| 摘要 |
A superconducting magnetic sensor includes a SQUID for interlinking with an external magnetic flux, an A.C. bias circuit for driving the SQUID with an A.C. bias current having a first frequency, a feedback circuit supplied with output voltage pulses from the SQUID for calculating a difference between the total number of positive output voltage pulses and the total number of negative output voltage pulses and for producing a feedback magnetic flux in response thereto such that the external magnetic flux is canceled out by the feedback magnetic flux, and a modulation current source for supplying a modulation current having a frequency substantially smaller than the frequency of the bias current and for producing a modulation magnetic flux in response to the modulation current such that the modulation magnetic flux interlinks with the SQUID.
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