Reactance sensors of radial position for magnetic bearings and bearingless drives

A radial position sensor includes a rotating element configured to rotate about an axis of rotation, which subject to displacement. The displacement from a first position to a second position can be represented by polar coordinates, e.g., (ρ, φ), where ρ is a distance and φ is an angle. The sensor also includes a non-rotating emitting element configured to provide a plurality of electromagnetic fields and a non-rotating receiving element configured to receive the plurality of electromagnetic fields. The plurality of electromagnetic fields are electromagnetically coupled to the non-rotating receiving element through the rotating element. The electromagnetic coupling varies in dependence on the radial position of the axis of rotation of the rotating element. The non-rotating receiving element produces an output signal in response to the amount of coupling of the plurality of electromagnetic fields, and so the output signal is an indication of the radial position of the axis of rotation.