# CO Card

This card specifies a dielectric or magnetic coating of wire segments or triangular surface elements.

In the Home tab, in the Define group, click the   Media icon. From the drop-down list select the  Coating (CO) icon.

Note: The coating applies to all calculations following the CO card.

The CO card uses the material properties (label of the material) defined in the DI card. Therefore the DI card must be placed before the CO card. A layered medium is defined by referencing the labels of the materials to be used for the individual layers in the DL card.

## Parameters:

Label of elements to coat
All segments or triangles with this label are coated.
No coating (as if CO card not present)
No coating present (as if the relevant label has no CO card). This is used to remove wire coatings from earlier solutions.
Wire coating (Popovic formulation)
In this case, the radius of the metallic core is changed internally to model the change in the capacitive loading of the wire and a corresponding inductive loading is added. The only restriction of this method is that the loss tangents of the wire coating and of the surrounding medium must be identical (for instance both media could be lossless).
Wire coating (volume equivalence principle)
This setting retains the radius of the metallic wire. The effect of the dielectric layer is accounted for by a volume polarisation current. The only restriction of this method is that the layer should not be magnetic in nature. This means that the relative permeability ${\mu }_{r}$ as well as the magnetic loss tangent $\mathrm{tan}{\delta }_{u}$ of the coating must be the same as those of the surrounding medium).
Electrically thin surface coating
This option adds multilayer dielectric/magnetic coatings to the surface triangles with the specified label. Different values for the permittivity and permeability of the layers are allowed, but the total coating must be electrically (that is relative to the wavelength in the coating) thin as well as geometrically thin (see the next item).
Dielectric / magnetic surface coating

This option adds electrically thick multilayer dielectric/magnetic coatings to the surface triangles with the specified label. This option requires that the total coating should be geometrically thin (relative to the triangle size, and as a result of the triangle size, also to the free space wavelength) as well as the curvature radius of the surface.

This option may also be used when using the MoM / MLFMM and a single-layered, electrically thick, but geometrically thin coating is applied.
• Only for closed structures with a PEC surface and the normal vector pointing towards the source(s).
• Coating is applied to both sides of the PEC surface, since fields will be zero where there is no sources.
• The accuracy of this option is higher when the propagation constant is high (high losses / permeability / permittivity).
Material label
Label of the material (as specified in the DI card) that will be used as a coating.
Layered dielectric label
Label of the layered dielectric medium (as specified in the DL card) that will be used as a coating.
Thickness of coating
For surface coatings, the thickness hn of each respective layer. For wire coatings this is the radius of the coating less the radius $\varrho$ of the wire-core. This value is in metres and is scaled by the SF card.
Wire radius $\varrho$ of the metallic wire, without layers, in metres (it is scaled by the SF card). This overrides the values specified in the IP card. This field is only applicable to wire coatings.
• The loss tangent $\mathrm{tan}\delta$ of the layer (which is calculated from the conductivity $\sigma$ and the relation $\mathrm{tan}\delta =\frac{\sigma }{\omega {\epsilon }_{r}{\epsilon }_{0}}$ ) has to be identical to the loss tangent of the surrounding medium.
• For pure dielectric layers (that is the relative permeability ${\mu }_{r}$ as well as the magnetic loss tangent $\mathrm{tan}{\delta }_{u}$ of the layer are equal to those of the surrounding medium) the option Wire coating (Volume equivalence principle) is recommended.