Berlin 2008 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 12: Symposium: Cryodetectors and SQUID

TT 12.5: Vortrag

Dienstag, 26. Februar 2008, 11:45–12:00, H 0104

SQUID series array current sensor for measuring dc currents — •Jörn Beyer and Dietmar Drung — PTB, Berlin, Germany

Single SQUIDs are detectors of magnetic flux and show a multi-valued voltage-flux characteristics. In precision measurement systems they are used to sense changes in various physical quantities, e.g. magnetic field, electric current or mechanical displacement, which can be transformed into changes in the magnetic flux threading the SQUID loop. A dc-SQUID-based sensor able to detect a dc signal can be formed by a series array of individual dc-SQUIDs (SSA) with different loop sizes [1]. Due to the varying SQUID loop size such a SSA can per se not achieve a flux noise as low as of a same length SSA of identical SQUIDs. Here, we present a new SSA current sensor for measuring dc currents which comprises of identical individual SQUIDs. In this device, the input signal current is coupled tightly but non-uniformly to the individual array elements. This leads to a single-valued overall voltage-flux characteristics and, therefore, allows a dc input signal to be measured. Apart form the non-uniform input signal coupling the individual SQUIDs of the SSA current sensor can be flux-biased evenly, as well. This has a significant practical advantage as flux offsets equal in all the individual SQUIDs of the array can be compensated. Such flux offsets arise for instance due to asymmetric bias current feed into the array elements which is preferential for adjusting the dynamic resistance and therefore the noise performance. We present the design, simulations and experimental results on the dc-current sensor performance.

[1] P.Carelli et.al., Europhys.Lett. 39, 569 (1997)