Frequency-dependent amplitude correction to free-precession scalar magnetometers

TL;DR

This paper reveals a frequency-dependent non-linearity in free-precession scalar magnetometers' response and introduces an analytic correction method to improve measurement accuracy, especially near Nyquist frequency, enhancing applications like magnetoencephalography.

Contribution

It provides the first analytic correction for frequency-dependent amplitude response in scalar magnetometers, accounting for dead-time effects and spectral density correction.

Findings

Maximum amplitude loss approaches 29% at Nyquist frequency

The correction improves sensor response accuracy across bandwidth

Proposed scheme identifies out-of-band signals via variable dead-time fits

Abstract

Pump and probe scalar atomic magnetometers show incredible potential for real-world, traditionally difficult measurement environments due to their high dynamic range and linearity. Previously, it has been assumed these scalar magnetometer have a flat response across their bandwidth, and flat noise floor. Here we show that standard fitting routines, used to extract the magnetic field, result in a non-linear frequency dependent response across the sensor bandwidth, due to the time-averaged nature of such free precession measurements. We present an analytic correction dependent on dead-time, and show how this equation can also correct the sensor spectral density. The maximum in-band amplitude loss approaches 29\% as the frequency of interest becomes the Nyquist frequency, making a significant correction for applications such as source localization in magnetoencephalography. These pump and probe atomic magnetometers also are known to have large aliasing of out-of-band signals, and we propose a scheme where the frequency of out-of-band signals can be identified by performing fits with varying dead-time on the raw free-precession sensor data.