# User Defined Surface Impedance

This option allows the definition of a complex user defined surface impedance,
Z_{s}.

## Parameters:

- Material label
- Label of the material which will be used as the defined surface impedance (as specified in the DI card).

For example, to model a solid dielectric object with relative permittivity ${\epsilon}_{r}$ and with conductivity $\sigma $ at a specific angular frequency $\omega =2\pi f$ the following surface impedance expression can be used:

The user defined complex surface impedance Z_{s} relates to the surface current
**J**_{s} and the E-field by
${E}_{tan}={Z}_{s}{J}_{s}$
where
${E}_{tan}$
is the tangential E-field and
${J}_{s}$
is the surface current density.