Magnetometer

A magnetometer measures the strength or direction of a magnetic field. Instruments range from simple compasses to sensitive devices used in laboratories, surveys, and spacecraft.

Hall effect: The production of a voltage across a current-carrying conductor or semiconductor in a magnetic field. Hall-effect sensors infer magnetic-field strength from a voltage generated inside the sensing material.
Magnetic anomaly detection: The detection of localized deviations from an expected magnetic field. Surveys use magnetometers to locate buried objects and map variations in subsurface geology.
Magnetic field: A physical field produced by magnets, electric currents, and changing electric fields that acts on magnetic materials and moving charges. A magnetometer measures this field’s magnitude, direction, or both.
Magnetic compass: A navigation instrument whose magnetized needle aligns approximately with Earth’s horizontal magnetic field. A compass indicates direction, while many magnetometers quantify field strength as well.
Lodestone: A naturally magnetized piece of the mineral magnetite. Lodestones supplied the magnetic needles used in early directional instruments.
Fluxgate magnetometer: A magnetic-field sensor that uses a driven ferromagnetic core to detect field strength and direction. Fluxgates measure vector fields by tracking how an external field changes the core’s magnetic response.
Magnetoencephalography: A method for mapping brain activity by measuring magnetic fields produced by neural currents. Sensitive magnetometers capture the tiny fields generated by active brain tissue.
Magnetic flux density: A vector quantity describing magnetic field strength, measured in teslas. Many instruments report flux density, the quantity commonly denoted by B.
Gaussmeter: An instrument for measuring magnetic flux density, often using a Hall-effect probe. Gaussmeters are commonly optimized for measuring field strength near magnets and equipment.
Compass: A navigation instrument that indicates direction, usually by aligning a magnetized needle with Earth’s field. The compass is the simplest historically widespread magnetic-field instrument.

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