Fundamental limits to magnetic-field sensitivity of flux-gate magnetic-field sensors

In this letter we determine the theoretical limit of the magnetic-field sen sitivity of the flux-gate magnetometer. In order to do so, we have develope d a model for the white noise of a flux gate based on the fundamental dynam ics of the magnetic material forming the flux-gate core. Solving this model , we predict that the white noise of a physically realizable flux gate with a volume of 2x10(-8) m(3) is less than 100 fT/root Hz. The white noise var ies with the lossy susceptibility of the core and inversely with the volume . We also compare the measured white noise of a thin-film flux gate with th e predictions of our model and find that the measured and predicted noise a gree reasonably well. (C) 1999 American Institute of Physics. [S0003-6951(9 9)03550-0].