Suppression of Magnetic Noise and Field in Cubic Low-Noise Ferrite Magnetic Shields

Abstract

Most magnetic shielding rooms (MSRs) are made of highly permeable permalloy. The limitation of such MSR is its intrinsic magnetic noise exceeds the sensitivity of magnetic sensors, impeding the further applications of ultrasensitive magnetic sensors, such as the magnetometers operated in the spin-exchange relaxation free (SERF) regime. In this article, a cubic ferrite magnetic shield with a low magnetic noise and magnetic field is proposed. The demagnetization model and magnetic noise calculation models are given. After optimizing several different coil structures and degaussing parameters, the magnetic field and the magnetic noises inside the cubic ferrite shield were measured. Within a distance of ±10 mm near the center, the residual magnetic field is below 0.5 nT, 1.72 nT and 1.57 nT at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> directions. The magnetic noise measurements at the center of the cubic ferrite magnetic shield reveal an averaged magnetic noise of 2.62 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> from 20 Hz to 100 Hz. Compared with the noise spectrum of permalloy shield, the noise level is reduced more than 133%. The results of this scaled-down cubic ferrite magnetic shield can be applied in larger sized shielding rooms. By assembling multiple ferrite panels together, it is possible to create a larger shielding space with a low magnetic field and low magnetic noise.