Scientists from China’s Shanghai Jiao Tong University have developed a new type of submarine detection for underwater surveillance.

According to its developers, the device can detect even the quietest submarines over an extended range — an accomplishment previously thought to be impossible.

The detection system, which is attached to a surface buoy, is reportedly housed in a large square-like pickup truck structure, and it employs antennas to detect the extremely weak electromagnetic signals that submarine propellers produce.

During tests involving a rotating propeller, the detector identified low-frequency signals at a distance of roughly 12 miles.

“Although a 1.86 miles (3 kms) detection and positioning range is already a significant breakthrough, it still falls short of meeting the requirements for detecting and positioning targets in the open sea,” the researchers noted.

However, the team added that the new technology promises to extend the detection range of those electromagnetic signals to more than 31 miles, which is the distance equal to that of modern torpedoes.

In the past, detecting submarines via electromagnetic signals had been challenging thanks to seawater and its tendency to weaken electromagnetic waves. While propellers cut through the electric fields surrounding navy vessels, they produce electromagnetic radiation, but the signals are short-ranged in seawater.

To combat this, the researchers collected the signals from the seabed instead of receiving them from the water.

The team explained that as a submarine moves, its propellers will rotate once per second, thus creating low-frequency electromagnetic waves that travel into the seabed, spreading along rock layers. Because the waves weaken at a significantly slower rate in the seabed compared to seawater, the detection range is dramatically extended. Specifically, the rate of weakening in the seabed as reported by the team of scientists is just 0.278 decibels per mile versus the higher rate in seawater.

Although this approach is promising, it also presents many challenges — particularly because the electromagnetic waves from the propellers are significantly weaker once they reach the seabed. Further, the seabed is crowded with electromagnetic noise produced by both natural and non-military sources.

To potentially address this, the team built an algorithm that isolates extremely weak signals in the often-noisy seabed environment. Meanwhile, accurate positioning posed another challenge.

To identify a target, the detector requires several high-precision sensors spread across a 0.62-mile area, synchronized with an error margin of no more than a billionth of a second, which is challenging in deep-sea conditions.

The findings were published in the Journal of Vibration and Shock, a Chinese peer-reviewed journal.

To contact the author of this article, email mdonlon@globalspec.com