{A photograph} of a black graphite disk floating above a stack of three, spherical magnets. (Credit: Adrian Skov (OIST))
Study reveals how excellent magnetic symmetry can cancel vitality loss.
In A Nutshell
- Researchers at OIST constructed a 10-millimeter graphite disk that levitates and spins above a magnetic array inside a vacuum chamber.
- By arranging magnets in excellent round symmetry, the setup cancels the eddy currents that usually sluggish conductors transferring via magnetic fields.
- Even at one-billionth of Earth’s air strain, the disk stored spinning with nearly no slowdown; solely tiny tilts or materials imperfections created measurable friction.
- This ultra-stable, contact-free rotor may allow new sorts of gyroscopes, vacuum gauges, and precision devices to check gravity, quantum results, or “vacuum friction.”
OKINAWA, Japan — A small graphite disk floats in midair, spinning freely above a hoop of magnets inside a vacuum chamber. There’s no bodily contact, no vitality being pumped in, but it retains rotating with nearly no slowdown, behaving in ways in which appear to defy on a regular basis friction, however observe exact bodily guidelines.
Researchers on the Okinawa Institute of Science and Technology have achieved what appears nearly magical: a conducting rotor that levitates and spins with terribly low energy loss. Published in Communications Physics, the research demonstrates a 10-millimeter disk manufactured from pyrolytic graphite that hovers above everlasting neodymium magnets, spinning in near-perfect isolation from the forces that usually carry rotating objects to a halt.
The secret lies in a cautious association. By utilizing magnets positioned in a sample the place the magnetic field seems an identical from each angle round a central axis, the researchers eradicated a serious supply of vitality loss known as eddy damping. When most conductive supplies spin in magnetic fields, they generate electrical currents that act like brakes. In this setup, the symmetry means these currents by no means kind.
Graphite That Pushes Back Against Magnets
Pyrolytic graphite is a peculiar materials. Unlike most substances, it actively repels magnetic fields. Place it above the best association of magnets, and it pushes again arduous sufficient to levitate at room temperature with none energetic management or energy provide.
The analysis staff constructed a magnetic lure from 5 layers of ring-shaped magnets surrounding two central cylinders. Each layer alternated north and south poles to create a secure discipline that held the graphite disk about 0.82 millimeters above the floor.
To observe the disk’s rotation, researchers marked its floor with a white dot of ink and filmed it with a specialised digicam that detects movement. Even at pressures close to 5 × 10⁻⁵ Pascals (roughly a billionth of atmospheric strain) the disk stored spinning with barely any slowdown.
What Normally Stops a Spinning Object
At regular air strain, the disk’s rotation slows primarily as a result of air molecules collide with it. Higher strain means extra collisions and sooner slowdown.
The researchers measured how rapidly the disk’s spin decayed at completely different pressures, from atmospheric ranges right down to near-vacuum situations. At excessive pressures, gas collisions dominated. In intermediate ranges, the damping price scaled linearly with strain, precisely as concept predicted for molecules bouncing off the floor.
At very low pressures although, one thing else took over. Even when gasoline molecules turned sparse sufficient that they not often hit the disk, a small quantity of damping continued beneath about 0.1 Pascals.
The Surprising Culprit: A Tiny Tilt
That residual damping got here from imperfect symmetry. When the experimental platform tilted even barely, as little as a fraction of a level, gravity pulled the disk’s heart of mass off the magnetic discipline’s central axis. Once offset, the disk’s rotation did generate small eddy currents as a result of completely different elements of the disk skilled completely different magnetic discipline strengths as they spun previous.
To examine this, the staff intentionally tilted their setup at numerous angles whereas preserving the strain fixed. The damping price elevated dramatically with tilt, climbing by an order of magnitude inside half a level of offset from excellent stage. The researchers confirmed that damping will increase roughly with an influence regulation of the disk’s lateral offset from excellent alignment.
Computer simulations confirmed this sample. The simulations confirmed that for displacements better than 0.05 millimeters from the symmetry axis, the damping adopted a near-perfect power law relationship. Extrapolating backward, the info pointed strongly to eddy damping vanishing solely at precisely zero displacement, the place excellent symmetry exists.
Mathematical Proof of a Frictionless Spin
To affirm their observations, the researchers proved mathematically {that a} conductor rotating in a superbly symmetric magnetic discipline can not maintain regular eddy currents, as a result of each level experiences an unchanging magnetic flux.
Without altering magnetic flux, there’s nothing to induce electrical currents. The staff additionally constructed an express instance with a selected magnetic discipline geometry the place they calculated the currents straight and confirmed they vanished.
Computer simulations alone couldn’t fairly attain zero damping as a result of the computational grid inevitably breaks excellent symmetry at microscopic scales. The mathematical work eliminated any lingering doubt.
The measured minimal damping price within the experiment was 5.5 × 10⁻⁵ Hz, equivalent to an offset of about 18 micrometers from excellent alignment. That tiny displacement doubtless arose from slight imperfections in both the graphite disk or the magnets themselves.
When Symmetry Breaks, Energy Bleeds
When researchers levitated the identical disk on a unique magnet association — a checkerboard sample as a substitute of the cylindrical array — the disk’s rotation damped out quickly despite the fact that its form was equally round. The checkerboard’s lack of rotational symmetry meant each level on the spinning disk repeatedly skilled altering magnetic fields, producing energy-sapping eddy currents all through.
Material inhomogeneities may additionally break symmetry. Pyrolytic graphite has completely different properties alongside completely different crystal instructions, and if the disk’s geometric heart doesn’t align completely with its materials symmetry axis, related offsets happen.
From Laboratory Curiosity to Real-World Tools
A rotor that spins nearly indefinitely with out contact has sensible purposes. Gyroscopes primarily based on this precept may obtain unprecedented sensitivity for detecting rotations, probably measuring Earth’s spin or tiny angular accelerations in spacecraft navigation.
Pressure sensors already use spinning rotors to gauge vacuum ranges in ultra-high vacuum chambers. Lower damping means higher sensitivity to the few remaining gasoline molecules that trigger the slowdown.
The setup may additionally probe fundamental physics. Researchers have proposed utilizing macroscopic spinning objects to check quantum mechanics at massive scales or to seek for delicate results like vacuum friction—the concept empty house itself would possibly exert a tiny drag on rotating objects.
Getting the symmetry much more excellent would push the boundaries additional. The researchers famous that higher fabrication strategies like laser chopping or electrical discharge machining may produce extra geometrically exact disks, whereas utilizing supplies like bismuth with greater crystalline high quality would possibly scale back material-induced asymmetries. With higher machining and exact tilt management, they estimate damping may drop to about 10⁻¹¹ Hz, so low the disk would possibly spin for weeks with nearly no vitality loss.
Paper Summary
Methodology
The researchers fabricated a ten.02-millimeter diameter, 1.12-millimeter thick disk from pyrolytic graphite utilizing pc numerical management milling adopted by diamond sharpening to make sure excessive circularity. They created a magnetic lure utilizing 5 layers of ring-shaped neodymium magnets surrounding two cylindrical magnets on the heart, organized with alternating vertical magnetization. The graphite disk levitated about 0.82 millimeters above this array inside a vacuum chamber able to reaching pressures close to 5 × 10⁻⁵ Pascals. To measure rotation, they marked the disk’s floor with white ink and tracked it utilizing an event-based digicam viewing the disk via a mirror and telescope lens association. They induced rotation via lateral vibrations and measured how the angular velocity decayed over time at completely different gasoline pressures. They additionally systematically various the platform’s tilt angle utilizing optical desk changes and screw jacks whereas measuring the ensuing adjustments in rotational damping.
Results
At atmospheric strain, rotational damping was dominated by gasoline friction following laminar circulate dynamics, with finite aspect simulations matching experimental observations. As strain decreased into the free molecular circulate regime (beneath 100 Pascals), the damping price scaled linearly with strain, agreeing with theoretical predictions for ballistic molecule collisions. Below roughly 0.1 Pascals, damping reached a plateau round 10⁻² Hz regardless of additional strain reductions. Tilt experiments revealed that this residual damping elevated dramatically with platform inclination, climbing by an order of magnitude inside 0.5 levels of tilt from the minimal damping orientation. The minimal noticed damping price was 5.5 × 10⁻⁵ Hz, equal to an 18-micrometer offset from excellent axial symmetry primarily based on the fitted energy regulation relationship between displacement and damping. Finite aspect simulations of eddy damping confirmed near-perfect energy regulation dependence for offsets better than 0.05 millimeters, with the connection extrapolating to zero damping at zero displacement. Mathematical proofs demonstrated that the steady-state present density in a uniformly rotating conductor inside a superbly symmetric magnetic discipline have to be precisely zero.
Limitations
The research confronted a number of constraints associated to attaining excellent symmetry. The minimal measured damping price was restricted by small geometric or materials imperfections in both the pyrolytic graphite disk or the magnet meeting. Slight misalignments between the disk’s geometric heart and its materials symmetry axes may introduce asymmetry. Finite aspect simulations turned unreliable for displacements beneath 0.05 millimeters attributable to mesh-induced asymmetry and numerical errors, stopping direct computational verification of zero damping at excellent alignment. The experimental setup had an preliminary platform misalignment of roughly 0.5 levels that needed to be corrected. The fabrication course of, whereas exact, might not have achieved completely uniform materials properties all through the disk. Environmental vibrations or thermal fluctuations may dynamically displace the disk from the symmetry axis, although calculations confirmed thermal results at room temperature would contribute negligible damping (round 10⁻¹⁵ Hz). The research didn’t take a look at supplies with greater crystalline high quality than pyrolytic graphite or make use of superior fabrication strategies like laser chopping or electrical discharge machining that may additional scale back asymmetries.
Funding and Disclosures
This work was supported by the Okinawa Institute of Science and Technology Graduate University in Japan. The authors acknowledged help from the Engineering Section and the Scientific Computing and Data Analysis Section at OIST. The authors declared no competing pursuits.
Publication Details
Kim, D., Tian, S., Calderoni, B., Sastre Jachimska, C., Downes, J., & Twamley, J. (2025). A magnetically levitated conducting rotor with ultra-low rotational damping circumventing eddy loss. Communications Physics, 8, 381. DOI: 10.1038/s42005-025-02318-4