Add a Background Pressure Field node to add a background pressure wave to model scattering problems solving for the scattered pressure field ps. The total field pt is the sum of the scattered field and the background pressure field pb:

This feature sets up the equations in a so-called scattered field formulation where the dependent variable is the scattered field p = ps. When added, the background pressure field is applied everywhere; it has a locked selection set to all.

In models solved with the boundary element method, it is important that the defined Background Pressure Field is an exact solution to the governing equation. If this is not the case, the results will be unphysical. This means that setting up a user-defined field needs careful consideration.

Select a Background pressure field type: Plane wave (the default), Cylindrical Wave, Spherical Wave, or User defined. Most of the options and settings here are the same as for the Background Pressure Field in The Pressure Acoustics, Frequency Domain Interface.

The only difference lies in the definition of the material properties for the background field. In the BEM interface define a Wave number either picked up from a Pressure Acoustics model in the physics tree (the default), for example, Wave number (pabe/bpam1), or defined From speed of sound. This option ensures that the background field is a solution to the governing equation. If several material models are added, they must have the same speed of sound, to ensure that the background pressure field is a solution to the underlying Helmholtz equation.