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Apparatus for reducing low frequency noise in dc biased SQUIDS

  • US 4,389,612 A
  • Filed: 06/17/1980
  • Issued: 06/21/1983
  • Est. Priority Date: 06/17/1980
  • Status: Expired due to Term
First Claim
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1. A low noise superconducting circuit for measuring magnetic flux comprising a superconducting device including a pair of Josephson junctions and superconductors connecting the junctions in a closed loop, means applying a bias current through the two junctions in parallel, means reversing the bias current direction through the junction periodically at a first frequency, means for generating magnetic flux linking the closed loop, means modulating said flux at a second frequency which is different from said first frequency, demodulating means responsive to reference signals at said first and second frequencies, and means coupling the voltage across said junctions to said demodulating means, the demodulated output providing an output signal whose amplitude is determined by the level of magnetic flux linking the loop.

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