The Background Field feature triggers the scattered field formulation, where the dependent variable is the relative field. The same wave equations are used as in the full field formulation, but the total field that enters the equations are written as the sum of the relative field and the background field, E = Erelative + Ebackground, and it is the dependent variable Erelative that is solved for. When the background field is a solution of the wave equation, the relative field is the scattered field.

Select a Background wave type — User defined (the default), or Modulated Gaussian pulse.

Enter the component expressions for the Background electric field Eb (SI unit: V/m) and Background magnetic field Hb (SI unit: A/m). The entered expressions must be differentiable in time domain since the derivative of the background field is used in the governing equations.

Select a Direction of propagation — +x (the default), -x, +y, -y, or for 3D components, Along the +z, or -z.

Select a Polarization direction— y (the default), z, or x. The list of available polarization varies based on the selection of Direction of propagation.

For a modulated Gaussian pulse propagating in the positive x direction, the electric field is expressed as

where τ is the pulse duration, defined as 1/2f0, μ is a time delay set to 2/f0, and vp is the phase velocity. The time delay μ is used to excite a modulated Gaussian pulse whose initial magnitude is very small when it is launched and gradually increases as it propagates.