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BELL SYSTEM TECHNICAL JOURNAL 



used in obtaining these curves, does not indicate very small losses 

 readily it is evident that the losses in the perminvar alloy are of a 

 different order of magnitude from those of the other two materials. 

 In order to obtain additional information in regard to the hysteresis 

 loss of this alloy at low flux densities, the sample was measured by 

 the inductance bridge method. It was found that the hysteresis loss 

 at a flux densit}^ of 100 gauss was .024 X 10~^ ergs per cubic centimeter 

 per cycle. The best material in this regard previously known was 

 permalloy, for which a sample containing approximately 78| per cent 

 nickel, measured under similar conditions, had a hysteresis loss of 

 2>2> X 10^^ ergs per cubic centimeter per cycle. 



The growth of the hysteresis loss and the appearance of measurable 

 areas, and the peculiar shapes of the loops for this composition as 

 the flux densities increase are illustrated in Fig. 3. The curve for a 



800 



B 400 



1.2 



Fig. 2 — Hysteresis characteristics: a — Perminvar (45% Ni — 25% Co- 

 30% Fe); h — silicon steel; c — Armco iron 



maximum flux density of 580 gauss in Fig. 3, is from the same data 

 as Curve a in Fig. 2. The circles in this plot indicate points on the 

 ascending branch, and the dots, points on the descending branch. 

 The hysteresis loop broadens out so that it has a measurable area 

 when the maximum flux density is increased to 800 gauss. The 

 existence of a close relation between the hysteresis losses and the 

 constancy of permeability is quite apparent from the permeability 

 curve in Fig. 1 and the curves in Fig. 3. While the permeability 

 remains constant there is practically no hysteresis loss but as it begins 

 to change this loss appears and increases quite rapidly with increase 

 in permeability. The increase in the energy loss and the changes in 

 the shapes of the loops as the flux density increases also are illustrated 

 by these curves. The most striking hysteresis characteristic of these 



