When the Background Acoustic Fields feature is added to a domain, it is possible to define the value of the background acoustic field variables pb, ub, and Tb. Use this feature to set up scattering problems. To define fields at the inlet of a waveguide it is recommended to use the Port condition.

This section contains field variables that appear as model inputs. The fields are always active as the equilibrium (background) temperature T0 enters the governing energy equation explicitly. It is used for the Plane wave option.

Select the Acoustic field type — User defined (the default) or Plane wave.

When User defined is selected, enter expressions for the Background acoustic pressure pb, the Background acoustic velocity ub, and the Background temperature variation Tb. These can be analytical expressions or values of dependent variables solved in a previous study that defines the background field.

When Plane wave is selected, enter the Pressure Amplitude |pb| (given at x = 0) and the wave direction vector ek (this vector is automatically normalized). Finally, select where the Material data should be taken from; the default is From material model (the same as the domain model material) or select a material from the list. This will set up the background pressure, velocity, and temperature variations for a plane wave with the correct thermoviscous attenuation compatible with the governing equations.