### Abstract

Stability of a solid sphere in both uniform and linear alternating magnetic fields is considered with respect to virtual rotations. When the frequency of the alternating magnetic field exceeds a certain critical threshold depending on the configuration of the field, the sphere is found to spin up around a horizontal axis. The physical mechanism of this instability is the same as that of operation of a single-phase induction motor. Sufficiently small rotational disturbances can be completely suppressed by imposing an axial steady magnetic field of strength comparable to that of the alternating field. Nonlinear stability analysis shows that for sufficiently high frequencies, spin-up can be caused by large disturbances even when all infinitesimal disturbances are stable.

Original language | English |
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Pages (from-to) | 349-353 |

Number of pages | 5 |

Journal | IEEE Transactions on Magnetics |

Volume | 36 |

Issue number | 1 PART 2 |

DOIs | |

Publication status | Published - Jan 2000 |

Externally published | Yes |

### Keywords

- Electromagnetic forces
- Magnetic lévitation
- Stability
- Magnetic fields
- Frequency
- Solids
- Magnetic analysis
- Heating
- Induction motors
- Stability analysis
- Conductors
- Coils
- electromagnetic forces
- magnetic levitation
- mechanical stability
- infinitesimal disturbances
- spin-up instability
- electromagnetically levitated spherical bodies
- solid sphere
- uniform alternating magnetic fields
- linear alternating magnetic fields
- virtual rotations
- critical threshold
- horizontal axis
- rotational disturbances
- axial steady magnetic field
- nonlinear stability analysis

### ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering

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## Cite this

*IEEE Transactions on Magnetics*,

*36*(1 PART 2), 349-353. https://doi.org/10.1109/20.822545