Design of a Controllable Axial-Flux Halbach Array for Magnetic Suspension Tasks

Magnetic fields enable force application without mechanical connection. By this means, electromagnets apply force across a distance, but require continuous power to maintain constant force. In contrast, switchable permanent magnet mechanisms allow unpowered constant force application, but are typically used in close-range (small gap) applications. Hence, a device enabling low-power force application over greater distances (large gap) is needed. To meet this need, we introduce an adjustable magnetic actuator called a controllable, axial-flux Halbach array (CAHA). The novelty of our design lies in the concentric nesting of two axial-flux Halbach rings. By nesting these rings, the magnetic field extends out axially on one side, with a strength dependent on the relative rotation between the rings. To demonstrate how this mechanism performs in magnetic suspension tasks, we simulated a CAHA design model, compared this design model to alternative magnetic actuators, swept geometric parameters of the design, and empirically characterized a CAHA prototype. Our simulations show that our device required much less power than an electromagnet for low-frequency (<16 Hz) tasks, with an up to 93% reduction in average power for a 5 Hz task. The CAHA model also had force densities up to 2.3x higher than a switchable magnet for large-gap ( $\geq 10$ mm) applications. In empirical tests of the CAHA, magnetic performance closely matched our simulations. These results represent an introduction to the CAHA design that could improve magnetic suspension systems for low-frequency, large-gap applications.