Local Plane Interface Approximation (LPIA)

The LPIA solver works in the spatial domain (x domain), locally, in a pointwise manner. The solver follows that

• the input field on the surface is treated as a composition of local plane waves (LPWs),
• the part of the surface seen by each LPW is considered a plane interface (locally), and,
• the interaction of the LPW with the local plane interface can be modeled by the Fresnel (or the layer) matrix.

At an arbitrary location on the curved surface, an approximate local boundary condition is applied, which assumes the interaction of the LPW with the local plane interface. Thus, the Fresnel matrix (or layer matrix for coatings) can be used to connect input and output fields.