Magnetic field sensors with digital feedback read-out

Magnetic field sensors consisting of a DC superconducting quantum interference device (SQUID) and a close-by superconducting digitizer, both realized in NbN-MgO-NbN technology, are presented. The superconducting circuits have been specifically designed to suppress the influence of external fields on the operation of the sensor and to assure good balancing for gradiometer input coils. It is shown how the different parts of the sensor can be adapted for different modes of operation. The superconducting sensors are operated with digital feedback electronics mounted in the dewar. The operation of digital circuitry in the vicinity of the sensors affects their operation slightly. Most functions, particularly the adjustment and optimization of bias points, can be controlled from a remotely positioned data acquisition system. In view of multisensor applications several precautions have been taken to decouple the data acquisition from the electronics units.<>