Modified Hammerstad Model

In Ansys Electronics Desktop, the Hammerstad-Jensen surface roughness model is only implemented for metal layers in SIwave designs and for Finite Conductivity boundaries assigned to applicable edges in 2D Extractor designs. For HFSS and HFSS 3D Layout designs, Hammerstad surface roughness can be mapped to the Huray model when assigning Finite Conductivity boundaries.

This section describes a modified Hammerstad model and how it is expressed as a function of frequency. The Hammerstad model is strictly mathematical. As mentioned above, it is possible to map the Hammerstad surface roughness data to a physics-based Huray model.

The modified Hammerstad model is described by two parameters, the RMS surface roughness and the scale factor SF. In the original Hammerstad-Jensen model, the value of SF = 2.

The model equation is as follows:

Therefore, the model equation reduces to:

The model’s corner frequency fHJ is defined using the formula:

Therefore, the modified Hammerstad model can be written as:

Note:

At low frequencies, the value of HHJ(f) approaches 1. At high frequencies, the value approaches SF.

Additional Reading:

  1. E. Bogatin, D. DeGroot, P.G. Huray, and Y. Shlepnev. "Which one is better? Comparing options to describe frequency dependent losses." DesignCon, 2013.
Related Topics:

Huray Surface Roughness Model

Procedure for Obtaining Broadband Matching between Huray and Hammerstad Models