10 times more sensitive: China’s tiny sensor could detect submarines from 1,640 feet away

Chinese scientists have developed an ultra-sensitive, low-noise magnetic sensor capable of detecting extremely weak magnetic fields. This new sensor could, in theory, be used for submarine detection or biomedical devices. The new sensor takes advantage of something called the Hall effect, which, the team behind it claims, can better distinguish a weak magnetic signal from its own “internal noise.” Interestingly, the new sensor, the team explains, is small and compact, meaning it could be integrated into small electronics like a smartwatch. These kinds of sensors work by detecting tiny changes made when an electrical current is passed through a magnetic field. Any deflection of electrons shows up as a tiny, almost imperceptible change in voltage. So, the stronger the magnetic field, the larger that voltage change becomes. Hall-effect sensors like this are attractive because they’re tiny, cheap, solid-state, and easy to put on chips. In theory, the new magnetic sensor can detect the faint magnetic signature of a steel-hulled submarine up to half a kilometer (1,640 feet) away, as reported by SCMP. New noise-reducing Hall-effect sensor The trouble is that when you make them extremely sensitive, the magnetic material itself starts producing fluctuations that look like a real signal. In other words, you turn the gain up and hear more hiss (AKA noise). To get around this, the joint team from the Hefei Institutes of Physical Science and the Ningbo Institute of Materials Technology and Engineering took advantage of something they call “spin-texture dynamics.” To understand what this means, it is important to conceptualize what happens inside a magnetic material. Rarely, if ever, are magnetized materials uniform in polarity throughout them. More often, they consist of regions and patterns of magnetization with domains, boundaries, and other structures in 3D. What’s more, these are rarely constant, often fluctuating over time. You can liken it to a field of long grass blowing in the wind. Each blade of grass represents electron spins, with large patches of grass leaning in the same direction representing a domain. When the wind blows, ripples form in the grass field, which, in this analogy, would represent changes in magnetic texture. In real magnetic materials, these microscopic changes contribute to what is called magnetic noise. Some interesting applications Knowing this, the team found that the faster these magnetic textures evolve, the lower the low-frequency noise of the sensor can become. They therefore engineered a multilayer magnetic material (called a synthetic ferrimagnet) whose spin textures move particularly rapidly. That, the team explains, lets them retain a strong Hall response to an external magnetic field while substantially suppressing the unwanted fluctuations. According to the team, the resulting sensor has an active area of only 20 by 20 micrometers (about the size of a human skin cell) and achieved a field detectability of about 15.7 nanotesla/√Hz at 1 Hz. The team reports that as nearly an order-of-magnitude improvement over previous comparable ferromagnetic Hall sensors. While reports claim this could, in theory, be used to detect a nearby submarine, the team itself is more conservative, stating that it could have automotive, biomedical, and magnetic microscopy applications. For example, it could be used for things such as extremely compact cardiac magnetic imaging, brain-field measurements, lab-on-chip biological sensors, and very high-resolution magnetic microscopy. The authors also argue that the underlying noise relationship should apply to other magnetic materials, and they are confident that faster spin dynamics could potentially push the noise down considerably further. Get the latest in engineering, tech, space & science - delivered daily to your inbox.Christopher graduated from Cardiff University in 2004 with a Masters Degree in Geology. Since then, he has worked exclusively within the Built Environment, Occupational Health and Safety and Environmental Consultancy industries. He is a qualified and accredited Energy Consultant, Green Deal Assessor and Practitioner member of IEMA. Chris’s main interests range from Science and Engineering, Military and Ancient History to Politics and Philosophy.