Magnetic Flux
Magnetic flux measurements define the point where a core material can no longer support additional field lines. Magnetic saturation happens because all the internal magnetic domains have aligned with the applied field. This state is temporary and reverses once the external field is removed or reduced.
Flux Density
Once a material reaches this state, any further increase in the excitation current results in only a small increase in flux. For an inductive sensor, magnetic saturation leads to a sharp drop in inductance and a loss of signal linearity. The core material of the coil determines the point at which this occurs.
Soft iron and silicon steel saturate at different levels of field strength.
Sensor Performance
Operating near the limit causes distortion in the output waveform and generates heat due to energy losses. Designers must ensure that the magnetic saturation level is well above the maximum expected operating current. This involves choosing a core size and material that can handle the peak flux without entering the non linear region.
Testing is performed by measuring the permeability as a function of the drive level.
Core Selection
Ferrites are often chosen for high frequency applications because they have a high electrical resistance but a lower saturation point than metals. The magnetic saturation threshold is the primary constraint when downsizing transformers or inductors.
