Technology explainer
How SQUID Magnetometers Measure Extremely Weak Magnetic Fields
A practical guide to superconducting loops, Josephson junctions, magnetic flux and the cryogenic systems behind SQUID magnetometry.
A superconducting quantum interference device, or SQUID, converts tiny changes in magnetic flux into a measurable electrical signal. Its sensitivity comes from a superconducting loop interrupted by Josephson junctions, where current follows quantum phase relationships.
From field to signal
Magnetic flux through the loop changes the phase of the superconducting current. The paths interfere, producing a periodic voltage or current response. Electronic readout circuits track that response and infer the field change.
Why arrays are used
Combining many SQUID cells can increase output and bandwidth. Designers must also resolve the periodic ambiguity, because the same response may recur at multiple field values. Array geometry and signal processing are therefore as important as raw sensitivity.
The engineering cost
Most SQUIDs require cryogenic cooling, shielding and low-noise electronics. Those requirements enable exceptional measurements but make complete systems larger and more expensive than the sensor chip alone.
Applications
SQUIDs read weak biomagnetic signals, characterize materials, support scientific detectors and measure electromagnetic signals in research instruments. Performance in one laboratory circuit does not automatically transfer to a clinical or field system.
First appeared in
A Simpler SQUID Array Finds Magnetic Zero Without Sacrificing Its Design
