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-cha nnel system operating in liquid nitrogen has been developed and used t o measure biomagnetic signals emanating from both the heart and the br ain. The magnetic field sensitivity of the integrated SQUID magnetomet er 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 junction s with YBa2Cu3O7-delta as the superconductor and Ag-Au alloy as the no rmal metal allows the measurements to be performed with standard de bi as electronics. (C) 1995 American Institute of Physics.