Characterizing atomic magnetic gradiometers for fetal magnetocardiography

Abstract

Atomic magnetometers (AMs) offer many advantages over superconducting quantum interference devices (SQUIDs) due to, among other things, having comparable sensitivity while not requiring cryogenics. One of the major limitations of AMs is the challenge of configuring them as gradiometers. We report the development of a spin-exchange relaxation free (SERF) vector atomic magnetic gradiometer with sensitivity of 3 fT cm −1 Hz −1/2 and common mode rejection ratio (CMRR) > 150 in the band from DC to 100 Hz. We introduce a background suppression figure of merit for characterizing the performance of gradiometers. It allows for optimally setting the measurement baseline, and for quickly assessing the advantage, if any, of performing a measurement in gradiometric mode. As an application, we consider the problem of fetal magnetocardiography (fMCG) detection in the presence of a large background maternal MCG signal.

Detection of biological signals from a live mammalian muscle using an early stage diamond quantum sensor

“…Although it may not be desirable or necessary to minaturise the setup for microscopy in order to maintain mechanical stability and ease of access for users, a portable handheld diamond sensor would allow recording of signals from living whole organisms, in particular for faster signals (kHz bandwidth and above) that cannot be easily detected by competing technology. As discussed in our previous work, feeding multiple diamond sensors from the same central laser via fibre optic coupling would be highly desirable, particularly in terms of spatially resolving the location of signals within tissue and to perform gradiometry to reduce common mode noise 35 . An alternative direction is full miniturisation and integration of the sensor using semiconductor nanofabrication techniques, although as yet this has yet to deliver the necessary sensitivity 36 , 37 .…”

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

“…Magnetometers based on (i) and (ii) can reach detection limits of 0.1-1 pT/√Hz [127,128] without requiring magnetic shielding while magnetic sensors based on (iii) provide a detection level of the order of 10 fT/√Hz, but in most cases, they need to be placed in a magnetically shielded room [129][130][131]. The fact, that these magnetometers do not require strong cooling systems such as SQUIDs and are easy to miniaturize which make them very promising in the field of biomagnetic sensing [132][133][134]. The schematic images of the two main geometries are shown in Figure 8.…”

Active Magnetic-Field Stabilization with Atomic Magnetometer

“…Given that the environmental magnetic-field noise has an inverse-power-law frequency dependence and is higher at lower frequencies, the reduced performance of the passive magnetic shielding in suppressing the low-frequency magnetic-field noise needs to be compensated [27]. An efficient method for enhancing the noise rejection ratio in the low-frequency region is through gradiometric detection, i.e., using several identical magnetometers inside the magnetic shield and subtracting the measurement results of these magnetometers [28] The noise rejection ratio in the low-frequency region can be improved by actively stabilizing the magnetic field [29][30][31]. The basic idea is to measure the magnetic-field noise with a magnetometer, compare the measured result with a reference, and generate an error signal to feedback control the current in a magnetic-field generator (solenoid or Helmholtz coil) and compensate for the magnetic-field noise.…”

“…Given that the environmental magnetic-field noise has an inverse-power-law frequency dependence and is higher at lower frequencies, the reduced performance of the passive magnetic shielding in suppressing the low-frequency magnetic-field noise needs to be compensated [ 27 ]. An efficient method for enhancing the noise rejection ratio in the low-frequency region is through gradiometric detection, i.e., using several identical magnetometers inside the magnetic shield and subtracting the measurement results of these magnetometers [ 28 ]…”