3.5     Asymptotic Boundary Conditions (wire grids)

Asymptotic boundary conditions (ASBC) have been introduced following a suggestion of some of QuickWave users. ASBC are defined by setting to zero one of the electric field components over the region covered by ASBC, and thus can be realised as wire grids. Regarding the orientation and geometry of ASBC, the following restrictions apply in QW‑3D:

·        ASBC can only be defined in planes perpendicular to one of the coordinate axes;

·        in vertical planes (parallel to XZ, YZ) ASBC must have a rectangular shape;

·        in horizontal planes (parallel to XY) arbitrarily-shaped ASBC can be drawn, but a stair-case approximation will be made.

Table below specifies the correspondence between the ASBC orientation (horizontal (H)/vertical (V)) and the electric field component effectively set to zero

Note that formally speaking, ASBC can also be introduced by drawing appropriate grids of individual wires. There is, however, one major practical difficulty in such an approach: the user has to draw each wire separately, exactly following the existing FDTD mesh. After re-meshing of the project, the wire grid has to be re-drawn. Those problems are avoided by application of special elements, which we call "wire grids". Drawing a wire grid really means drawing a frame (rectangular in XZ, YZ planes; arbitrarily-shaped in XY plane), which is then filled with wires of a horizontal (H) or vertical (V) orientation. The number and locations of wires in the grid automatically adjusts to the mesh and mesh changes.

More details regarding drawing and using the ASBC in simulation scenario can be found in Wire Grids.