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It has been found that when superconducting quantum interference device magnetometers operate in a geomagnetic field environment, its output will occasionally show small momentary jumps with the change of the external magnetic field, which seriously affects the measurement accuracy of the geomagnetic field and needs to be eliminated. A magnetic flux jump model called the parasitic superconducting ring model was built to explain the causes of these small jumps, and Helmholtz coils were set up to study the jump and verify this model in the laboratory. The experimental results showed that the position and amplitude of the jumps were consistent with the model. It is believed that this model can guide the design of superconducting chips in geophysical applications. [ABSTRACT FROM AUTHOR]

Transient electromagnetic method (TEM) is an effective way for mineral resource prospecting if an induction coil is used as the traditional sensor. Superconducting quantum interference device (SQUID) obtains excellent sensitivity at low frequency as compared to coil. Thus, the exploration depth and the accuracy of TEM can be greatly improved. However, an ultrahigh slew rate (>10 mT/s) is needed for transient primary field recording, which is a great challenge for a single high-sensitivity SQUID receiver. In this paper, two SQUIDs with different sensitivities (1.5 nT/Φ0 and 99 nT/Φ0) are employed to record the whole TEM decaying signal. The high-sensitivity SQUID (1.5 nT/Φ0) is in reset status when transmitting and is locked after tens of microseconds after transmitting has been cut off. The low-sensitivity SQUID (99 nT/Φ0) remains locked during the whole procedure with high slew rate (∼198 mT/s) to record the fast-switching transmitting field. The two channel SQUID outputs are combined together to form a complete decaying curve. A field test was carried out. The decaying curve with a noise level of 100 fT@DC-25 kHz and a fast-switching field of ∼630 nT cutting off in tens of microseconds (slew rate up to ∼56 mT/s) was recorded after stacking. This dual-channel SQUID-based TEM system obtains high stability, which is useful for small transmitting loop (<50 m) configuration. [ABSTRACT FROM AUTHOR]

A superconducting quantum interference device (SQUID) planar gradiometer is an extremely sensitive sensor for magnetic gradient measurements. It has been shown to have potential applications for aeromagnetic detection. The major challenge when operating an aeromagnetic SQUID system in actual environment is the motion noise, including the inherent response resulting from gradiometer imbalance and from magnetic interferences. Three orthogonal reference magnetometers are usually adopted to improve the gradiometer balance. However, magnetic interference coming from the system itself also needs to be compensated. In this article, a mathematical model of the motion noise picked up by the gradiometer is derived from the traditional magnetic total field compensation method. Based on the model, the signals from the triaxial magnetometer can also be used to compensate the eddy current contribution to the magnetic interference. To verify the compensation method, a SQUID planar gradiometer system was set up and used for flight trials. The gradient field noise and imbalance of our homemade gradiometer were measured to be 100 fT/m/rt(Hz) and 2E-4 in the lab. In flight, the motion-induced peak-to-peak output of the gradiometer was reduced from 170 to about 0.1 nT/m, so that a magnetic anomaly signal of about 2 nT/m from a cargo ship was clearly recognized. [ABSTRACT FROM AUTHOR]