Improved high-T_csuperconducting quantum interference filters for sensitive magnetometry

Abstract

Superconducting quantum interference filters (SQIFs) are arrays of superconducting loops, with Josephson junctions, of diverse loop sizes. The dependence of the SQIF voltage on external magnetic fields is non-periodic and shows only one unique peak at zero field. We present several kinds of SQIFs-serial arrays, parallel arrays and various combinations of both-which are all realized with high-T c superconductors. Compared to a single SQUID all SQIF types show improved magnetic field sensitivity and noise-limited field resolution. In order to realize really sensitive magnetometers the SQIFs were coupled to pickup coils. Consequently, the sensitivity and noise of the SQIF-based magnetometers are comparable with that of their SQUID-based counterparts. For a flip-chip configuration using a serial-parallel SQIF and a superconducting flux transformer, a noise-limited field resolution of 70 fT Hz −1/2 was achieved. This is only twice the value of that using a normal SQUID. Further reduction should be possible by a better adaptation of the complete design to the SQIF options.

Superconducting Quantum Interference Filters as Absolute Magnetic Field Sensors

“…Additional noise properties of similar SQIFs in active microcoolers are presented elsewhere [16]. Recently, higher magnetic field resolution has been achieved in SQIFs with a specially sensitive pick-up loop design [18].…”

High-Tc superconducting quantum interference filters (SQIFs) made by ion irradiation

“…Values found in the literature are generally lower [3,9,10]. However, the comparison is limited since the number of SQUIDs involved is more than an order of magnitude different, and the total impedance of the system is very different as well.…”

“…For high-frequency applications, very interesting results have been obtained such as [8][9][10][11][12][13][14][15] GHz antennas in the near field [8], and RF amplifiers in the 12 GHz range [5]. These performances have been obtained using low T c materials,…”

Examples of superconducting technology application: Sensing and interfacing

“…First experiments using a standard array of SQUID loops are performed without any pickup loop coupled to the bare SQIF [18,19]. In general, the serial SQIFs work properly and show the expected increase in peak height and a reduction of the magnetic field noise with an increase in the number N of SQUID loops.…”