Impedance boundary conditions for transient scattering problems

The approximate boundary conditions for the tangential component of the electric field and normal component of the magnetic field on the surface of a homogeneous body of finite conductivity (conductor or lossy dielectric) are derived for transient incident electromagnetic field. Scale factors for basic variables are introduced in such a way, that a small parameter, proportional to the ratio of the penetration depth and body´s characteristic size, appears in the dimensionless Maxwell´s equations for the conducting region and then the perturbation method is used. The use of the boundary conditions together with space-time domain surface integral equations for electric and magnetic fields is proposed. A numerical example is included to illustrate the theory