Analysis of Novel Superconducting Magnetometer with Superior Noise and Coupling Properties

摘要

There is considerable interest in the development of extremely sensitive superconducting magnetometers for the detection of changes in magnetic field intensity. The most sensitive detectors developed up to this time are thin film dc SQUID magnetometers. The dc SQUID consists of a superconducting loop interrupted by two Josephson junctions. If the junctions are biased near the critical current by an externally applied dc bias current, the voltage across the junctions becomes a sensitive function of the flux threading the loop. Thus, the dc SQUID acts like a flux to voltage transducer. The resolution of the dc SQUID magnetometer is determined predominately by three factors. First, the Josephson junctions employed in the device must be non-hysteretic. As a result, the thin film tunnel junctions typically used in the device are externally shunted by a normal resistance. The Johnson noise associated with this resistance produces fluctuations in the voltage across the SQUID.