Dannatt plates

Dannatt plates - thick sheets made of good electrical conductor (usually copper) positioned around an AC magnetic circuit in order to help in guiding the magnetic flux.^[1]

The alternating magnetic field induces eddy currents in the plates. The orientation of these currents is such as to oppose the magnetic field producing it. As a result the field cannot penetrate through the Dannat plates and is directed along them.

References

1. ^ Philip Beckley, Electrical steels for rotating machines, IET, 2002, ISBN 978-0-85296-980-9, page 289 [1]