Magnetometers are scientific instruments used to measure magnetic fields. They are often used in physics and engineering laboratories to measure the strength and direction of magnetic fields, especially those produced by electromagnets. Magnetometers can also be used to detect and map natural sources of magnetism such as the Earth’s magnetic field.
The first magnetometer was built in 1832 by Michael Faraday, who is also credited with discovering electromagnetic induction. Faraday’s magnetometer consisted of a coil of wire that was rotated in a magnetic field. The current flowing through the coil could be measured, and from this the strength of the magnetic field could be calculated.
Magnetometers usually consist of three basic parts: a sensor, a readout device, and some means of applying a known magnetic field to the sensor (called “bias”). The sensor is typically a coil of wire or an array of sensors that produces a voltage when exposed to a magnetic field; this voltage is proportional to the strength of the field. The readout device converts the sensor output into some form that can be read by humans or other devices; for example, it might display the output on an analog meter or digital readout device, or it might store it in computer memory for later analysis. The bias source applies a known reference field to calibrate the instrument; without this calibration step, absolute measurements would not be possible.
There are many different types of magnetometers available today; they vary in size, sensitivity, accuracy, price, and so forth. Some common types include fluxgate magnetometers (which use electronic sensors), searchcoils (which use moving coils), SQUIDs (superconducting quantum interference devices), proton precession magnets (in which hydrogen nuclei spin in response to applied fields), and optically pumped atoms (in which laser light alters atomic spin states). Each type has advantages and disadvantages depending on its intended application; for example, fluxgate magnetometers are very rugged but relatively insensitive compared to SQUIDs; proton precession magnets are extremely sensitive but require cryogenic cooling (-269°C)to function properly.