# Method of Moments

When the solver method has been set to MoM, there are extra settings that can be selected in order to configure how the analysis is made during the simulation process.

It is possible to set the electromagnetic equation as well. This option is only available when the solver method has been set to MOM. This electromagnetic equation defines the integral equation to solve during the simulation process. There are three possible equations:

• EFIE makes use of the Electric Field Integral Equation, which solves most of the problems provided a that a good convergence is achieved.
• MFIE makes use of the Magnetic Field Integral Equation. Note that this solver requires geometries to be closed, having their normal vectors pointing outside the objects, in order to obtain valid results.
• CFIE combines EFIE with MFIE -therefore, requirements for MFIE also apply on CFIE. CFIE uses a weighted combination of EFIE and MFIE. The CFIE Parameter sets this weight. CFIE uses the following equation:

CFIE = EFIE · α + MFIE · (1 - α)

Tip EFIE is best recommended on projects with open surfaces, although it works on closed surfaces as well. CFIE is best suited for closed metallic surfaces. You can use a combined approach using EFIE for some surfaces and CFIE for closed surfaces.

Warning if the solver uses the CFIE approach, it is mandatory for the normal vectors to be facing outside. Unexpected results and likely errors will happen if normal vectors point inside of volumes.

The selected solver function is ued to set the electromagnetic technique being used through the simulation process:

• If the subdomains option is chosen, the MLFMA-MoM (Multi-Level Fast Multipole Algorithm) will be used. This is the most conventional technique.
• If the macro basis functions (CBFs) option is selected, then the CBFM-MLFMA (Characteristic Basis Function Method - Multi-Level Fast Multipole Algorithm) is used instead. This option improoves the convergence of the MLFMA algorithm, reducing CPU consumption and time since the number of unknowns is reduced.

Tip: CBFs approach is more efficient than the subdomains approach. However, the CBF method has accuracy issues in cavities.