Magnetometers

Magnetometers are instruments that measure magnetic fields. They are used to determine the strength and sometimes the direction of magnetic fields in a wide range of scientific, industrial, and navigational applications. Magnetometers can be classified as scalar or vector devices. Scalar magnetometers measure only the magnitude of the magnetic field, while vector magnetometers determine both magnitude and direction.

Measurement principles vary widely. Hall effect sensors detect field-induced voltage changes in semiconductors. Magnetoresistive sensors rely on changes in electrical resistance. Fluxgate magnetometers use nonlinear magnetic cores to sense ambient fields. Optically pumped magnetometers and other atomic magnetometers use interactions between magnetic fields and atomic spins, often with laser light, to measure field strength with high precision. Superconducting quantum interference devices (SQUIDs) detect extremely small magnetic flux changes using superconducting loops and require cryogenic cooling. Each technology offers different advantages in sensitivity, bandwidth, size, power consumption, and operating conditions.

Earth’s magnetic field, typically around 25 to 65 microtesla at the surface, is a common reference for geophysical work. Applications include geophysical surveys and mineral exploration, navigation and attitude sensing for aircraft and spacecraft, space science investigations of planetary magnetospheres, archeological and geophysical studies, and, in medicine, magnetoencephalography (MEG) using sensitive magnetometers to detect brain activity.

Performance characteristics often include sensitivity (in tesla, nanotesla, or femtotesla ranges), noise, dynamic range, and bandwidth. Calibration, temperature stability, and environmental shielding are important for accurate measurements.