user's guide – High Frequency Structure Simulator

Boundary Conditions
1.1
Technical Definition of Boundary Conditions
Excitation – An excitation port is a type of boundary condition that permits energy
to flow into and out of a structure. See the section on Excitations.
Perfect E – Perfect E is a perfect electrical conductor, also referred to as a perfect
conductor. This type of boundary forces the electric field (E-Field) perpendicular
to the surface. There are also two automatic Perfect E assignments:
Any object surface that touches the background is automatically defined to
be a Perfect E boundary and given the boundary condition name outer.
Any object that is assigned the material pec (Perfect Electric Conductor) is
automatically assigned the boundary condition Perfect E to its surface and
given the boundary condition name smetal.
Perfect H – Perfect H is a perfect magnetic conductor. Forces E-Field tangential
to the surface.
Natural – for a Perfect H boundary that overlaps with a perfect E boundary,
this reverts the selected area to its original material, erasing the Perfect E
boundary condition. It does not affect any material assignments. It can be
used, for example, to model a cut-out in a ground plane for a coax feed.
Finite Conductivity –A Finite Conductivity boundary enables you to define the
surface of an object as a lossy (imperfect) conductor. It is an imperfect E
boundary condition, and is analogous to the lossy metal material definition. To
model a lossy surface, you provide loss in Siemens/meter and permeability
parameters. Loss is calculated as a function of frequency. It is only valid for
good conductors. Forces the tangential E-Field equal to Z s (n x H tan ). The
surface impedance (Z s ) is equal to, (1+j)/(δσ), where:
δ is the skin depth, (2/(ωσµ)) 0.5 of the conductor being modeled
ω is the frequency of the excitation wave.
σ is the conductivity of the conductor
µ is the permeability of the conductor
Ansoft High Frequency Structure Simulator v 9.0 User’s Guide
1.1-4