A 37-CHANNEL DC-SQUID MAGNETOMETER SYSTEM

A 37-channel DC SQUID magnetometer system has been built for biomagnet ic studies. The SQUID loop of each magnetometer serves as the active s ensing element, thereby eliminating the need for flux coupling circuit s. The magnetometers are located approximately 3 cm above the outer de war bottom. The SQUIDs are directly coupled to highly simplified read- out electronics using only five wires per channel; no helium temperatu re impedance matching circuits are required. Each channel can be indep endently inserted into or removed from the dewar. Using a novel electr onic noise reduction technique the system white and 1 Hz flux density noise values are typically 5 and 10 fT Hz-1/2, respectively, including the noise contribution of the in-house fabricated dewar and the magne tically shielded room. The two parts of the data-processing system all ow independent handling of the acquisition and analysing task. Two exa mple measurements demonstrate the advantage of the electronic noise re duction method.