A Low-Noise Seven-Channel DC SQUID Magnetometer for Brain Research

The design, construction, and performance of a high-sensitivity DC SQUID magnetometer, covering a circular area of 93 mm diameter, is described. The device, now used routinely in our brain research, comprises seven asymmetric first-order gradiometers, located on a spherical surface of 125 mm radius and with the symmetry axis tilted 30° in respect to the vertical. The overall field sensitivity of the system, measured inside our magnetically shielded room, is 5 - 6 fT/√Hz, mainly caused by thermal noise in the radiation shields of the dewar. © 1987 The Japan Society of Applied Physics.