fluxgate

Fluxgate magnetometer, or fluxgate, is a type of magnetometer that measures magnetic fields by exploiting a saturable ferromagnetic core driven by an alternating current. The external magnetic field biases the core’s magnetization during each cycle, causing a detectable change in the harmonic content of the core's magnetic flux. A sensing coil detects this perturbation and, after demodulation, yields an output proportional to the field component along the core axis.

Most fluxgate sensors use a high-permeability ferromagnetic material such as permalloy formed into a closed core with a drive coil and a separate sensing coil. The drive current rapidly saturates the core; the external field introduces asymmetry that generates even-harmonic content in the core’s response. Demodulation of this harmonic provides a voltage proportional to the external field. Vector measurements are obtained with multiple cores or by orthogonal coil arrangements.

History and applications: The fluxgate concept emerged in the mid-20th century and became widely used for geophysical surveys, navigation, and space science. Fluxgate magnetometers have flown on numerous spacecraft to map planetary and solar magnetic fields and are found in aircraft, ships, and ground stations for magnetometry.

Advantages and limitations: Fluxgate sensors offer good sensitivity over a wide dynamic range, robustness, and relatively low power consumption, making them practical for compact instruments. They require calibration and temperature compensation to maintain accuracy, and performance can be affected by temperature drift and magnetic noise. Modern implementations often incorporate digital signal processing to improve stability and linearity.