Imposition of sinusoidal flux by feedback for analogue and digital computation of the field distribution in a.c.-magnetised ferromagnetic laminas

The paper gives a method of imposing a sinusoidal flux when computing the electromagnetic Maxwellian field distribution in a lamina which is considered to be plane, and infinite in two directions. The static hysteresis loop has been modelled by a polygonal line. The method has been developed on an analogue computer, and then adapted for digital computation. This avoids the need for iterative computing, and maintains the stability and the convergence achieved with the analogue computation; it also avoids difficulties common to analogue function generators. Both analogue and digital computers need, at the most, one quarter of a period to start computing the steady-state field distribution, and the complete solution is obtained in a single computer run, extended to three quarters of a period only. Agreement between the computed and the measured magnetisation current is poor; it is thought that the main divergence results from the disagreement between the assumed and the actual behaviour of the material. Recognisable, but relatively insignificant, errors result from modelling the hysteresis loop by a polygonal line, and from limitation of the number of steps into which the width of the lamina has been divided.