Self-balancing flux-gate magnetometers

This paper is concerned with the application of the self-balancing magnetic-amplifier technique in the realm of flux-gate magnetometers. It describes a second-harmonic type of self-balancing flux-gate magnetometer which is operated in conjunction with a push-pull magnetic amplifier in such a way that the d-c flux in the high-permeability cores of the magnetometer is completely balanced by an opposing d-c flux. Thus, the magnetic field to be investigated, e.g., the earth's field in the vicinity of the magnetometer, remains substantially undisturbed. The compensating d-c flux is linearity proportional to the average value of the polarity-reversible unidirectional output current of the magnetic amplifier. With infinite internal gain (“critical regeneration”), this current is varied by an infinitesimal d-c flux increment in the cores of the magnetometer and may be indicated and/or recorded by means of high-precision moving-coil instruments or d-c potentiometer recorders. In a modified arrangement, the self-balancing flux-gate magnetometer is used as a “gradiometer” for measurement of inhomogeneity of magnetic fields.