Eddy-current phenomena in ferromagnetic materials

INTEREST in eddy currents in solid iron masses has kept pace with the development of electromagnetic devices generally.1 The first problems arose in the design of eddy-current brakes for flywheels. Then the use of iron wires for telephone lines and iron rails for the supply of power to a-c locomotives led to new problems. It was recognized that the saturation of the iron was an important factor, and many authors have presented their theories to take saturation into account. Following the appearance of Rosenberg´s work,2 others3¿6 have made an academic problem of substantiating it or elaborating upon it. Recently the damping effect of eddy currents in the solid yokes and pole pieces of d-c machines has become important. Still more recently, it has been recognized that the saturation effect is important in computing the core losses in thin steel or alloy sheets.