A shielded electrical microstrip transmission line is fixed to a substrate and placed in a shielded container of air. The simulation applies a known voltage to the strip to calculate the resulting capacitance and compares this with the theoretical result. The problem assumes symmetry in the lengthwise direction so that the model can be reduced to a 2D planar cross-section. The strip is represented by an internal boundary to which the voltage is applied.
This model is available as an automated tutorial by selecting Model Examples and Tutorials… > Electromagnetics > Microstrip Transmission Line from the File menu. Or alternatively, follow the linked step-by-step instructions.