Design of Bi-Planar Coil for Acquiring Near-Zero Magnetic Environment

The magnetic source localization of the brain is very sensitive to artifacts caused by residual magnetic fields in space. Therefore, the high-uniformity magnetic coil is very important to acquire near-zero magnetic environment for magnetoencephalography (MEG). In this article, an optimized target field method (TFM) is proposed, in which bat algorithm (BA) is applied. The BA has excellent ability to search for the globally optimal solution, so the higher-uniformity coil can be designed with the same Fourier orders compare with traditional TFM. This novel method is used to design biplanar coil to compensate for residual magnetic field in space for MEG. Through the simulation and experimental result, the coil system designed by optimized TFM can produce uniform field (within ±5% error) over a volume of 11 cm $\times11$ cm $\times11$ cm. This volume is enough to contain a single brain functional region. Automated control of the coils allows reduction of the maximum component of field from 7.93 ± 0.29 to 0.32 ± 0.004 nT. The biplanar coil will suppress the drift field and bring more stable output signal of optical pumping magnetometers (OPMs). The auditory stimulation experiment proves that the biplanar coil system has significant effect on the MEG experiment.