The Free Space node is the default domain feature in the Magnetic Machinery, Rotating, Time Periodic interface. It adds the Ampère’s law in free space and assumes that all domains have a uniform relative magnetic permeability of one.

Free Space assumes vacuum conditions, hence it does not require any material, but also a material with vacuum properties will be accepted. If the feature is applied on a selection that spans over materials with properties that are found to be inconsistent with that of vacuum, these will be ignored, and a warning is added to the solver. This can be fixed by adding appropriate physics features for the ignored materials. Otherwise, it is possible to disable the consistency check of materials by means of clearing the Check applicability of features in study checkbox in the Check consistency section that is available at the physics level (notice that the section is visible only after clicking the Show More Options button () and selecting Advanced Physics Options in the Show More Options dialog).