Actively shielded, adaptively balanced SQUID gradiometer system for operation aboard moving platforms

Extremely high dynamic range is required if magnetometer SQUIDs are to be operated while in motion in the earth's field. We have developed an HTS SQUID gradiometer system that uses active shielding and an adaptive signal processing algorithm to achieve the necessary dynamic range. An array of f...

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Bibliographic Details
Published in:IEEE transactions on applied superconductivity 2005-06, Vol.15 (2), p.761-764
Main Authors: Keene, M.N., Humphrey, K.P., Horton, T.J.
Format: Article
Language:English
Subjects:
Active shielding
Adaptive signal processing
Applied sciences
Arrays
Coiling
Coils
Dynamic range
Dynamical systems
Earth
Electrical engineering. Electrical power engineering
Error correction
Error detection
Exact sciences and technology
gradiometer
High temperature superconductors
magnetic anomaly detection
Magnetic measurements
Noise level
Shielding
Signal processing algorithms
SQUID
SQUID magnetometers
SQUIDs
Superconducting quantum interference devices
Transformers and inductors
Transistors
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Summary:Extremely high dynamic range is required if magnetometer SQUIDs are to be operated while in motion in the earth's field. We have developed an HTS SQUID gradiometer system that uses active shielding and an adaptive signal processing algorithm to achieve the necessary dynamic range. An array of four thin-film SQUIDs with flux transformers is configured to form two orthogonal magnetometers and a single-axis gradiometer with a baseline of 10 cm. External field changes are cancelled by a three-axis Helmholtz coil set, driven by integral feedback from the SQUIDs, which surrounds the array. A real time adaptive balancing algorithm corrects for gradient offset, electronics scaling errors, sensor misalignments and uniformity errors in the Helmholtz coils. For outside use, light RF shielding is provided by thin layers of Al foil. In laboratory tests, intrinsic noise levels of 20 pT/m//spl radic/Hz (1 Hz) and 0.3 pT/m//spl radic/Hz (white) were measured. In field trials, the Helmholtz coils provided a shielding factor, for uniform fields, of 50-60 dB (0.1-10 Hz) during roll, pitch and yaw rotations of up to /spl plusmn/5/spl deg/. Adaptive balancing reduced gradient noise to the ambient background level of 80 pT/m//spl radic/Hz (1 Hz) and 1 pT/m//spl radic/Hz (white), whilst in motion.
ISSN:1051-8223
1558-2515
DOI:10.1109/TASC.2005.850046