1957a
The following is a paper by H. Aspden published by the Institution of
Electrical Engineers as Monograph No. 187M (July 1956) and later in Proc. I.E.E.
vol. 104C at pp. 2-7 (1957).
AN INVESTIGATION OF THE EDDY-CURRENT ANOMALY IN A LOW-SILICON SHEET
STEEL
Abstract: The eddy-current anomaly effects in a 0.019 in
thick low-silicon sheet steel are investigated and analysed on the basis of
magnetic inhomogeneity arising from ferromagnetic domain structure. This
particular steel was chosen because previous experimental work had shown that
inherent time-lag effects in the magnetization process were small. However, in
such steel, flux waveform distortion arising from hysteresis phenomena adds to
the anomaly effect, and a special experimental technique by which such
distortion effects could be eliminated from the analysis was developed. This
made it possible to test the magnetic inhomogeneity. The results obtained were
interpreted in terms of a hypothetical domain configuration, and it is concluded
that the magnetic inhomogeneity arising from ferromagnetic domain structure does
account for the eddy-current anomaly, distortion and time-lag effects being of
minor importance.
Commentary: The advance reported in this paper
was the step of measuring the eddy-current loss anomaly factor, not as an
averaged effect taken over a full cycle of magnetization, but rather as an
incremental effect confined to the rising portion of the flux density range. The
effective permeability over the relevant range of magnetization is linear and it
was found that the anomaly effect was concentrated over this range of
magnetization, rather than the region at the top and falling portion of the B-H
loop. What this meant was that one could see how quite large anomaly factors at
levels hardly justified by magnetic domain inhomogeneities were in
evidence.
See the related papers: [1956a]
and [1956b].
