Multichannel applications of double relaxation oscillation SQUIDs

Double relaxation oscillation SQUIDs (DROSs) provided high flux-to-voltage transfers of larger than 1 mV Φ 0 −1 and simple flux-locked loop circuits were used for SQUID operation. We constructed two multichannel systems based on DROSs. The first system is a 40-channel planar gradiometer system consisting of integrated first-order pickup coils. average noise level of the 40 channels is 1 fT cm −1 Hz −1/2 at 100 Hz, corresponding to a field noise of 4 fT Hz −1/2 , operating inside a magnetically shielded room. The second one is a 37-channel magnetometer system with 37 integrated magnetometers distributed on a spherical surface and measures field component normal to the head surface. The average noise of the magnetometers is 3 fT Hz −1/2 at 100 Hz. The two systems were applied to measure neuromagnetic fields.