1-pT noise fluxgate magnetometer for geomagnetic measurements and unshielded magnetocardiography

Abstract

We present the development of a low-noise, fundamental-mode, orthogonal fluxgate magnetometer with four amorphous, annealed ferromagnetic wires. The 1-Hz noise obtained in open-loop and closed-loop is as low as 0.75 and 1.5 pTrms/√Hz, respectively, with white noise level about 0.6 pTrms/√Hz. This is to our knowledge the lowest figure published for a fluxgate magnetometer so far. We compared the instrument performance to a low-noise observatory magnetometer when doing geomagnetic measurements and show that it is fully suitable for measurements at mHz frequencies, e.g. magnetotellurics. The magnetometer performance enables room-temperature, unshielded magnetocardiography.