== Defining the Physical Structure in EM.Ferma ==
The simplest static problems involve a charge source in the free space that produces an electric field, or a current source in the free space that produces a magnetic field. In such cases, the only applicable boundary conditions are defined at the computational domain boundary. As soon as you introduce a dielectric object next to a charge source or a magnetic (permeable) material next to a current source, you have to deal with a complex boundary value problem. In other words, you need to solve the electric or magnetic Poisson's equation subject to the domain boundary conditions as well as material interface boundary conditions. EM.Ferma used the Finite Difference technique for numerical solution of your static boundary value problem.
For static analysis, the model can be excited with any number of Voltage Sources, Charge Sources, or Current Sources. For Quasistatic analysis, only Voltage Sources are of practical use.
=== Voltage Sources Fixed-Potential PEC Objects=== A perfect electric conductor (PEC) is a material with ε<sub>r</sub> = 1 and σ = ∞.
In EM.Ferma, Voltage Sources are applied to a specified PEC material group that exists in [[EM.Cube|EM.CUBE]]'s navigation tree. All CAD objects under the specified PEC group will act as Voltage Sources.