SQUID

A SQUID (superconducting quantum interference device) is a very sensitive magnetometer used to measure extremely weak magnetic fields, based on superconducting loops containing Josephson junctions.

SQUIDs are sensitive enough to measure fields as low as 5×10⁻¹⁸ T with a few days of averaged measurements.^[1] Their noise levels are as low as 3 fT·Hz^−1⁄2.^[2] For comparison, a typical refrigerator magnet produces 0.01 tesla (10⁻² T), and some processes in animals produce very small magnetic fields between 10⁻⁹ T and 10⁻⁶ T. SERF atomic magnetometers, invented in the early 2000s are potentially more sensitive and do not require cryogenic refrigeration but are orders of magnitude larger in size (~1 cm³) and must be operated in a near-zero magnetic field.

^ Ran, Shannon K’doah (2004). Gravity Probe B: Exploring Einstein's Universe with Gyroscopes (PDF). NASA. p. 26. Archived (PDF) from the original on 16 May 2008.
^ D. Drung; C. Assmann; J. Beyer; A. Kirste; M. Peters; F. Ruede & Th. Schurig (2007). "Highly sensitive and easy-to-use SQUID sensors" (PDF). IEEE Transactions on Applied Superconductivity. 17 (2): 699–704. Bibcode:2007ITAS...17..699D. doi:10.1109/TASC.2007.897403. S2CID 19682964. Archived from the original (PDF) on 19 July 2011.

[Ran04-1] Ran, Shannon K’doah (2004). Gravity Probe B: Exploring Einstein's Universe with Gyroscopes (PDF). NASA. p. 26. Archived (PDF) from the original on 16 May 2008.

[2] D. Drung; C. Assmann; J. Beyer; A. Kirste; M. Peters; F. Ruede & Th. Schurig (2007). "Highly sensitive and easy-to-use SQUID sensors" (PDF). IEEE Transactions on Applied Superconductivity. 17 (2): 699–704. Bibcode:2007ITAS...17..699D. doi:10.1109/TASC.2007.897403. S2CID 19682964. Archived from the original (PDF) on 19 July 2011.

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