SQUIDs for magnetic and electromagnetic methods in mineral exploration

Abstract

Research on quantum sensors for the detection of magnetic fields (quantum magnetometers) is one of the fast-moving areas of Quantum Technologies. Since there exist expectations about their use in geophysics, this work will provide a brief overview on the various developing quantum technologies and their individual state of the art for implementing quantum magnetometers. As one example, the developments on superconducting quantum interference devices, so-called SQUIDs as a specific implementation of a quantum magnetometer, are presented. In the course of this, SQUID instrument implementations and associated demonstrations and case studies will be presented. An airborne vector magnetometer with ultra-low noise ($$<10 \mathrm{fT}/\sqrt{\mathrm{Hz}}$$ < 10 fT / Hz ) and high dynamic range of $$>32 \mathrm{bit}$$ > 32 bit will be introduced which has the prospect to be applied for the magnetic method in parallel with electromagnetic methods such as passive audio-frequency magnetics or semi-airborne methods using active transmitters such as elongated grounded dipole sources. The according signals are separated in the frequency domain. A second implementation is an airborne full tensor gradiometer instrument will be discussed which has shown already a number of successful case studies and which turned into commercial operation in the past years. Besides the airborne instrument, a very successful implementation of quantum magnetometers is the SQUID-based receiver for the ground-based transient electromagnetic method. Today it is a mature technology which has been in commercial use for more than a decade and has led to a number of discoveries of conductive ore bodies. One case study will be presented which demonstrates the performance of this instrument. Finally, future prospects of using quantum magnetometers, including SQUIDs and new optically pumped magnetometers, in geophysical exploration will be discussed. Particular applications for both sensor types will be introduced.

Calibration method for planar SQUID gradiometers based on the magnetic gradient tensor components

“…When the z-axis Maxwell coils are driven by the linear power amplifier and the AC signal source, we change the height of the planar SQUID gradiometers along the z-axis of the dewar and measure their outputs at discrete measurement points to evaluate the effect of gradiometer position on calibration errors. The tesla/volt calibration factors of the gradiometers can be obtained from equation (5). To facilitate the evaluation of changes, figure 7(a) shows the ratio of the calibration factors of the planar SQUID gradiometer G1 to their averages with different positions.…”

“…inversion and interpretation [3]. Superconducting quantum interference devices (SQUIDs), which are intrinsically fluxto-voltage transducers, are the most sensitive detectors of magnetic flux and known to be practical [4] and the most promising technology for building hardware gradiometers for MGTs [1,5]. There are two common types of hardware gradiometers, axial gradiometers and planar gradiometers.…”

Gradiometry Processing Techniques for Large-Scale of Aeromagnetic Data for Structural and Mining Implications: The Case Study of Bou Azzer Inlier, Central Anti-Atlas, Morocco

“…These devices have been demonstrated to be successful for observing geomagnetic phenomena. IPHT Jena has successfully created and tested full tensor magnetic gradiometer systems based on LTSQUIDs (low-temperature superconducting quantum interference devices) for various targets [33,34].…”

Determinants of Maximum Magnetic Anomaly Detection Distance

“…In seeking higher sensitivity, optically pumped magnetometers are adopted to give pT/ -level equivalent magnetic noise spectrum density, which was tested to be effective in marine UXO detection and identification within a detection distance range of less than 20 m [ 9 , 16 , 17 ]. Thanks to the simultaneous advantages of high sensitivity and a low electric noise floor, SQUID pioneered an exceptionally low equivalent magnetic noise spectrum density of less than 10 fT/ , ultimately offering pT-level measurement resolution to give a detection distance of 33 m for a UXO with a typical size of 2.1 m [ 18 ]. However, applications of optically pumped magnetometers and SQUID are limited because of their bulk size, massive loads and complex electronic accessories [ 19 ].…”