustic Backscatter, and use boats this time to evaluate communication ranges of their device. They will also release their findings via research papers and tools so other researchers can build on their studies. The long-term plan is to commercialize this technology so it can be utilized to monitor climate and coastal change.

Study abstract:

We present the design, implementation, and evaluation of Van Atta Acoustic Backscatter (VAB), a technology that enables long-range, ultra-low-power networking in underwater environments. At the core of VAB is a novel, scalable underwater backscatter architecture that bridges recent advances in RF backscatter (Van Atta architec- tures) with ultra-low-power underwater acoustic networks. Our design introduces multiple innovations across the networking stack, which enable it to overcome unique challenges that arise from the electro-mechanical properties of underwater backscatter and the challenging nature of low-power underwater acoustic channels. We implemented our design in an end-to-end system, and evaluated it in over 1,500 real-world experimental trials in a river and the ocean. Our evaluation in stationary setups demonstrates that VAB achieves a communication range that exceeds 300m in round trip backscat- ter across orientations (at BER of 10−3). We compared our design head-to-head with past state-of-the-art systems, demonstrating a 15× improvement in communication range at the same throughput and power. By realizing hundreds of meters of range in underwater backscatter, this paper presents the first practical system capable of coastal monitoring applications. Finally, our evaluation represents the first experimental validation of underwater backscatter in the ocean.

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