A 64-channel DC-SQUID magnetometer system

A modular 64-channel SQUID magnetometer system has been developed for biomagnetic applications. The square-shaped double washer DC-SQUIDs are fabricated by thin film technology based on the Nb metal process. The signal is detected by a first-order planar gradiometer with counter-wound 10 mm square-shaped coils and a baseline length of 40 mm. The SQUIDs are operated in a flux locked mode. Each channel can be independently replaced without warming up of the dewar. The system is installed in a magnetically shielded room. The noise level for all 64 channels operated simultaneously is about 7 fT//spl radic/(Hz). Biomagnetic measurements have been carried out on the magnetoencephalogram (MEG) and the magnetocardiogram (MCG).<
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