Electronic high-temperature radio frequency superconducting quantum interference device gradiometers for unshielded environment

Abstract

This article will discuss improved electronically formed gradiometers based on high-temperature radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. For gradiometer balancing, a system of adjustable superconducting plates was developed. This technique was used to build first- and second-order, axial gradiometers with adjustable baselines, which operate at 77 K. Each magnetometer combines a washer rf-SQUID with bulk or a thin-film flux concentrator in flip chip geometry. In an unshielded environment, the magnetic field sensitivity in the white noise region is about 80 fT/√Hz for first-order and 150 fT/√Hz for second-order gradiometer. Common mode rejection could be balanced to better than 104 for uniform background fields and better than 200 for gradient fields.

High-transition-temperature superconducting quantum interference devices

“…More recently, Ockenfuß et al (1997) made a systematic study of thin-film, single-layer flux transformers. The flux transformers were deposited on either 1Љ or 2Љ diameter substrates.…”

Single Sensor High-Temperature Superconducting Axial Gradiometer With Thick Film Pick-Up Loops

“…The noise floor is flat down to low frequencies. The gradient sensitivity is given by (2) where is the flux spectral density, is the baseline and is the effective area of the gradiometer with one pick-up loop cut, as described above. Using the values described earlier we estimate that for this gradiometer at 1 kHz inside shielding.…”

“…Several groups have used multiple Superconducting Quantum Interference Device (SQUID) magnetometers with electronic signal subtraction techniques to form first-or higher-order gradiometers [1], [2]. This places great demands on the electronics in terms of the system linearity and slew rate, although ways to improve this have been implemented [3], [4].…”

HTS SQUID gradiometer using substrate resonators operating in an unshielded environment - A portable MCG system

“…Reported were first and second order axial electronic rf SQUID gradiometers with mechanical balance adjustment [2], [3], and without [4], as well as dc SQUID gradiometers with planar first order gradiometric antennas [5]. However, in contrast to the presently tested concept, these instruments operated with a fixed baseline length and, in most cases, with conventional rather than adaptive balancing [6].…”