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Zhang Tong

Picture a fisherman hauling in his nets on a calm morning at sea, when his smartwatch suddenly vibrates with an alert: “Magnetic anomaly detected – possible submarine passing 500 metres below.”
Far‑fetched as it sounds, Chinese scientists have just taken a decisive step towards making that scenario real.
A team from the Hefei Institutes of Physical Science and the Ningbo Institute of Materials Technology and Engineering, both under the Chinese Academy of Sciences (CAS), has created a Hall‑effect magnetic sensor so sensitive that it could, in theory, pick up the faint magnetic shadow of a steel‑hulled submarine from half a kilometre (1,640 feet) away – all within a chip no bigger than a grain of dust.
Their findings, published on July 17 in the journal Physical Review Letters, shatter a decades-old sensitivity-versus-noise trade-off that has kept everyday magnetic sensors from hearing the quietest signals.
Hall‑effect sensors are the unsung workhorses inside many everyday gadgets. Already built into smartwatches, smartphones, car wheel‑speed detectors and hospital scanners, they detect magnetic fields by generating a tiny voltage when a field is present. They are simple, cheap, fast and compact – perfect for wearables.
But until now, shrinking them and making them more sensitive came with a punishing side‑effect: more noise, much like cranking up a radio’s volume also amplifies the hiss.
Inside magnetic materials, countless electrons spin and form patterns called spin textures. These patterns are far from static – they ripple, oscillate, and sometimes abruptly flip from one state to another. That microscopic motion produces noise at the macroscopic scale.
The team found that the noise level depends directly on how fast the textures move: slower motion creates more noise, faster motion creates less, and the two are linked by a precise inverse relationship.
Building on this insight, they designed an artificial ferromagnetic structure with exceptionally rapid spin texture dynamics. By precisely controlling the thickness of the magnetic layers and fine-tuning the annealing process, they maximised the material’s sensitivity to magnetic fields.
The resulting anomalous Hall magnetic sensor, based on this new material, has an effective detection area of just 20 by 20 micrometres.


Unlike bulky proton magnetometers that guzzle power or superconducting quantum interference devices (SQUIDs) that need expensive cooling, Hall-effect sensors are significantly cheaper and simpler to use.
The researchers said in the paper that this method could also work with other magnetic materials. Some of these may have even faster internal spin dynamics, which could slash noise even further – by several orders of magnitude.
So could this technology be used to detect submarines? In principle, yes, though practical deployment still faces many challenges.
Submarine detection is a key application of magnetic anomaly detection (MAD) technology. Steel-hulled submarines moving through the Earth’s magnetic field act like moving magnets, disturbing the local field distribution. The sensor’s job is to pick up the submarine’s faint anomaly.
The current sensor sensitivity in this study could detect a submarine at close range, but it still falls short for long-range detection. While anti-submarine warfare remains a distant goal, the technology holds more immediate promise in biomedical and industrial applications.
The human heartbeat produces magnetic signals, and brain neural activity generates its own magnetic fields. These signals typically fall within the picotesla to nanotesla range – right within the operating window of this new sensor.
Combined with its tiny detection area of just 20 micrometres, the device could provide new tools for brain science research and early diagnosis of heart conditions.
“In the automotive industry, electronics manufacturing and materials science, this high-sensitivity, low-noise, compact sensor could also be used in scanning probe microscopy to image the microscopic structure of materials,” according to CAS.


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Compact chip containing Hall-effect sensor can pick up faint magnetic fields by generating a tiny voltage without increasing noise output


Compact chip containing Hall-effect sensor can pick up faint magnetic fields by generating a tiny voltage without increasing noise output.


Chinese Academy of Social Sciences

Chinese magnetic sensor breakthrough may help smartwatch detect submarine 500 metres deep

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Compact chip containing Hall-effect sensor can pick up faint magnetic fields by generating a tiny voltage without increasing noise output

Compact chip containing Hall-effect sensor can pick up faint magnetic fields by generating a tiny voltage without increasing noise output