Acoustic Modems Reach Underwater Where Radio Signals Can't

Communicating by sound underwater works great for dolphins and whales, so an NJIT expert decided to try a new variant of this method for autonomous vehicles, divers and sensors, too.

Radio signals used by traditional wireless devices become too weak underwater, explained Ali Abdi, a professor of electrical engineering and director of the Advanced Communication and Signal Processing Laboratory, in NJIT’s Center for Wireless Information Processing.

But sound has long been used to send data — the noise a fax machine makes when it’s connecting is evidence of one easy-to-understand example — and the fundamental idea dates back much longer. Abdi referred to an insight attributed to Leonardo da Vinci in the last 15th century: "If you cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you."

"There's always a question of how we can make things better, how we can make them faster,” Abdi noted. “We showed that acoustic particle velocity channels can be used in parallel with the conventional acoustic pressure channel to transmit multiple data streams. … We have been able to modulate data on the vibrations of water particles."

Abdi first developed and tested his idea with mathematical analysis and computer simulations. Now, using a testbed, he can send data at sea. Real-world examples, he observed, include remote monitoring of underwater construction and tools; environmental factors in offshore oil rigs; continuous observation of ocean phenomena to predict and prepare for natural disasters; fishing industry communications; military applications and many others.

Abdi’s work is funded by the National Science Foundation, which awarded him an additional $49,000 in July, bringing his total to almost $300,000 since 2015. He is assisted by postdoctoral researcher Erjian Zhang.

Abdi’s co-principal investigator is Michael Ehrlich, associate professor of finance in the Martin Tuchman School of Management, who served as an industry mentor for the grant, training students on entrepreneurship.