Low temperature SQUID magnetometer systems for geophysical exploration with transient electromagnetics

Abstract

Geophysical exploration is getting more and more difficult—many of the easily explorable ore-bodies have been discovered and are already being exploited. Finding new mines requires new technologies and tools. Transient electromagnetics (TEM) is widely used in mineral exploration, but conventional sensors (especially induction coils) cannot fulfil the needs anymore: deep targets, very conductive targets or targets under conductive overburden are more easily (or sometimes only) detected using SQUIDs. In this paper we will focus on low temperature SQUID magnetometers. As the systems are applied worldwide it is necessary to strengthen them for all conceivable application scenarios. Here, we report on the latest development of these systems which are now routinely used in South Africa, Australia, Finland and Canada. This paper highlights the main features of the system and describes one example from mineral exploration.

Toward ultra high magnetic field sensitivity YBa2Cu3O7−δ nanowire based superconducting quantum interference devices

“…This would allow the realization of nanoSQUIDs able to reach a magnetic field sensitivity in the range of fT= ffiffiffiffiffiffi Hz p , which represents the ultimate goal for various applications. [5][6][7]31 IV. CONCLUSIONS…”

Kinetic inductance magnetometer

“…U ltrasensitive magnetic detection is utilized in a variety of applications, such as magnetoencephalography 1 , magnetocardiography 2 , ultra-low-field NMR 3 and magnetic resonance imaging (ULF NMR and MRI) [4][5][6] , exploration of magnetic minerals 7 and a wide range of other scientific purposes. The most established method is to use superconducting quantum interference devices (SQUIDs) based on low critical temperature superconducting materials 8,9 as the sensor, featuring field sensitivity in the fT Hz À 1/2 regime or below.…”

First evidence of detecting surface nuclear magnetic resonance signals using a compact B‐field sensor

“…Using an LT SQUID sensor which is regularly used in transient electromagnetic surveys [ Chwala et al , ] and provides a magnetic field resolution of about 1.5 fTHz −1/2 , we conducted a field measurement at the LIAG test site in northern Germany to investigate whether SNMR signals can be detected in a routine experimental setup. For this test, we used a Geomagnetic Resonance (GMR) SNMR device of Vista‐Clara [ Walsh , ] with a 50 m diameter circular loop as coincident transmitter and receiver to conduct a traditional SNMR depth sounding.…”

“…As explained earlier in the text, we used a 50 m diameter circular loop that acted as coincident loop transmitter and receiver. A SQUID sensor [ Chwala et al , ] was placed in the center of the loop. Our transmission scheme was to use a 40 ms on‐time pulse across 20 moments with a maximum pulse moment of 10 As over 32 stacks and a dead time of 10 ms.…”

“…To mitigate the above‐mentioned drawbacks of measuring SNMR signals with coincident loops, we propose using point‐like B‐field sensors, such as superconducting quantum interference devices (SQUIDs) [ Chwala et al , ] or Abitibi‐RMIT sensor (ARMIT) [ Macnae , ] coils, that are capable of directly measuring the response field of the subsurface. In this letter, we present the first evidence of detecting a SNMR signal using a point B‐field sensor at a test site in Schillerslage, northern Germany [ Dlugosch et al , ].…”