Biplanar nulling coil system for OPM-MEG using printed circuit boards.

Area of Science:

• Biophysics
• Neuroscience
• Sensor Technology

Background:

• Optically pumped magnetometers (OPMs) offer sensitive, non-invasive measurement of human electrophysiological signals like magnetoencephalography (MEG).
• OPMs require near-zero background magnetic fields for accurate, undistorted measurements.
• Conventional biplanar field nulling coils are costly and difficult to manufacture.

Purpose of the Study:

• To design and fabricate affordable, easily manufactured background magnetic field nulling coils for OPM-based MEG.
• To demonstrate the effectiveness of these coils in reducing background magnetic fields.
• To enable OPM-MEG operation in less stringent magnetic shielding conditions.

Main Methods:

• Designed two-layer Printed Circuit Board (PCB) coils using open-source bfieldtools software to null uniform and gradient magnetic fields.
• Developed a software-based method to create continuous current paths across PCB layers.
• Fabricated coils in two halves for easier manufacturing and assembly.

Main Results:

• Achieved field nulling coil efficiency comparable to or higher than previous methods (1.3 - 7.1 nT/mA).
• Reduced the largest background magnetic field component from 21 nT to 2 nT within a 50-cm spherical volume.
• Successfully recorded somatosensory evoked fields (SEFs) using OPMs in a lightly shielded room, yielding results comparable to SQUID-based MEG in a heavily shielded room.

Conclusions:

• Developed a cost-effective and manufacturable solution for background magnetic field nulling coils using PCBs.
• Demonstrated the feasibility of OPM-MEG in less shielded environments, broadening accessibility.
• Disseminated the design and software as an open-source package (opmcoils) to promote OPM-MEG adoption.