Evaluation of Self-Field Effects in Magnetometers Based on Meander-Shaped Arrays of Josephson Junctions or SQUIDs Connected in Series.

Denis Crété,Juan Trastoy,Christian Ulysse,Bruno Marcilhac,Salvatore Mesoraca,Julien Kermorvant,Yves Lemaître

doi:10.3390/mi12121588

Abstract

Arrays of superconducting quantum interference devices (SQUIDs) are highly sensitive magnetometers that can operate without a flux-locked loop, as opposed to single SQUID magnetometers. They have no source of ambiguity and benefit from a larger bandwidth. They can be used to measure absolute magnetic fields with a dynamic range scaling as the number of SQUIDs they contain. A very common arrangement for a series array of SQUIDs is with meanders as it uses the substrate area efficiently. As for most layouts with long arrays, this layout breaks the symmetry required for the elimination of adverse self-field effects. We investigate the scaling behavior of series arrays of SQUIDs, taking into account the self-field generated by the bias current flowing along the meander. We propose a design for the partial compensation of this self-field. In addition, we provide a comparison with the case of series arrays of long Josephson junctions, using the Fraunhofer pattern for applications in magnetometry. We find that compensation is required for arrays of the larger size and that, depending on the technology, arrays of long Josephson junctions may have better performance than arrays of SQUIDs.

Highlights

Superconductive quantum interference devices (SQUIDs) have excellent performance in magnetometry, offering simultaneously very high transfer factors, very low noise and very large bandwidth [1]
A semi-circular track connects the ends of consecutive segments in the series array
We have investigated the scaling of arrays of Josephson and/or SQUIDs connected in series and its limitations

Summary

Introduction

Superconductive quantum interference devices (SQUIDs) have excellent performance in magnetometry, offering simultaneously very high transfer factors, very low noise and very large bandwidth [1]. Using them in a flux-locked loop [2] adds the advantage of a large dynamic range. SQUIDs [8–12], depending on the probing loop size [13,14]. These techniques can be used for applications that do not require bandwidth in excess of a few MHz (or 150 MHz when only the flux-locked loop technique is used). These limitations are due either to the size of the feedback loop or to the speed of the modulation electronics. In the case of loop unlocking, when the locking point is recovered, it is difficult—if not impossible—to

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