SQUIDs and their applications

This article is a new edition of the text written by Daniel Bloyet and Chantal Gunther.

SQUIDs (Superconducting Quantum Interference Devices) are extremely sensitive superconducting magnetic flux detectors with a wide range of applications: mainly low-current or low-voltage measurements, thermometry, biomagnetism, magnetic property measurements and non-destructive testing.

These are devices whose measuring head (the SQUID itself) operates at low temperature, in most cases at 4.2 K (the boiling temperature of liquid helium at atmospheric pressure) or up to 90 K thanks to the new high-temperature superconducting materials discovered in 1986.

Their operating principle is based on two phenomena: the quantization of magnetic flux through a superconducting loop, and the Josephson effect. Excellent descriptions of SQUID operating principles and applications can be found in the bibliographic references. The continuous SQUID is currently the most widely developed, whether based on low- or high-temperature superconductors; a simplified presentation is given here.