On-chip self-shielded magnetic-field coil for integrated atomic magnetometers

Optically pumped magnetometers (OPMs) are widely applied in emerging biomagnetic imaging systems, namely magnetoencephalography (MEG) and magnetocardiography (MCG). However, devices of this kind are limited by stray fields generated from magnetic-field coils and interference with adjacent magnetometers, which make further improvement of spatial resolution challenging. In this work, we propose a biplanar axial self-shielded coil design, which differs from conventional multi-plane self-shielded configurations and provides a uniform internal magnetic field with rapid external field decay. The design is based on a hybrid square–circular geometry, with the external field decay evaluated using multipole expansion of the magnetic vector potential. Results demonstrate that the relative inhomogeneity error decreases from 10.4% to 4.2% and decreases the distance required to achieve 1% external field decay from 22.1 mm to 11 mm in x-direction and from 29.5 mm to 18.5 mm in z-direction. The coil is fabricated on a silica wafer using a CMOS-compatible microfabrication process, demonstrating a viable path toward the chip-scale integration of atomic magnetometers.