BIOMAGNETIC MEASUREMENTS USING LOW-NOISE INTEGRATED SQUID MAGNETOMETERS OPERATING IN LIQUID-NITROGEN

We have fabricated high-T-c SQUID magnetometers with a pickup coil and a multiturn input coil integrated onto the same substrate. A four-channel system operating in liquid nitrogen has been developed and used to measure biomagnetic signals emanating from both the heart and the brain. The magnetic field sensitivity of the integrated SQUID magnetometer reaches 70 fT/root Hz at 1 kHz and 280 fT/root Hz at 1 Hz. The use of superconductor-normal metal-superconductor (SNS) step-edge junctions with YBa2Cu3O7-delta as the superconductor and Ag-Au alloy as the normal metal allows the measurements to be performed with standard de bias electronics. (C) 1995 American Institute of Physics.