fluxgatemagnetometer

A fluxgate magnetometer is a device used to measure magnetic fields by exploiting the nonlinear magnetic response of a ferromagnetic core driven into saturation. An alternating excitation current in a driving winding saturates the core, and a sensing coil detects the resulting magnetic flux. The presence of an external magnetic field alters the symmetry of the core’s saturation, which changes the amplitude and phase of the detected signal. By demodulating the sensed signal, typically at a harmonic of the excitation frequency, the component of the external field along the excitation axis is obtained. Using multiple axes or separate sensor heads allows reconstruction of a vector magnetic field.

Principle and operation: The core is periodically driven into saturation by an ac excitation, while the external field biases the core’s permeability. The interaction generates harmonics at even orders, and the electrical signal in the pickup coil is proportional to the external field component. Synchronous demodulation or phase-sensitive detection converts this signal into a dc or low-frequency output representing the magnetic field. Calibration relates the output to field strength, and vector measurements are achieved with tri-axial configurations or by rotating sensors.

Construction and performance: Fluxgate sensors commonly use ferrite, nanocrystalline, or amorphous cores. Excitation frequencies range from tens to a few hundred hertz. The systems are designed for stability, low drift, and temperature compensation. They offer good robustness, compact size, and low power consumption, with sensitivity typically in the nanotesla to picotesla per root hertz range for high-performance versions, and adequate dynamic range for geomagnetic and spacecraft applications.

Applications: Fluxgate magnetometers are widely used in geophysics, space science, and navigation. They measure Earth’s magnetic field, monitor magnetic disturbances, support attitude determination on spacecraft, and serve as robust, low-cost field sensors in industrial and research settings.