Jumping Ring

This application analyzes the forces generated by the induced eddy-currents in a ring by using the MagNet Transient 2D with Motion solver.

The model is axisymmetric and consists of a coil surrounding the base of a bundle of soft iron wires which may be contained in a non-metallic tube (the latter is not included in this model). The stranded a.c. coil consists of 800 turns, driven by a sinusoidal voltage source with an amplitude of 460 V and a frequency of 50 Hz. The ring is composed of aluminum with conductivity of 3.8e7 Siemens/meter and the core is composed of soft iron with a relative permeability of 1000. The thickness of the ring will affect the induced forces, e.g. a 1/8" ring will float at a reduced height. The solution takes gravity into account.

Results

Click image to see full size version

This flux plot demonstrates the induced current in the ring at 5 ms.

Click image to see full size version

This graph demonstrates the net force on the ring as a function of time. After the first 60 ms the electromagnetic forces are no longer significant so the net force is simply the weight of the ring.

Click image to see full size version

This graph demonstrates the position of the ring as a function of time. After the first 60 ms the ring travels beyond the coil and core, and its trajectory becomes a parabola. The ring will return to its starting position after approximately one second.