CST2013: Tabulated Surface Impedance

Modeling: MaterialsNew/EditNew MaterialType: Surface imp. (table) Properties
Edit Object Properties (navigation tree: Materials:material1PropertiesType: Surface imp. (table) Properties)

This dialog allows to define a frequency dependent, isotropic surface impedance model. The data is provided in tabulated form, with the resistance and reactance given for discrete frequencies. This option is available for the transient solver and the frequency domain solver with tetrahedral mesh. See the material overview for details.

Surface impedance

Fitting scheme: For the Tabulated Surface impedance the only available dispersion model is General Nth order, due to its wide range of application and generality. For detailed information about this scheme see the Material Overview.

Frequency/Resistance/Reactance/Weight:

In this list box, the specific resistance and reactance can be defined by setting several values at different frequency points. Moreover to each frequency a weight (value greater than/equal to 0.0) is assigned in order to direct the interpolation algorithm and to enforce a reduced error in correspondence of the given frequency point.

An important observation is that in correspondence of General Nth order fitting, due to specific algorithm requirements, the weight behaves as a switch between considered and ignored samples. A weight less then 1.0 forces the interpolation algorithm to ignore the given sample, whereas a weight greater/equal 1.0 to consider the sample itself.

Max order: This control, available in case of General Nth order fitting, enables the user to specify the maximum allowed model order (total number of real and complex poles each counted with the corresponding multiplicity). The search of the best fitting model is then stopped to the given maximum order even if the error convergence criterion is not fulfilled.

It should always taken into account that increasing the model order may improve the quality of the fitting but at the same time the simulation complexity in terms of memory and computational time.

Used order: Displays the effective model order provided by the interpolation algorithm. The model order corresponds to the total number of real and complex poles each counted with the corresponding multiplicity (in formulas, Order = num Real Pole + 2 x num Complex Poles).

Error limit: This control, available in case of General Nth order fitting, enables the user to specify the error stopping criterion during the search of the best fitting model. The error should be interpreted as the maximum relative error computed in correspondence of each given frequency point between the (complex) impedance value and the fitting curve. A useful interpretation of the Error limit is as "error" or "inaccuracy" during measurement of the real material properties.

Error: Displays the obtained fitting error. The error should be interpreted as the maximum relative error computed in correspondence of each given frequency point between the (complex) impedance value and the fitting curve.

Details...: Opens a dialog displaying information about the fitted model, in terms of position of zeroes and poles in the complex plane for the impedance transfer function, see also Material Overview (HF).

The representation is subdivided in constant, linear, first and second order contributions.

The constant term corresponds to a frequency independent contribution, whereas the linear term is related physically to the contribution of an inductance (purely reactive element).

The first order contribution corresponds to a real pole, whose frequency is computed and shown.

The second order contribution may derive from a couple of real poles or from a couple of complex conjugate poles. In the former case the frequency of the poles is computed. In the latter case the resonance frequency of the pole together with the quality factor (Q) is shown.

The description of these parameters and the mathematical formulas that relate the first and second order polynomial coefficients to the physical interpretation of poles, zeroes and resonance frequencies may be found in Material Overview (HF).

Use data in frequency range: This control, available in case of General Nth order fitting, allows the fitting algorithm to use only the frequency data points that lie within the "frequency range settings" defined by the user (see also Frequency Range Settings). Activating this check box enables an accurate data fitting of the material resonances which occur in the simulation bandwidth of interest using possibly a reduced number of poles and zeroes with respect to the complete data fitting. And this, in turn, translates into benefits for the simulation complexity in terms of memory and computational time.

Transparent sheets: Sheets may be either transparent, with the electric field being the same on both sides of the sheet, or opaque, which means that there will not be any direct coupling between front- and back-side of a sheet.

Load File...: Opens a file selector dialog to specify a ASCII file containing point coordinates.

The file is formatted in lines which specify the frequency points. Each line has four entries specifying respectively frequency, value of real and imaginary part of the impedance (i.e. resistance and reactance) and weight. The weight field may be skipped and is assumed by default equal to 1.0.

Moreover it is possible to set a default frequency unit scale which is applied to all loaded data samples.

Delete: Press this button to delete all selected rows in the impedance versus frequency list box.

Clear List: Press this button to delete all entries of the impedance versus frequency list box.

OK

Accepts the input and closes the dialog.

Cancel

Closes this dialog box without performing any further action.

Apply

To apply the settings and show the fitted curve.

Help

Shows this help text.