Abstract
The characteristics of the low T c dc superconducting quantum interference devices (SQUIDs) having a large inductance of 1 nH were investigated. The degradation of the modulation voltage due to the large inductance parameter β L was recovered by damping the SQUID inductance with a resistor having twice the junction resistance. The modulation voltage of 20 µ V was close to the value given by the computer simulation. The value of the measured flux noise, using a dc bias flux-locked-loop with a cooled tank circuit, of 21 µΦ0/√ Hz was about 8 times larger than the theoretical value. The flux noise at the white region increased to 39 µΦ0/√ Hz after removing the tank circuit, but because of the improved flux transfer efficiency from the input coil to the SQUID a white field noise of about 10 fT/√ Hz was obtained using a second order axial gradiometer. A clear auditory evoked field was observed using the large β L SQUID magnetometer which was directly coupled to the amplifier.
Published Version
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