Study of Magnetic Losses at Low Flux Densities in Permalloy Sheet

for an the excessive magnetic losses THE search atcomparedexplanation of by indications based on directobserved low flux densities alternating current bridge measurement as with theoretical current measurements has led to a more accurate review of both types of measurement. - The a.-c. energy loss per cycle which has re1,2 3 2 * To be published in May 1937 issue of Jour, of Applied Physics. W. B. Ell wood, Physics, 6, 215 (1935). V. E. Legg, Bell Syst. Tech. Jour., 15, 39 (1936). ' W. B. Ellwood, Rev. Set. Inst., 5, 301 (1934). 1 212 MAGNETIC LOSSES AT LOW FLUX DENSITIES 4 213 ceived most study is the "residual" or "viscosity" loss. It appears related to hysteresis loss because it is nominally independent of frequency, but it differs in being proportional to B instead of B which would be required by Rayleigh's law for hysteresis loops. Any satisfactory investigation of this anomalous loss demands precise determination of its value, and of its variation with frequency. For this purpose, ballistic galvanometer measurements of the hysteresis loop have been made and compared with bridge measurements of a well annealed 35 permalloy laminated core. In a previous paper, the magnetic properties of a ring of compressed powdered iron were studied at low flux densities using a sensitive vacuum galvanometer and a multiple swing ballistic method. Hysteresis loops were measured at flux densities B ranging from 1.8 to 115 gauss, which showed energy losses proportional to B in accordance with Rayleigh's law.