CST – Computer Simulation Technology

Eddy Current and Proximity Effect | The Jumping Ring Experiment

This article serves to demonstrate the ability to take into account skin and proximity effects in conducting coils. A simple model of the jumping ring experiment, described in [1], is ideal for this purpose and provides an insight into the physics involved in the problem. Quantities such as induced voltages, self and mutual inductances can be calculated in the CST EM STUDIO® low frequency eddy current solver.

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Figure 1: Jumping ring model setup

Figure 1 shows the set up of the model of a jumping ring arrangement. The rings are made of aluminium. Inserted into each of the rings are current segments which allow either the current to be injected, as in the lower ring, or, to be measured as in the upper two rings. The measurement segments can be used to extract the inductance and other parameters....



Figure 2: Current density plot clearly showing the Skin and proximity effect

Two approaches are available for dealing with eddy current effects. The conductor may be meshed in order to capture the skin and proximity effects with, as a rule of thumb, at least 2-3 mesh cells per skin depth. This approach is appropriate if the user is interested in visualizing the behavior of the eddy currents in the conductor. However, this choice is affected by the dimensions and the skin depth. If the skin depth becomes extremely small, then another approach is required. A so-called Surface Impedance approximation may be applied which is based on the analytical behavior of the eddy currents within the conductor. In this example, the skin effect may be captured well with an appropriate mesh. The results are shown in figure 2 in which the skin and proximity effects are clearly visible.

References

[1] Davey, K. R. and Zheng, D.,“Prediction and Use of Impedance Matrices for Eddy-Current Problems”, IEEE Trans.on Magn., vol. 33 pp. 2478-2485, 1997.

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