Development Of SERF Magnetometer For Human Magnetoencephalography Measurement

Optically pumped atomic magnetometers in the spin exchange relaxation free?SERF?regime play an increasingly important role in weak biological magnetic fields measurements.Compared with alternative Superconducting quantum interfere device?SQUID?magnetometers,SERF magnetometers have comparable sensitivity,and are unnecessary to work under the cryogenic environment.In this paper,we have overcome many difficulties.Since the magnetometer needs to work in a low magnetic field environment,all of our optical lens frames are self-designed to achieve no magnetization.High-frequency current heating prevents noise from heating.The use of thermal insulation cotton achieves a good thermal insulation effect,and does not greatly affect the detected magnetic field strength of the brain due to excessive thickness.Finally,a highly sensitive noncryogenic rubidium magnetometer based on SERF regime is designed and made.The sensitivity of the SERF magnetometer achieved is equal to 6 fT/ ?Hz?^1/2 at 15 Hz.The human magnetoencephalography?MEG?measurements with the SERF magnetometer inside the shielded barrel is demonstrated.In order to verify the performance of the magnetometer,we measured the differences in brain magnetic fields in the cerebral cortex in the blinking-closeing eyes and the brain magnetic field induced by auditory stimulation.For brain magnetic field measurements,it is necessary to measure magnetic fields at multiple locations simultaneously.For this reason,we develop a multi-channel sensor module based on a single large vapor cell,while the auditory induced magnetic fields perpendicular to the four adjacent positions of the scalp are detected.The sensitivity achieved is equal to 10 fT/ ?Hz?^1/2 at 30 Hz.Finally,we optimized our four-channel magnetometer with the longitudinal parametric modulation,the sensitivity of this SERF magnetometer achieved are equal to 5fT/ ?Hz?^1/2 between 10 Hz and 100 Hz in the x-direction,and 20-30fT/ ?Hz?^1/2 between 5 Hz and 100 Hz in the y-direction.Our magnetometer can measure the normal and tangential magnetic fields simultaneously.The dual-axis vector measurement of magnetic field is very important for magnetoencephalography.