Scientists have turned a levitating magnet into a magnetometer sensitive enough to detect the faint magnetic signals of the brain's electrical activity — with a design far simpler than today's state-of-the-art instruments. The work is reported today in Science by physicist Wei Ji and collaborators at Peking University.
At the device's heart is an exquisitely sensitive compass needle less than a millimetre in size: a tiny permanent magnet suspended between a lifting magnet above it and a diamagnetic stabilizer below, probed by a laser beam inside a vacuum chamber about the size of a lunchbox.
The most sensitive existing magnetometers either need cryogenic cooling (SQUIDs) or near-perfect magnetic shielding (SERF magnetometers). The levitating design sidesteps both, shrinks the gap between sample and sensor to a few hundred micrometres, and is orders of magnitude more sensitive than diamond-based magnetometers.
Noise control is extreme at this scale. "When you're probing the femtotesla scale, even a thin film of aluminium foil can introduce 100 femtoteslas of noise," says Ji — a femtotesla being ten billion times weaker than Earth's magnetic field.
Beyond biophysics, the team says the instrument could one day be used to hunt for dark matter, making a lunchbox-sized magnet one of the most promising new eyes on both the brain and the universe.
