A magnetic amplifier for the visual presentation of low-frequency hysteresis loops of very small ferromagnetic samples

This paper describes a magnetic amplifier based on the principle of permeability tuning, and intended for the amplification of small, low-impedance signals obtained from a small ferromagnetic sample (e.g., a ferrite memory core or a thin film). The apparatus is able to produce a good display of a flux as low as
\Delta\phi = 10^{-12}
V/s at 50 c/s. In this case, the signal power applied to the amplifier is of the order of 10
^-16
watts.