HFSS15: Assigning PML Boundaries

A perfectly matched layer (PML) boundary is used to simulate materials that absorb outgoing waves. Setting up a PML boundary is similar to setting up a radiation boundary. You start by drawing a virtual object around the radiating structure. However, instead of placing a radiation boundary on its surfaces, you add PMLs to fully absorb the electromagnetic field.

HFSS can create PMLs automatically, or you can create them manually. Create PMLs automatically if the base object touching the PML is planar and its material is homogenous. HFSS creates a separate PML object for each covered face. The PML boundaries are grouped in the Project tree under the Boundaries icon. Within these groupings, you can edit the radiation parameters (for example, as Incident Wave Port) in order to set up the right total field excitation based on the physical optics approach. PML radiation boundaries are not generated in eigenmode projects.

In creating PMLs, you can select non rectangular sheet objects as long as they do not touch any other selected face. The underlying object does not have to be a box. If there are faces that touch, the touching faces must be locally box-like. You can assign variables to the dimension properties of the base object. Changing the variable values also changes the associated PMLs.

PML Compared to Radiation Boundaries

Compared to Radiation boundaries, which create absorbing boundary conditions (ABC), PMLs in general make it more difficult for the iterative solver to reach convergence compared to the same model with using ABCs. PMLs also require significantly more RAM. The advantages for PMLs are that they absorb a much wider range of waves in terms of frequency and direction. As a result, you can put PMLs much closer to the discontinuities. This gives a smaller model. ABCs efficiently absorb normal incident waves. You have to put ABCs far away enough from the discontinuities.

What do you want to do?

Create PMLs automatically.

Create PMLs manually.

Guidelines for Assigning PML Boundaries