A conformal array of microfabricated optically-pumped first-order gradiometers for magnetoencephalography
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RESEARCH
Open Access
A conformal array of microfabricated optically-pumped first-order gradiometers for magnetoencephalography N.V. Nardelli1 , A.R. Perry1 , S.P. Krzyzewski1 and S.A. Knappe1,2* *
Correspondence: [email protected] 1 University of Colorado Boulder, Boulder, CO 80309, USA 2 FieldLine Inc., Boulder, CO 80301, USA
Abstract An array of 21 first-order gradiometers based on zero-field optically-pumped magnetometers is demonstrated for use in magnetoencephalography. Sensors are oriented radially with respect to the head and housed in a helmet with moveable holders which conform to the shape of a scalp. Our axial gradiometers have a baseline of 2 cm and reject laser and vibrational noise as well as common-mode environmental magnetic noise. The median sensitivity of the array is 15.4 fT/Hz1/2 , measured in a human-sized magnetic shield. All magnetometers are operated independently with negative feedback to maintain atoms at zero magnetic field. This yields higher signal linearity and operating range than open-loop operation and a measurement system that is less sensitive to systematic and ambient magnetic fields. All of the system electronics and lasers are compacted into one equipment rack which offers a favorable outlook for use in clinical settings. Keywords: Magnetometer; Atomic; Laser sensors; Quantum sensors; Optical instruments; Micro-optical devices; Spin-exchange relaxation-free (SERF); Magnetoencephalography (MEG); Optically-pumped magnetometer (OPM)
1 Introduction Measuring DC magnetic fields with high precision is important for biomedical imaging applications such as magnetoencephalography (MEG) [1]. Neuronal signals inside the brain create small magnetic fields that penetrate the skull largely undisturbed and these fields can be detected by an array of sensitive magnetometers placed centimeters to millimeters from the surface of the scalp. Reconstruction algorithms can use the combined magnetometer data to create 3D current density maps with high spatial and timing resolution [2, 3]. Superconducting Quantum Interference Devices (SQUIDs) have become the predominant tool for MEG applications [4, 5], where roughly 300 low-temperature SQUID sensors are placed into a head-shaped liquid helium dewar. Over the last 10 years, opticallypumped magnetometers (OPMs), relying on alkali atoms in vapor cells, have emerged as one possible alternative. The non-cryogenic nature is one attractive feature of OPMs, which not only eliminates the need for frequent replenishing of helium, but also allows for © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a
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