Resonance damping in tightly coupled d.c. SQUIDs via intra-coil resistors

Intra-coil damping is demonstrated to be an effective method for reducing r esonance structure in well coupled d.c. SQUIDs with large input coils. A re sistance of 1 Omega is placed across each turn of a 137 turn coil coupled t o a planar washer d.c. SQUID. Non-ideal structure in the voltage-flux curve is greatly reduced, extending the range (in current bias) of satisfactory device operation. The resulting flux noise, while higher than the thermal n oise limit, is less than that observed in undamped devices and can be predi cted with a simple model. (C) 2001 Elsevier Science B.V. All rights reserve d.