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Sci Adv. 2018 Jan 5;4(1):e1701519. doi: 10.1126/sciadv.1701519. eCollection 2018 Jan.

Ultrafast rotation of magnetically levitated macroscopic steel spheres.

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Power Electronic Systems Laboratory, Swiss Federal Institute of Technology, Technoparkstrasse 1, 8005 Zurich, Switzerland.
Levitronix GmbH, Technoparkstrasse 1, 8005 Zurich, Switzerland.


Our world is increasingly powered by electricity, which is largely converted to or from mechanical energy using electric motors. Several applications have driven the miniaturization of these machines, resulting in high rotational speeds. Although speeds of several hundred thousand revolutions per minute have been used industrially, we report the realization of an electrical motor reaching 40 million rpm to explore the underlying physical boundaries. Millimeter-scale steel spheres, which are levitated and accelerated by magnetic fields inside a vacuum, are used as a rotor. Circumferential speeds exceeding 1000 m/s and centrifugal accelerations of more than 4 × 108 times gravity were reached. The results open up new research possibilities, such as the testing of materials under extreme centrifugal load, and provide insights into the development of future electric drive systems.

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