The Magnetic Fields, No Currents, Boundary Elements Interface

The interface (

), found under the branch when adding a physics interface, is used to compute magnetostatic fields from permanent magnets and other current free magnetic sources. It can also be coupled to The Magnetic Fields, No Currents Interface or The Magnetic Fields Interface to account for outer, current free regions as an alternative to using Infinite Elements. The formulation is stationary. The physics interface solves Gauss’ Law for the magnetic field using the scalar magnetic potential as the dependent variable.


	For a discussion about the boundary element method, see Theory for the Boundary Elements PDE in the COMSOL Multiphysics Reference Manual.

When this physics interface is added, these default nodes are also added to the — , (on exterior boundaries) and . Then, from the toolbar, add other nodes that implement, for example, magnetic scalar potential and magnetic flux density conditions. You can also right-click to select physics features from the context menu.


	If both The Magnetic Fields, No Currents Interface and The Magnetic Fields, No Currents, Boundary Elements Interface are available, the Magnetic Scalar-Scalar Potential Coupling node is available from the Multiphysics menu in the Physics toolbar or by right-clicking the Multiphysics Couplings node in Model Builder.


	If both The Magnetic Fields Interface and The Magnetic Fields, No Currents, Boundary Elements Interface are available, the Magnetic Vector-Scalar Potential Coupling node is available from the Multiphysics menu in the Physics toolbar or by right-clicking the Multiphysics Couplings node in Model Builder.

Physics-Controlled Mesh

The physics-controlled mesh is controlled from the node’s window (if the is ). There, in the table in the section, find the physics interface in the column and select or clear the check box in the column on the same table row for enabling (the default) or disabling contributions from the physics interface to the physics-controlled mesh.

Information from the physics will be used to automatically set up an appropriate mesh sequence.


	In the COMSOL Multiphysics Reference Manual see the Physics-Controlled Mesh section for more information about how to define the physics-controlled mesh.

Domain selection

From the list, select any of the options — , , , or (the default). The geometric entity list displays the selected domain entity numbers. Edit the list of selected domain entity numbers using the selection toolbar buttons to the right of the list or by selecting the geometric entities in the window. Entity numbers for voids can be entered by clicking the Paste (

) button in the selection toolbar and supplying the entity numbers in the in the dialog box. The entity number for the infinite void is 0, and finite voids have negative entity numbers.

Selections can also be entered using the window, available from the menu on the toolbar.


	For more information about making selections, see Working with Geometric Entities in the COMSOL Multiphysics Reference Manual.

Physics Symbols

Select the check box to display symmetry planes (in 3D) and lines (in 2D) in the window, as specified in the Symmetry settings.

Symmetry


	For 3D components, from the Symmetry in the yz plane, Symmetry in the xz plane, Symmetry in the xy plane lists, choose Off (the default), Symmetric (infinite magnetic insulation plane), or Antisymmetric (infinite ground plane). Then enter a Plane position (SI unit: m) as required.
	For 2D components, from the Symmetry in the line perpendicular to x and Symmetry in the line perpendicular to y lists, choose Off (the default), Symmetric (infinite magnetic insulation line), or Antisymmetric (infinite ground line). Then enter a Line position (SI unit: m) as required.

Far Field Approximation

To display this section, click the button (

) and select .


	For more information about the Far Field Approximation settings, see Far-Field Approximation Settings in the COMSOL Multiphysics Reference Manual.

Quadrature

To display this section, click the button (

) and select .


	For more information about the Quadrature settings, see Quadrature in the COMSOL Multiphysics Reference Manual.

Thickness (2D components)

For 2D components, enter a default value for the d (SI unit: m). The default value of 1 unit length is typically not representative for a thin domain. Instead it describes a unit thickness that makes the 2D equation identical to the equation used for 3D components.

Infinity Condition


	For 3D components, select the Infinity condition — Magnetic insulation (the default) or Zero magnetic scalar potential at infinity. If there is an antisymmetric symmetry in the potential field, it acts as an added infinite ground plane with a fixed value of the magnetic scalar potential. The value at infinity is fixed to 0 by the presence of the infinite ground plane, so for this case there is only a fixed Zero magnetic scalar potential at infinity condition.
	For 2D components, select the Infinity condition — Magnetic insulation (the default) or Zero magnetic scalar potential at reference distance. If there is an antisymmetric symmetry in the potential field, it acts as an added ground line with a fixed value of the magnetic scalar potential. The value at a reference distance is fixed to 0 by the presence of the ground line, so for this case there is only a fixed Zero magnetic scalar potential at reference distance condition.

Discretization

From the list, choose from predefined options for the boundary element discretization order for the magnetic scalar potential variable and the magnetic flux density variable, respectively. The predefined options represent the suitable combinations of element orders such as (the default).

The settings under are important for sensitivity and optimization computations. See the description of the built-in operators fsens and fsensimag.

Dependent Variables

The dependent variable (field variable) is for the Vm. The name can be changed but the names of fields and dependent variables must be unique within a model.