# Plane wave coupling¶

Warning

The plane-wave coupling module is still in development, and its current functionality is experimental.

If non-spherical particles are located such that their circumscribing spheres overlap, the conventional superposition T-matrix method is not applicable. A coupling method based on a temporary plane wave expansion of the scattered field was developed [Theobald 2017] in order to allow for simulations also in such cases.

Right now, the plane wave coupling can be used if

• direct matrix inversion is selected, see Solver settings.
• m_max is set to l_max for all particles.

## Use PVWF coupling in a Smuthi simulation¶

To activate the PVWF coupling feature in a Smuthi simulation, set the use_pvwf_coupling parameter of the simulation constructor to True and provide a suitable $$n_{eff}$$ truncation and discretization with the pvwf_coupling_neff_max parameter and the pvwf_coupling_neff_resolution parameter of the simulation constructor:

simul = smuthi.simulation.Simulation( ...,
use_pvwf_coupling=True,
pvwf_coupling_neff_max=7,
pvwf_coupling_neff_resolution=1e-2)