Editing Magnetometer (section)

====SQUID magnetometer====
{{Main|SQUID}}
[[SQUID]]s, or superconducting quantum interference devices, measure extremely small changes in magnetic fields. They are very sensitive vector magnetometers, with noise levels as low as 3&nbsp;fT&nbsp;Hz<sup>−½</sup> in commercial instruments and 0.4&nbsp;fT&nbsp;Hz<sup>−½</sup> in experimental devices. Many liquid-helium-cooled commercial SQUIDs achieve a flat noise spectrum from near DC (less than 1&nbsp;Hz) to tens of kilohertz, making such devices ideal for time-domain biomagnetic signal measurements. SERF atomic magnetometers demonstrated in laboratories so far reach competitive noise floor but in relatively small frequency ranges.

SQUID magnetometers require cooling with liquid [[helium]] ({{Val|4.2|ul=K}}) or [[liquid nitrogen]] ({{Val|77|u=K}}) to operate, hence the packaging requirements to use them are rather stringent both from a thermal-mechanical as well as magnetic standpoint. SQUID magnetometers are most commonly used to measure the magnetic fields produced by laboratory samples, also for brain or heart activity ([[magnetoencephalography]] and [[magnetocardiography]], respectively). Geophysical surveys use SQUIDs from time to time, but the logistics of cooling the SQUID are much more complicated than other magnetometers that operate at room temperature.