Peking University scientists unveil levitating magnetometer for femtotesla-level brain sensing
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Peking University physicists report today in Science a levitating-magnet magnetometer that detects magnetic fields as weak as a few femtotesla. The device, which needs no cryogenics or elaborate shielding, can measure brain activity with a sensor-sample spacing of a few hundred micrometres. The approach is significantly simpler than existing SQUID or SERF technologies.
The Levitating Magnetometer
Wei Ji and colleagues at Peking University suspended a sub-millimeter magnet between a lifting magnet and a diamagnetic material, which stabilizes the sensor via repulsion. A laser reflects off the magnet onto a detector, tracking orientation changes when a sample approaches. The entire setup fits inside a vacuum chamber about the size of a Tupperware box. Magnetic coils and damping systems suppress external noise, enabling detection of fields as weak as a few femtotesla. Ji notes that even a thin aluminium film can introduce 100 femtotesla of interference.
Performance Advantages Over Existing Sensors
The new magnetometer operates at room temperature and without the near-perfect shielding required by spin-exchange relaxation-free (SERF) devices. It is orders of magnitude more sensitive than diamond-based magnetometers and reduces the sample-to-sensor distance to a few hundred micrometres, compared with larger gaps in SQUID-based systems that need cryogenic cooling. The sensor’s sensitivity reaches the femtotesla scale, ten billion times weaker than Earth’s magnetic field.
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