Tiny levitating magnet detects ultrafaint magnetic fields at room temperature
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Researchers have developed a miniature levitating magnet that detects magnetic fields as faint as 32 femtoteslas per square root of Hertz at room temperature, a study in Science reports. The device floats in a vacuum chamber, uses a laser to sense tilt, and cuts thermal magnetic noise by more than 70% through a graphite-epoxy plate.
The Levitating Sensor
The sensor consists of a permanent magnetic disk smaller than a grain of rice, suspended inside a glass vacuum chamber. An overhead stack of magnets pulls the disk upwards against gravity, while a graphite plate beneath provides repulsive stabilization. A continuously shining laser beam reflects off the disk’s surface; when an external field tilts the magnet, the beam’s shift is detected and converted into an electrical signal.
Sensitivity Measurement
The team generated weak artificial fields using wire coils around the chamber to test performance. The device achieved a sensitivity of 32 femtoteslas per square root of Hertz, a level that can detect brain and heart magnetic signals normally requiring cryogenic cooling. This sensitivity is recorded without the need for shielded rooms or liquid helium.
Thermal Noise Reduction
A key innovation is the lower graphite plate made from powdered graphite bound in epoxy. This material cut Johnson noise — random thermal charge movements — by more than 70% compared to conventional sensors. The suppression allows the floating magnet to pick up far weaker signals at room temperature, sidestepping a major limitation of existing magnetometers.
What's Next
The device is now poised for real-world testing in biomedical and physics applications; the team plans to integrate it into portable systems. It remains unclear how quickly the technology can be commercialized or scaled for widespread use.
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Tiny levitating magnet detects ultrafaint magnetic fields at room temperature
