Floating Ring
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This application analyzes the forces generated by the induced eddy-currents in a ring by using the MagNet Transient 2D with Motion solver. The position of the ring stabilizes when all the forces are equal.
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 230 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 solution takes gravity into account.
Results
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This is a snapshot of the flux plot at 5 ms. The flux plot clearly demonstrates the effect of the induced currents in the ring.
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After the initial transient condition, which occurs when the power is switched ON, the levitation force cancels out the gravitational force on the ring resulting in a very small net force oscillating near zero.
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As can be seen in the illustration to the right, the ring jumps to a height of 21 cm (in 250 ms) above the coil, and then descends to a height of about 13 cm. It finally stabilizes and remains at a height of 15 cm when the levitation force on the ring cancels out the gravitational force.