To calculate the scattering, absorption, and extinction cross sections of a scatterer, add a Cross Section Calculation node. The scattering cross section is calculated as

Here, n is the normal vector pointing outward from the scatter, Ssca is the scattered Poynting vector, and I0 is the intensity of the incident plane wave. The integral is performed over the surface enclosing the scatterer.

The intensity of the incident wave can be calculated from the electric field amplitude E0 as

Here, k and k0 are the wavenumber in the background medium and free space, respectively, c is the free space speed of light and ε0 is the free space permittivity.

Here, Q is the power loss density in the scatterer and the integral is performed over the volume V of it.

The Cross Section Calculation node is only available when Scattered field is selected from the Formulation list in the Settings window of the physics interface, and the Background wave type is set to

Enter the Incident plane wave intensity when the Background wave type is set to User defined for 2D and 3D. The default value is 1 W/m2.