In electromagnetism, permeability is the measure of magnetization that a material obtains in response to an applied magnetic field.
Even though an RVmagnetics MicroWire sensor is a magnetized element - the permeability is impressive ~ 1, like in a vacuum. This surely enables the sensor to operate in heavily magnetized environments, to provide measurements on the magnetic field, and at the same time to not have biassed measurements from the effects of the heavy magnetic environment.