What Is a Fluxgate Magnetometer?

A fluxgate magnetometer is a type of scientific instrument used to detect variations in the Earth's magnetic field. Fluxgate magnetometers play an important role in detecting underground or underwater objects. Archaeologists, engineers, geologists and the military all use or have used different types of fluxgate magnetometer.

A fluxgate magnetometer is a vector magnetometer, which means that it measures not only the magnitude but also the direction of the Earth's magnetic field. The device consists of two ferromagnetic cores surrounded by two wire coils. When the magnetometer is active, alternating current passes through one of the coils, known as the "winding coil," creating induced magnetic fields of different intensities and complementary direction in the cores. Changes in the magnetic fields generate an electrical current in the second coil, known as the "sense coil," which can then be measured. Exposure to variations in the earth's magnetic field causes variations in the magnetic fields of the cores, leading to changes in the current in the sense coil.

Victor Vacquier invented the fluxgate magnetometer in the 1930s. Low-flying airplanes carried fluxgate magnetometers during the Second World War. Large items made of ferrous metals, such as submarines, cause localized variations in the Earth's magnetic field, so the magnetometer was able to detect enemy vessels.

Military use of the fluxgate magnetometer continued after the Second World War. Fluxgate magnetometers are highly suited to fieldwork because of their durability and small size. As a result, they became a common tool in the detection of unexploded ordnance such as bombs, artillery shells and land mines.

The military were not the only customers for a light, portable instrument which could detect variations in the Earth's magnetic field. Following the Second World War, and increasingly from the 1960s onward, archaeologists began to make use of fluxgate magnetometers to detect underground features. Ferrous metals were not the only substances archaeologists used magnetometers to search for. Burning locally alters the magnetic field of substances such as stone, earth and pottery, allowing archaeologists to detect deposits of ancient material. The fluxgate magnetometer became a particular favorite with archaeologists not only because of its lightness and durability, but also because of its typically low cost.

The fluxgate magnetometer is also used in physics research. These instruments are mounted on aircraft or spacecraft and used to measure variations in the magnetic field in the atmosphere. Spacecraft-mounted fluxgate magnetometers can measure the magnetic fields of planets other than Earth.