Bandwidth enhanced current noise suppression with a SERF magnetometer

TL;DR

This paper presents a feedback-controlled SERF magnetometer system that significantly enhances bandwidth and suppresses current noise, achieving sub-nanoampere noise levels and promising high-precision current sensing.

Contribution

It introduces a novel feedback configuration with an injection transformer for SERF magnetometers, greatly improving noise suppression and bandwidth over traditional open-loop setups.

Findings

Bandwidth increased by nearly two orders of magnitude.

Current noise reduced below 3 nA/√Hz across broad frequencies.

Potential sensitivity of a few pA/√Hz if technical noise is eliminated.

Abstract

This work investigates the behavior of a spin-exchange relaxation-free (SERF) magnetometer integrated into the feedback branch of a closed-loop control circuit, designed to actively suppress noise from a current source. In this configuration, the magnetometer bandwidth is enhanced by almost two orders of magnitude as compared to the open-loop setup. Incorporating an injection transformer, the proposed system effectively reduces current noise to below 3 nA/sqrt(Hz) over a broad frequency bandwidth, independent of DC-current offsets. Analysis of the system sensitivity reveals that the performance is currently limited by technical noise. If this were to be eliminated, the system would achieve a current sensing sensitivity on the order of few pA/sqrt(Hz), while maintaining perfect galvanic isolation from the target circuit.