Miniature quad-channel spin-exchange relaxation-free magnetometer for magnetoencephalography
Li Jian-Jun1, 2, Du Peng-Cheng1, 2, Fu Ji-Qing3, Wang Xu-Tong1, 4, Zhou Qing4, Wang Ru-Quan1, 2, ‡
       

Plot of the gradient field sensitivities of the sensor. For the channel A–B (blue trace), A–D (red trace), and C–B (yellow trace) gradiometers, the inferred single-channel sensitivity is 4 fT/Hz1/2–6 fT/Hz1/2 between 30 Hz and 100 Hz, and that of channel C–D (purple trace) is 3.5 fT/Hz1/2 over 60 Hz–100 Hz.