7.6.1   Suppress singularity corrections

It is commonly known that near metal corners, edges and thin wires strong field singularities appear. To enhance the modelling accuracy, in QuickWave special mathematical models of field singularities have been implemented. Those models are in brief called singularity corrections. For wires, such singularity correction are made automatically (singularity correction will be applied to H-field encircling the wire, and E-fields perpendicular to the wire). To enable singularity corrections along metal blocks or thin metal layers, the user should ensure that respective edges coincide with the edges of FDTD cells (e.g. by setting mesh snapping planes).

The models of field singularities decisively increase the accuracy of the analysis of e.g. planar structures, especially in terms of characteristic impedance of the strips. When applied, they produce good approximation of the characteristic impedance of the strip even with 2-3 FDTD cells across the strip width. Without them similar accuracy can be obtained with 7-8 FDTD cells per strip width. That is why it is recommended that the mesh snapping planes of electric type be placed along the strip edges. A practical example is discussed in User Guide 3D: Planar circuit example.

In QuickWave, the singularity corrections algorithms are by default active, however, the user is provided with a feature that allows suppressing the models of field singularities in the calculations. This feature is called Suppress singularity corrections. Suppress singularity corrections means that field singularity corrections will not be applied at metal edges, corners and wires. This option is typically provided for specific software operation and software development purposes. It allows inspecting how pronounced field singularities are in a particular scenario and evaluating the influence of field singularities on the accuracy of FDTD results.

The effect of field singularity corrections can be watched based on User Guide 3D: A simple waveguide example.