Observing the Steady-State Visual Evoked Potentials with a Compact Quad-Channel Spin Exchange Relaxation-Free Magnetometer

We observed the steady-state visually evoked potential（SSVEP） from a healthy subject using a compact quad-channel potassium spin exchange relaxation-free（SERF） optically pumped magnetometer（OPM）. To this end, 30 s of data were collected, and SSVEP-related magnetic responses with signal intensity ranging from 150 fT to 300 f T were observed for all four channels. The corresponding signal to noise ratio（SNR） was in the range of 3.5–5.5. We then used different channels to operate the sensor as a gradiometer. In the specific case of detecting SSVEP, we noticed that the short channel separation distance led to a strongly diminished gradiometer signal. Although not optimal for the case of SSVEP detection, this set-up can prove to be highly useful for other magnetoencephalography（MEG） paradigms that require good noise cancellation.Considering its compactness, low cost, and good performance, the K-SERF sensor has great potential for biomagnetic field measurements and brain-computer interfaces（BCI）.