HIGH-SENSITIVITY MAGNETIC-FLUX SENSORS WITH DIRECT VOLTAGE READOUT - DOUBLE RELAXATION OSCILLATION SQUIDS

The experimental sensitivity of Double Relaxation Oscillation SQUIDs ( DROSs) has been compared with theory and with the results obtained by numerical simulations, The experimental sensitivity ranges from 60 to 13h, where h is Planck's constant, for relaxation frequencies from 0.4 up to 10 GHz. For low frequencies the DROS characteristics can be exp lained by thermal noise on the critical currents. For high frequencies , the voltage-flux characteristis and the sensitivity are limited by t he plasma frequency. The cross-over frequency is at 2 GHz, which is ab out 2 % of the plasma frequency of the DROSs.