Title :
A coupled DC SQUID with low 1/f noise
Author :
Seppa, H. ; Kiviranta, M. ; Satrapinski, A. ; Gronberg, L. ; Salmi, J. ; Suni, I.
Author_Institution :
VTT, Tech. Res. Centre of Finland, Espoo, Finland
fDate :
3/1/1993 12:00:00 AM
Abstract :
A low-noise coupled DC superconducting quantum interference device (SQUID) especially optimized for low frequency is discussed. Using large Josephson junctions and a low loop inductance the contribution of the critical current fluctuation to 1/f noise can be minimized. To minimize the inductance the Josephson junctions are placed in the center of the washer close to the SQUID loop. A scaled-up copper model of the SQUID and the signal coil is used to analyze the impedance of the SQUID loop affected by the signal coil. An equivalent circuit model describing the effective inductance of the SQUID loop as a function of the frequency is used to design appropriate damping of the resonances. The DC SQUID characteristics are smooth and the noise performance of the SQUID does not markedly suffer from resonances. The contribution of the 1/f noise at 1 Hz is found to be about 5*10/sup -7/ Phi /sub 0// square root Hz.<>
Keywords :
SQUIDs; critical currents; electron device noise; equivalent circuits; inductance; random noise; coupled DC SQUID; critical current fluctuation; equivalent circuit model; impedance; inductance; large Josephson junctions; low 1/f noise; low loop inductance; microwave resonance damping; noise performance; scaled-up copper model; signal coil; superconducting quantum interference device; Coils; Critical current; Frequency; Inductance; Interference; Josephson junctions; Resonance; SQUIDs; Superconducting device noise; Superconducting devices;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
