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This paper studies the behavior of rotating magnetic microrobots, constructed with a permanent magnet or a soft ferromagnet, when the applied magnetic field rotates faster than a microrobot's step-out frequency (the frequency requiring the entire available magnetic torque to maintain synchronous rotation). A microrobot's velocity dramatically declines when operated above the step-out frequency. As a result, it has generally been assumed that microrobots should be operated beneath their step-out frequency. In this paper, we report and demonstrate properties of a microrobot's behavior above the step-out frequency that will be useful for the design and control of multi-microrobot systems.
Mahoney et al. (Mon,) studied this question.