For US submarines operating in waters near China, the era of absolute stealth may be ending – one magnetic ripple at a time.
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Researchers with Northwestern Polytechnical University (NPU) in Xian claim to have developed a groundbreaking method to detect even the quietest underwater vessels by harnessing the magnetic fields generated by their wakes – a discovery that could reshape naval warfare.
Led by associate professor Wang Honglei, the team modelled the Kelvin wake, a V-shaped surface disturbance created by submarines as they slice through water. This wake, previously studied for radar-based imagery detection, generates a faint but detectable magnetic field when seawater ions – disturbed by the vessel’s motion – interact with Earth’s geomagnetic field.
Using numerical simulations, the researchers quantified how these magnetic signatures vary with a submarine’s speed, depth and size. For example, increasing speed by 2.5 metres per second (8.2 feet per second) boosts magnetic intensity tenfold; reducing depth by 20 metres (66 feet) doubles the field strength; and longer submarines produce weaker fields, while wider hulls amplify them.
For a Seawolf-class submarine travelling at 24 knots (12.5 metres per second) and 30 metres (98 feet) depth, the wake’s magnetic field reaches 10⁻¹² tesla – “well within the sensitivity range of existing airborne magnetometers,” according to Wang and his colleagues.
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The team’s method, which was detailed in the peer-reviewed Journal of Harbin Engineering University on December 4, exploits a critical vulnerability: “Kelvin wakes cannot be silenced.”