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BELL SYSTEM TECHNICAL JOURNAL 



is a, the eddy current coefficient e, and the residual loss term is c. 

 W is the energy loss per cycle in ergs/cm^ of core material. The 

 permeability coefficient X = (mw — noJlfxoBm. 



Table I shows that annealed 35 permalloy in sheet form has the most 

 convenient values of Br and c/a for further study of this effect. This 

 alloy is of the face centered cubic lattice type common to a large class 

 of magnetic alloys. The numerals preceding the various permalloys 

 give the nickel or alloy percentages, as classified by G. W. Elmen.^ 



The measurement of magnetic losses of 35 permalloy involved further 

 refinements in technique. The high initial permeability required the 

 construction of a special air core mutual inductance to simplify the 



TABLE I 



* These values of remanence were computed from Rayleigh's law as 3aiJi.oB,J/l6 

 for Bm = 2. 



measuring circuit and increase its stability. The high rate of change 

 of permeability with temperature made it necessary to enclose both 

 the specimen and the air core mutual inductance in a constant tem- 

 perature box (at 37.1 ± 0.01° C.) throughout the tests. 



The Specimen 



The material was melted in a high-frequency furnace, cast, and 

 cold-rolled with intermediate annealings, to strip of thickness 

 / = 0.0160 cm. and width 7.62 cm. Analysis showed the following 

 composition; Ni, 35.00 per cent; Fe, 64.25 per cent; Mn, 0.40 per cent; 

 S, 0.030 per cent; Si, 0.02 per cent; C, 0.01 per cent. The resistivity p 

 was 82.2 micro-ohm-cms. at 37.1" C. The strip was wound into a tight 



^ Electrical Engineering, 54, 1292 (1935). 



