COMSOL 6.2 - About the Magnetic and Electric Fields Interface Boundary Conditions

About the Magnetic and Electric Fields Interface Boundary Conditions

The Magnetic and Electric Fields interface boundary conditions are applied in a two-step procedure. This is because only some combinations of electric and magnetic boundary conditions are physically relevant whereas others can lead to unphysical models that violate the current conservation law.


	The basic steps for this are to add the magnetic boundary conditions from the Physics toolbar. Then right-click these magnetic boundary condition nodes to add compatible electric boundary conditions as subnodes.

Step 1: Magnetic Boundary Conditions

With no surface currents present the physics interface conditions

need to be fulfilled. Because the physics interface solves for A, the tangential component of the magnetic potential is always continuous, and thus the first condition is automatically fulfilled. The second condition is equivalent to the natural boundary condition and is hence also fulfilled unless surface currents are explicitly introduced.

Step 2: Electric Boundary Conditions

Depending on specific modeling problems, different electric boundary conditions should be used. To include the modeling of the full-wave effect, for instance, in the frequency domain studies, the most general exterior electric boundary condition is the ; that is,

In some other cases where conducting current is more significant, other electric boundary conditions can be used. For example, at exterior boundaries between conducting and nonconducting materials, the general boundary condition is the , expressed as

which is a natural boundary condition.


	A default Ground subnode is also added under the default Magnetic Insulation node. This is to ensure that default boundary conditions are always specified both for the magnetic vector potential and the electric potential. Additional subnodes are available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.

Table 5-3 lists the interior and exterior boundary conditions available with this physics interface.

Table 5-3: Interior and Exterior Electric and Magnetic Boundary Conditions for the Magnetic and Electric Fields Interface.
Node	Interior	Exterior
Magnetic Boundaries
Background Magnetic Flux Density		x
Impedance Boundary Condition		x
Lumped Port	x	x
Magnetic Continuity	x
Magnetic Field		x
Magnetic Insulation	x	x
Magnetic Potential	x	x
Magnetic Shielding	x
Perfect Magnetic Conductor	x	x
Surface Current	x	x
Thin Low Permeability Gap	x
Transition Boundary Condition	x
Coil	x
Electric Boundaries
Contact Impedance	x
Electric Insulation	x	x
Electric Potential	x	x
Electric Shielding	x
Floating Potential	x	x
Ground	x	x
Normal Current Density		x
Periodic Condition		x

Boundary Condition Combinations

Table 5-4 shows the possible combination of magnetic and electric boundary conditions, with an explanation of the physical model represented by the more advanced combinations.

Table 5-4: possible combinations of Electric and Magnetic Boundary Conditions for the Magnetic and Electric Fields Interface.
Magnetic feature	electric feature	physical model
Magnetic Insulation	Electric Insulation
	Electric Potential
	Ground
	Floating Potential
	Terminal
	Normal Current Density
Magnetic Continuity	<none>	<no effect>
	Electric Insulation	Thin nonconducting, nonmagnetic layer, such as an air gap or crack in a metal. It can be used to model internal insulation.
	Contact Impedance	Thin resistive, nonmagnetic layer, such as an oxide layer in a metal.
Magnetic Shielding	<none>	Magnetic (high-μr) layer with same conductive properties as the surrounding medium.
	Electric Shielding	Thin magnetic, highly conductive layer (high-μr, high-σ).
	Electric Insulation	Thin nonconducting magnetic layer.
	Contact Impedance	Thin resistive magnetic layer.
Surface Current	<none>	Externally imposed surface current density.
	Electric Shielding	Thin nonmagnetic, highly conductive layer along which a surface current density flows, that is automatically included in the parent node.
Background Magnetic Flux Density	Electric Insulation
	Electric Potential
	Ground
	Floating Potential
	Terminal
	Normal Current Density