absorbing boundary comsol

Hi all,

I need to simulate an infinite (in the y direction) dielectric slab with finite width (in the x direction) in COMSOL and see the scattering field, but I do not know how to set the absorbing boundary condition at the edges of the slab.
Does anyone know how to simulate infinite-length geometries in the 2D RF Module of COMSOL?

Thanks in advance,

iaia