Boundary Type

H-Field Behavior

Used to model...

Default Boundary Conditions (Natural and Neumann)

Field behaves as follows:

• Natural boundaries — H is continuous across the boundary.
• Neumann boundaries — H is tangential to the boundary and flux cannot cross it.

Ordinary field behavior. Initially, object interfaces are natural boundaries; outer boundaries, and excluded objects are Neumann boundaries.

Zero Tangential
H Field

The tangential components of H are set to zero. Flux is perpendicular.

External magnetic fields.

Integrated Zero Tangential H Field

For applications such as a motor with the shaft excluded, there remains a hole in the middle. In such cases, on the hole's boundary, neither the Tangential H Field boundary (where integration of the tangential H field is non-zero), nor the Zero Tangential H Field boundary (where the tangential H field is zero everywhere) can be applied because – for the hole boundary case – integration of the tangential H field is zero, but the tangential H field is not zero everywhere. Integrated Zero Tangential H Field can be used for such applications.

Cases such as the boundary around the hole that remains when a motor's shaft is excluded.

Insulating

Same as Natural boundary, except that current cannot cross the boundary.

Thin, perfectly insulating sheets between touching conductors.

Symmetry

Field behaves as follows:

• Odd Symmetry (Flux Tangential) — H is tangential to the boundary; its normal components are zero.
• Even Symmetry (Flux Normal) — H is normal to the boundary; its tangential components are zero.

Planes of geometric and magnetic symmetry.

Matching
(Independent and Dependent)

The H-field on the dependent boundary is forced to match the magnitude and direction (or the negative of the direction) of the H-field on the independent boundary.

Planes of symmetry in periodic structures where H is oblique to the boundary.

Resistive Sheet

Same as Natural boundary.

Voltage drop and loss on the contact surface between two different objects within a conduction path.

Impedance

Includes the effect of induced currents beyond the boundary surface.

Conductors with very small skin depths.

Touching

Interface between a moving part and a stationary part.

Thin Layer (Air Gap)

When two parts of the domain are separated by a thin volume representing an air gap, it can be modeled by a surface with an appropriate boundary condition. This boundary creates a field discontinuity between the two sides of the selected surface based on its thickness. The relative magnetic permeability of the air gap is assumed to be equal to one.

Narrow air gaps