Inductive Spurious Coupling of a DC-SQUID to Resonant Input Circuit

摘要

The mutual inductance different from zero that exists in dc-SQUID between the feedback/modulation coil and the input coil is reviewed. This spurious coupling causes many effects when the input circuit of the SQUID is a high Q resonant circuit. In particular it affects the Q of the input circuit, decreasing it or making the system unstable. Measurements showing these effects were made on a dc-SQUID coupled to a gravitational radiation detector. A model to explain the spurious effects is presented and a comparison is made with the experimental measurements; the way to overcome unwanted effects modifying the feedback loop is also presented.