HFSS15: Design Settings for HFSS

The HFSS>Design Settings command displays a dialog with tabs for Set Material Override, for automatic Lossy Dielectrics and for DC Extrapolation. For Transient designs, the dialog contains a Transient tab.

Set Material Override Tab

The Set Material Override tab includes text note and a checkbox to Allow metals to override dielectrics. The purpose of this feature is to allow you to avoid doing explicit subtraction in the modeler. One example application is a via that passes through many dielectric layers--with the option turned on, the via does not have to be subtracted from the layers.

The Set Material Override option allows some intersections to be resolved automatically in the mesh. If metal intersects dialectric, the metal overrides the dialectric in the overlap region. (That is, the metal object is subtracted from the dialectric.) If objects with the same material overlap, the small object overrides the larger. (That is, the small object is subtracted from the larger.) All other intersections are treated as errors. Normally, the modeler considers any intersection between 3D objects to be an error.

To use this feature, check Enable material override.

In the meshing process, the dielectrics are locally overwritten by the metals in the intersecting region. That is, the part of the dielectric that is inside the metal is removed, and if the dielectric is completely inside, the whole object disappears.

Lossy Dielectrics Tab

By default, HFSS automatically applies frequency dependent lossy materials for the solver and post processor. The materials are not modified in the design. Instead, the Djordjevic-Sarkar model is applied before the material is passed to the solver or used for post processing. You can disable this feature on the Lossy Dielectrics tab.

This feature addresses cases where you only have simple constant material properties available, but want to automatically apply a general-purpose frequency dependence to ensure causal solutions when solving frequency sweeps.

When enabled the Djordjevic-Sarkar model is applied to all constant lossy dielectrics . These are defined as having a constant permittivity that is greater than one and a constant loss tangent that is greater than zero. The inputs to the Djordjevic-Sarkar model are the material's constant permittivity and loss tangent, plus the standard default values of measurement frequency (1 GHz), DC conductivity (1e-12 S/m), and DC permittivity (none ). The outputs from the Djordjevic-Sarkar model are the expressions for permittivity and conductivity. These expressions, plus zero loss tangent, are used in place of the material's constant properties.

When reading legacy designs (HFSS 12 and earlier), this feature is unchecked.

DC Extrapolation Tab

The DC Extrapolation tab option affects Interpolation Sweep setup. If you select Standard DC Extrapolation, the software computes values automatically, and the tab for DC Extrapolation does not appear on the Interpolating Sweep setup.

For Advanced DC Extrapolation, the Interpolating Sweep setup includes the DC Extrapolation tab, so you can set a Minimum solved frequency.

The Design Settings dialog also contains checkboxes to Save As Default.