Figure 12: Region properties dialog. The program remains in line entry mode. Draw another vector along the y axis from [0.0, 0.0] to [0.0, 15.0]. Right click the mouse to exit line entry mode. To add the circular edge of the region, choose the Arc/Start-end-center tool. Move the mouse to the following locations in sequence and click the left button at each one: [15.0, 0.0], [0.0, 15.0], [0.0, 0.0]. You should see the arc vector of Fig. 11 . With the outline of Region 1 complete, we shall set the region properties. Choose the command Settings/Region properties to bring up the dialog of Fig. 12 . Region 0 is a special place to store reference vectors that will not appear in the output script.
Supply the name Dielectric for Region 1 and check the Filled box. For a filled region, Mesh assigns not only the nodes of the boundary to Region 1 , but also the elements enclosed. The Filled property applies to regions with non-zero volume. Exit the dialog. Next, we are going to create the inner electrode by over-writing a portion of the dielectric volume. Click the Start next region tool, Now, all vectors you enter will be associated with Region 2 . This region has the same shape as Region 1 except that the radius is 5.0 rather than 15.0. Use the same procedure except the first line should extend from [0.0, 0.0] to [5.0, 0.0] and so forth. When complete, go to Settings/Region properties .
Assign the name InnerElectrode to Region 2 and set the Filled property. Exit the dialog. To check the work so far, click the Toggle fill display tool to bring up the plot of Figure 13 . The fill display mode is both a diagnostic and a visual aid. It checks that the vectors of filled regions define a closed surface and shows how the enclosed elements have been assigned. Click the tool again to return to the normal vector display. We’ll conclude by defining Region 3 . This region is not a filled volume but rather a set of nodes set to the fixed-potential condition on the outer boundary. We call such a region an un-filled or line region.
Click the Start next region tool and then the Arc/Start-End-Center tool. Move to the following coordinates in sequence and click the left mouse button: [15.0, 0.0], [0.0, 15.0], [0.0, 0.0]. The nodes on the outer edge of Region 1 are re-assigned to Region 3 (color-coded violet). Set the region name to OuterBoundary and be sure that the Filled box in unchecked. You may ask whether it’s necessary to set special conditions on the dielectric 17