Free Space
For inductive and capacitive (sometimes resistive) analysis, it is quite common for the fields to extend into the environment of the device in question. It is therefore important not only to model the device itself, but also its (close) surroundings. Typically, this is done by adding a box or sphere around the device’s geometry.
The default Free Space node is used to specify the physical conditions in close proximity to the device — typically in air or vacuum. It adds the Ampère’s law and current conservation governing equations with a limited set of material models: the permeability μr and permittivity εr are assumed to be one, and the conductivity is taken from the Stabilization conductivity.
The Free Space feature provides a canvas on top of which other features can be added to locally specify material properties and excitation forms.
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).
Stabilization
Stabilization Conductivity
The Stabilization conductivity allows for four options:
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From material; use the conductivity specified by the material.
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Automatic (default); sets a conductivity σstab = 1 S/m for stationary and time dependent studies, and σstab = 0 otherwise. This is done in order to avoid getting a singular problem, which can happen when the conductivity is zero. For more information, see Theory for the Magnetic and Electric Fields Interface.
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Off; disable the stabilization conductivity altogether: σstab = 0. This models a perfect vacuum and is a good approximation for air.
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User defined; specify a suitable stabilization conductivity directly.