METHOD OF SUPPRESSING CURRENT DISTRIBUTION NOISE IN SUPERCONDUCTION QUANTUM INTERFERENCE DEVICE

摘要

PURPOSE: To suppress current distribution noise by performing weighting operation by a signal detecting device in respective bias states and using the total of individual weighted output voltages as a mean output voltage which is proportional to only a measured quantity. CONSTITUTION: A gradiometer and a coupling coil which form a closed superconducting current loop detects a magnetic field to be measured, which is varied in a DC superconducting quantum interference device 10, which consists of a superconductive loop 11 and two series-connected Josephson junctions 12. Further, a nonsuperconducting DC terminal 13 is provided between the junctions 12 and connected to a controller 14 which is connected to a modulation device 15, and a device operates on a modulating coil 16 so as to impose magnetic flux modulation through an AC current induced in the loop 11 of the device 10 and is connected to a signal detecting device 17 as well through a preamplifier 18 for the detection and combination of the signal from the device 10. Consequently, the current distribution noise can adequately be suppressed.