Here are the addresses of the papers, I had promised, with some dicussions:
1) The Perfect Boundary Approximation Technique Facing the Big Challenge of High Precision Mode Computation
By: P. THOMA, CST GmbH; B. KRIETENSTEIN, T. WEILAND, TU-Darmstadt
Fig.1d indicates that PBA is not perfect perfect. Actually it utilizes the idea of partially filled cells. This clearly means sort of averaging material parameters. Actually the non-orthogonal grid method, in which any cell is completely filled with a single material and conforms to the boundary, deserves the name better.
2) Discrete Electromagnetism with the Finite Integration Technique
By: M. Clemens and T. Weiland
**broken link removed**
On page 7, it mentions 3 schemes for geometry approximation with FIT, which are based on material averaging. One of them is PBA.
3) M. Clemens, T. Weiland: Magnetic Field Simulations Using Conformal FIT Formulations. IEEE Transactions on Magnetics, Vol. 38, N2, pp.389-392, 2002.
This paper describes PBA under another name, i.e. conformal FIT or C-FIT. In the last paragraph of the first column on page 2 it says the C-FIT was first proposed in the paper, which has been mentioned here as number 1. The authors say that C-FIT (PBA) is similar to the work presented in the following paper:
W. Yu, R. Mittra, “A Conformal Finite Difference Time Domain Technique for Modeling Curved Dielectric Surfaces”, in IEEE Microwave and Wireless Components Letters, Vol. 11, No. 1, pp. 25-27 (2001).
For those who have not access to IEEE Xplore, the following paper could be used instead of paper number 3:
Discrete Electromagnetics: Maxwell’s Equations Tailored to Numerical Simulations
By: Markus Clemens and Thomas Weiland
**broken link removed**
You’ll see the same discussion on page 9.
BTW, I'm going to begin a new topic on "hopefully" a future capability of HFSS.
Regards