Multiple squid direct signal injection device formed on a single layer substrate

A low-noise directly coupled dc SQUID magnetometer is disclosed. The magnetometer provides for single layer fabrication and is particularly applicable to high-Tc superconductors operating at 77 Kelvin. A pair of dc SQUIDs are connected and biased in series such that the output voltage modulation with applied flux of the dual SQUID magnetometer, is double that of a single SQUID magnetometer. The bias current is applied to one SQUID and removed from the second SQUID of the pair. The magnetometer pick-up coil is directly coupled to the SQUID pair, providing for coherent modulation of the series-connected SQUIDS and a reduction of flux density noise of the device by a factor of 1/ 2ROOT +E,rad 2+EE .